Perttu Pulkkinen
2005-09-14 23:14:11 UTC
Joku dekkaristin alku, tässä pikaisen novellin aihe, jos juttu ei selviäkään
lähiaikoina:
Luettuna ao. helik.onnettomuusselvitys tuntuu kiehtovasti mystiseltä, koska
siinä täysin "sivuutetaan" ennen nollahetkeä ollut 37-sekunnin 'emergency
situation', vaikka myöhemmin mainitaan ettei siinä (muka?) ollut mitään joka
auttaisi syyn selvittämisessä.
Selvästi kirjailijan mielikuvitus alkaa lentää: mitä oikein tapahtui,
murhattiinko joku, tekikö joku itsarin, ...
Kirjoittais ny joku vaikka tänne novellin "37 SEKUNTIA"...
tv Perttu Pulkkinen, jkl
Ps. toki todellisuudessa varmaan syy raporin salamyhkäisyyteen on siinä,
että siinä vain poissuljetaan muita syitä eikä ehdotella mitään, mutta eikö
tällaisista aineksista hyvät dekkarit hiukan liioittelemalla saa
käyttövoimansa normaalistikin?
***********************************************************************
PRELIMINARY REPORT
AIRCRAFT ACCIDENT INVESTIGATION COMMISSION
Aircraft Accident involving helicopter Sikorsky S76 C+
Registration mark OH - HCI
Tallinn Bay, 10 August 2005
TALLINN
2005
SYNOPSIS
On 10 August 2005 at 12:45 local time, an accident occurred with helicopter
Sikorsky S76C+, registration OH - HCI, on its scheduled passenger service
from Tallinn to Helsinki. All the 14 occupants of the helicopter were killed
in the accident, the helicopter was destroyed. The helicopter hit the water
2 km southwest of the island of Aegna. i.e. at the 12 km distance of the
take-off place at the City Hall heliport and sank to the depth of 45 meters.
None of the occupants of the helicopter were found in the course of search
and rescue operation that started immediately. Only a light trace of oil
pollution and the helicopter main rotor blade floating on the surface of the
sea were found close to the accident site.
The wreckage of the helicopter was found 5 hours later with the help of
robot. The operation of rescuing the bodies of the victims of the accident
started the next day. Divers succeeded in lifting the bodies of all the 13
victims who had occupied the helicopter in 24 hours. The body of one of the
victims (pilot-in-command of the helicopter) was found 15 days later in the
course of additional search operation approximately 45 off the place were
the helicopter sank.
The wreckage of the helicopter was lifted to the surface on the third day
after the accident (13.08.2005.a.) and was it taken to the hangar on Tallinn
airport for the purpose of examination
On the day of the accident, a 8-member commission for investigating into the
causes of the accident was appointed under the decree of the Minister of
Economic Affairs and Communications. The composition of the commission is as
follows:
Chairman:
Taivo Kivistik Deputy Secretary General, Ministry of Economic Affairs and
Communications
Deputy Chairman:
Tõnu Ader Executive Officer, Emergency Management Department, Ministry of
Economic Affairs and Communications
Members of the Commission:
Oleg Harlamov Counsellor to the Minister, Ministry of Economic Affairs and
Communications
Mati Iila Counsellor, Emergency Management Department, Ministry of Economic
Affairs and Communications
Tiit Kaurla- Executive Officer, European Union and International Cooperation
Department, Ministry of Economic Affairs and Communications
Toomas Kasemaa Head of the Bureau of Border Guard Policy, Internal Security
Policy Department, Ministry of the Interior
Aleksander Dintsenko Senior Inspector, Department of Air Traffic Services
and Aerodromes, Civil Aviation Administration
Jaanus Ojamets Senior Inspector, Flight Operations Department, Civil
Aviation Administration
USA as a State of Manufacture and the State of Design of the helicopter
appointed Aircraft Accident Investigator Ms Lorenda E Wardi, National
Transportation Safety Board (NTSB), as its official representative at the
Commission.
Finland as the State of Operator appointed Aircraft Accident Investigator at
the FinlandŽs Aircraft Accident Investigation Centre, Mr Hannu Melaranta as
its official representative at the Commission.
Preliminary report of the aircraft accident investigation was signed on 12
September 2005.
BODY
1. FACTUAL INFORMATION
History of the flight
Helicopter Sikorsky S76C+ with registration mark OH - HCI, with 12
passengers and 2 pilots as crew members on board, departed from Tallinn City
Hall heliport on 10 August 2005 at 12:39 p.m. local time (i.e. at 09:39 UTC)
and started its normal flight on the route to Helsinki. The flight on the
route usually lasts 18 minutes, the distance is 80 km.
The crew of the helicopter, consisting of Finnish nationals, had performed 5
landings on Tallinn City Hall heliport that day. Weather was suitable for
the flight and another take-off (i.e. the fifth one) at the direction of
Helsinki took place as usual, not to mention the delay from schedule due to
the delays of previous flights. 6 nationals of Finland, 4 nationals of
Estonia and 2 nationals of USA, including 7 women and 5 men, were on board
of the helicopter as passengers. Before take-off, automatic passenger
briefing was started in Finnish, Estonian and English languages. There were
no problems with completing pre-flight and after-take-off checklists.
Pilot-in-command sitting on the right seat was the pilot flying. After the
take-off on heading 110°, the helicopter turned left and continued the
flight on heading 355° with acceleration and climb. Air Traffic Controller
of the Tallinn Tower was reported that the helicopter was airborne.
After reaching the altitude of 1500 ft (according to the flight recorder
2000 ft standard atmosphere) and the speed of 130 knots and approaching the
border of Tallinn Airport Control Zone, the crew assessed the cloud
conditions ahead and prepared to climb to the altitude of 2000 ft or higher.
After telling the co-pilot that he was going to add some power, the
pilot-in-command started to raise the collective. Energetic raising of the
collective took place 5 seconds after that moment. Until that moment, the
flight had proceeded as normal, but starting from that moment (hereinafter
"moment 0"), an emergency situation occurred, which lasted for 37 seconds
and ended with helicopter` s striking the water. According to the flight
recorder recording, the raising of the collective was followed by active
pulling of the cyclic approximately half of the maximum travel and immediate
(a second later) fully forward movement of the cyclic for a very short
period . The pulling of the cyclic was followed, according to the cockpit
voice recorder recordings, by the exclamation by the pilot-in-command and, a
warning signal. At the same time, according to the flight recorder
recordings, the increase of vertical acceleration in 1.5 seconds from + 1G
to +3 G took place.
When 1.5 seconds had passed from the moment 0, the helicopter was in the
following attitude:
pitch had increased to 40° and continued to increase;
roll to the left was 40° and continued to increase;
heading had changed from 355° to 320°, i.e. the front part of the helicopter
had turned left by 35° comparing to the initial heading and the turn to the
left continued for more 4 seconds.
The helicopter lost speed, but at the same time climbed for approximately
200 ft (up to the altitude 1700 ft) and maintained this altitude in about 10
seconds, after which the altitude started to diminish with unstable rate of
descent. During the next half a minute, the helicopter changed its attitude
irregularly, to which the crew reacted by acting with helicopter controls.
After the occurrence of emergency situation the cockpit voice recorder had
not recorded any comments by the crew that could explain the causes of the
occurrence and the helicopter`s unusual attitude. The only clearly
distinguishable phrases were three fast and weakly audible "May Day" calls
by the pilot-in-command and a question by the co-pilot "The tail has gone?"
Air Traffic Controller in Tallinn Tower, who was about to communicate to the
helicopter their take-off time and the information to contact the air
traffic controller of Tallinn approach area on the frequency 127,9 MHz,
noticed the abrupt change of helicopter`s heading and the following loss of
altitude as well as the disappearance of the radar indication from the
screen.
The last seconds of the accident were witnessed by a captain of a pilot boat
in port approximately 3 km away from the accident site. The helicopter
attracted captain`s attention because of some consecutive loud banging
sounds. He called immediately to the emergency service and contacted a pilot
boat that was close to the accident site. The boat arrived at the accident
site about ten minutes after the accident.
At the same time (at 12:55 pm) the search and rescue helicopter of the
Border Guard Aviation Group took off from Tallinn airport and arrived at the
accident site approximately 20 minutes after the accident.
According to the recordings of flight recorder, the helicopter turned first
left up to the heading 250° (at the moment 4 s) after which the helicopter`s
heading started to increase again (the helicopter turned right). Spinning of
the helicopter to the right continued till it hit the water. In
approximately half a minute, the helicopter made 13 full turns and hit the
water on heading 360º.
The collective of the helicopter was in the position of active climb during
the period from the moment 0 to 3 seconds. Until the moment 9 s, it
maintained the position close to that of maximum climb. After that the
collective abruptly resumed the position it had before the moment 0. Later,
the collective continued to move downward and was close to lowest position
at the last seconds of the flight.
Helicopter rotor revolutions were between 100% and 110% most of the time,
except for the period from 4 to 12 seconds, when the rotor speed was
significantly lower than normal and fell for a moment (at the moment 6 s) to
70%.
Both engines of the helicopter were running and producing the power
necessary for rotors` rotation.
The helicopter continued to spin irregularly and finally hit the water and
turned immediately over.
Emergency floatation system did not activate.
The helicopter was quickly filled with water and sank into the sea in
approximately 10 seconds.
1.2. Injuries to persons
All the occupants of the helicopter were killed.
Damage to aircraft
The aircraft had sunk 45 m into the water. One the main rotor blade had
injured tail boom and cut through the mechanic transmission of the tail
rotor, but the tail cone of the helicopter had retained its integrity. As
the result of the impact of the blade, the transmission shaft and its cover
had removed to the extent of about 1 meter. The parts that had torn off were
lying at about ten metres` distance from the helicopter wreckage on the
seabed and they were rescued by divers.
Main rotor hub was in its normal position and root parts of all the four
main rotor blades had similar damages, only the length of the parts of the
blades attached to the hub was varying. Blades vibration absorbers (dampers)
had also broken off.
Panels of the stabilizer had damages indicative of the impact of hitting the
water, the right panel had separated from the tail. The left part of the
tail gearbox together with tail rotor had broken off its main part and were
lying apart from the helicopter. However, there were no detectable damages
to the gear transmission and the inner surface of the gearbox had the traces
of damage indicating to rotation caused by the slanted cogs of the conical
cog-wheel of the rotor shaft when the tail rotor broke off.
Tail rotor transmission shaft (like the engines` transmission shafts) had no
distinguishable twisting-shaped deformations indicative of torque.
Right windshield of the helicopter was damaged and heavily cracked, but had
practically retained its form and was fixed in its place. Right-hand cockpit
door`s window was destroyed,
the pieces of the central part of the organic window class could not been
found. Both downward vision windows situating at pilotsŽ feet were
destroyed. Right cockpit door was closed, but heavily deformed and the
airframe surrounding the door was also heavily deformed.
There were crushing deformations caused by pressure on helicopter fuselage
skin on the fuselage right front side, on the lower part of the fuselage and
on the left part of the tail boom.
The doors of right and left main landing gears had slight damages to the
parts far from hinges. HelicopterŽ s nose floating bags had fell out of
their wells and the yellow bags hung attached to the airframe uninflated.
The explosive door links that are used to separate the door linkage upon
deployment of floats were intact.
Emergency Locator Transmitter (ELT) of the helicopter was at its place on
helicopterŽ s tail and its switch was in the "off" position.
HelicopterŽs flight recorder was not damaged and it was removed from the
helicopter.
1.4. Other damage
There was no other damage. Environmental pollution was minimal, since the
amount of petrol used as helicopter fuel was small (approximately 400
litres).
1.5. Personnel information
1.5.1 Pilot-in-command : man, 41years
Licence JAR- (ATPL (H)),
valid until 21.11.2007
Medical fitness JAR class 1, valid until 4.10.2005
Ratings All the necessary ratings were valid
Flight timeIn previous 24 hoursIn previous 30 daysIn previous 90 daysTotal
flight time and number of flights
All aircraft
Helicopter S 76
109 h 48 min
flights
Co-pilot: man, 56 years
Licence (ATPL (H)),
valid until 22.3.2010
Medical fitness JAR, class 1, valid until 3.02.2006.
Ratings All the necessary ratings were valid
Flight time In previous 24 hoursIn previous 30 daysIn previous 90 daysTotal
flight time and number of flights
All aircraft
Helicopter S 76
40 t 06 min
flights
1.6. Aircraft information
Helicopter Sikorsky S76 C+ is a common lay-out helicopter designed and
manufactured in USA, with two turbine engines, two pilots seats and 12
passengers seats.
Passenger seats are situated behind pilots` seats in three rows, 4 seats in
each row.
The helicopter has 4-blade main rotor turning counter-clockwise and a
4-blade tail rotor.
Maximum speed: 155 knots.
Maximum take-off weight of the helicopter is 11700 lb ( 5307 kg).
Actual take-off weight of the helicopter was 10867 lb.
Engines Arriel 2S1, produced in France, Turbomeca plants.
The helicopter is produced in 2000 by Sikorsky Aircraft Corporation, USA.
Registration mark of the helicopter: OH-HCI, date of registration:
21.03.2000.
State of registration: Republic of Finland.
Serial number of the helicopter: 76058.
Airworthiness Certificate of the helicopter was valid until 31.03.2006.
The helicopter has been insured.
1.7. Meteorological information
Weather in the area of the accident was dominated by the north-eastern part
of the low pressure system. The centre of the cyclon was located about 150
km south-west of the accident site and moved to north-east at the speed of
10 km/h. At the time the accident occurred, south-easterly wind 110° 14
knots was blowing on surface in the region of Tallinn Bay. In the layer
1000-2000 ft, south-easterly wind 130°25-30 knots was blowing. Visibility
was 7-8 kilometres. It was raining lightly/moderately, drizzling. The lowest
cloud base of stratus and nimbostratus was 800-1400 ft. The Harku
observatory registered at 12:00 local time (09UTC) isolated cumulonimbus and
light shower. There were no freezing in the lower layer of clouds, freezing
level was 9500 ft. Moderate turbulence was forecasted between layers close
to the surface up to the altitude 4000 ft.
Pressure QNH was 989 hPa. Air temperature was 14°C, dew point was 13°C.
According to meteorological radar, main layer of clouds having effect on the
flight reached from Tallinn to some kilometers distance of the island of
Aegna.
1.8. Aids to navigation
Aids to navigation had no effect on the accident
Communications
The helicopter communicated with Tallinn Control Zone air traffic controller
(Tallinn Tower) on the frequency 120,6 MHz in English language.
Communications had no effect on the occurrence of the accident.
1.10. Heliport information
The accident did not take place on heliport. The helicopter took off from
the City Hall heliport (EECL), situated at Tallinn Bay, 17 ft of sea level.
1.11. Flight recorders
The helicopter was equipped with a combined flight recorder (Penny+Giles
Solid State Combined Voice and Flight Data Recorder), Type 2000,
manufactured in the United Kingdom, which recorded crew voice communications
during the last 30 minutes of the flight and flight data during the last 35
hours of the flight.
The flight recorder was not damaged in the accident, it was removed from the
helicopter and sent to the United Kingdom for the read-out of data. The data
of the both parts of flight recorder were well preserved and they could be
used in investigating into the causes of the accident.
The recordings of Tallinn Secondary Radar were also used in the
investigation. The recordings revealed the abrupt change of helicopter track
(about 50°) to the left, the loss of speed and the preliminary coordinates
of the helicopter wreckage.
1.12. Wreckage and impact information
The helicopter was in the depth of 45 meters on the seabed, the coordinates
of the location were N59°32,546 E 024°43,852.
The part of the helicopter that was found first was the main rotor blade
marked with black colour, which was found floating on the surface close to
the accident site. The blade was relatively slightly damaged and, unlike the
other three blades, had broken off practically next to the hub.
Initial examination of the helicopter with an aim to detect damages was
carried out on the basis of the data of diving machine and video recordings
taken by divers. The quality of the video recordings was bad since, due to
suspended matter, visibility near the helicopter wreckage was approximately
one meter. The helicopter lay on seabed in the reversed ("wheels-up")
position. Landing gear was extracted. Main rotor hub had sunk into the sandy
clay of the seabed. Helicopter tail rotor had broken off the gearbox and was
lying some meters off the helicopter. The ends of main rotor blades and some
other smaller parts of the helicopter were also found. Tail cone of the
helicopter was still attached to the main part of the fuselage, but it had
strong traces of tear at the back of the fuselage. The right-hand cockpit
door window was broken and the right-hand windshield was also damaged.
After the bodies of the victims had been lifted to the surface, the wreckage
of the helicopter was turned so that it would be possible to fix straps to
the rotor hub and the helicopter was lifted to the surface.
It was detected at the initial inspection of the helicopter that the landing
gear of the helicopter was extended, but it had not been extended by the
crew. Out of the four floating bags those situated at the front part of the
helicopter had fallen out of their wells, but they had not been filled with
compressed nitrogen. Two floatingbags that were fixed to the inner sides of
main rotor doors were at their positions. All the compressed nitrogen
bottles were pressurised and the system had not activated. The floats switch
on the overhead console was in the deactivated (i.e. switched off) position.
There were no evidence of fire.
There were no evidence indicating that a bird strike or collision with some
other object could take place in the air.
The tailcone of the helicopter was practically broken off the place were it
was mounted to the fuselage and was hardly attached (practically by electric
cables and hydraulic pipes) to the fuselage. The frames of the back part of
the fuselage were deformed, there were more deformations on the left lower
side of the frames. Before the helicopter was lifted out of the water, the
two tail rotor control cables were unbroken, they broke due to the load
caused by the hanging tail. Due to that load, a tail rotor control rod had
also bent on the cabin.
Right pilot seat was torn off the floor at its two left housings and there
were deformations on the seat back, which indicated loads with right-ahead
effect. Cockpit floor was also deformed and the pedal mechanism of the right
pilot was heavily twisted. Right pilotŽs cyclic was bent ahead near to the
floor.
PilotsŽ headphones were connected to their sockets. There was a through
crack on the case of right pilotŽs headphone.
The inflatable floats system switch at the cockpit ceiling was in the
switched-off position. The switches of electric generators were in the
switched-off position.
Engine condition levers of the overhead panel in the cockpit were in the
following positions: fuel cut-off cocks of the right and left engine (levers
with yellow knobs) were in the normal direct position.
T-handles (fire handles): left engine handle in its normal position, right
engine handle moved back by about a quarter of the travel. Engine power
control levers: the left one practically in the engine-out position and the
right one moved slightly forward of the idle run position.
Landing gear handle was in the "Gear Up " position and the gear emergency
extension handle was not activated.
Helicopter main rotor hub was complete, it had the root ends of four main
rotor blades attached to it, every one of different length (from 30 cm to 1
m).
Both engines of the helicopter, their cowlings and their main output shafts
were undamaged.
Left fuel tank of the helicopter was intact, the right one was damaged.
1.13. Medical and pathological information
As the result of the dissection it was determined that the death of the
victims was caused by drowning.
1.14. Fire
There was no fire.
1.15. Survival aspects
The helicopter was equipped with 4 inflatable floats which would have
enabled the helicopter to float in the normal attitude and would have
ensured the fuselage to stay close to surface in case the helicopter had
turned over. The helicopter was equipped with serviceable inflatable life
jackets under the seats of every occupant of the helicopter.
The speed of the helicopter was not high the moment it hit the water, the
occupants of the helicopter were at that moment rather influenced by high
sink rate and the impact load caused by spinning of the helicopter to the
right. The inertia vector caused by spinning of the helicopter over its
vertical axis had stronger effect on the occupants of the front part of the
helicopter, who suffered more serious injuries.
Fatal factor was suffocation caused by quick sinking of the helicopter.
It was not possible to assess the activation of Emergency Locator
Transmitter (ELT), since radio signals from an aircraft deep under the water
do not reach search and rescue satellite.
'May Day" call by the crew of the helicopter was weak and did not reach the
air traffic services.
Thanks to the air traffic controller who noticed the disappearance of the
radar indication from the screen and a phone-call by an eyewitness, the
information on the accident was received immediately and search operation
was launched in a couple of minutes.
No one of the occupants of the helicopter got out of the helicopter while
the aircraft sank
Passengers of the helicopter had 4-point safety harnesses, the pilots had
5-point safety harnesses.
The safety harnesses of all the occupants of the helicopter were fastened at
the moment the helicopter hit the water. Divers detected that the safety
harnesses of the both pilots were unfastened under the water. The pilot-in
command had (probably unwillingly) got out of the helicopter through the
broken right-hand cockpit door
window and the body of the pilot was found at the distance of 45 meters of
the helicopter after the search operation had been officially closed.
The jettison handle of the left pilot's door was in the upright position,
but the door had not separated from the helicopter. The door was separated
from the helicopter by divers in the course of rescue operation and it was
lifted to the surface on 18 August.
1.16 Tests and research
The investigation commission have had examined:
engines of the helicopter to detect deviations of the helicopter operation
caused by possible malfunctions of the engines. According to unofficially
reported information on the examination of the engines, there are no
observations regarding the operation of engines;
main gearbox of the helicopter to assess the possible brake torque of the
main
gearbox transmission. No malfunctions of the main gearbox were detected as
the result of the examination.
tail gearbox and intermediary gearbox to assess their possible impact on
helicopter`s deviation from its heading. Examination continues.
hydraulic servos and actuators of the helicopter controls, to assess
possible
"overcontrol" caused by the hydraulic servos. Examination continues.
Preliminary acoustic analysis of the cockpit voice recorder was made with an
aim to detect possible characteristic sounds that could be heard in the
cockpit and to receive information on the causes of the accident on the
basis of pilots' communication. Provisional data on the cockpit voice
recordings do not include any direct information indicating to the causes of
emergency situation. Analysis continues.
On the basis of flight recorder data a flight simulation (animation) was
developed to assess the helicopter attitudes and manoeuvres. Simulation
information is under review.
The Investigation Commission intends:
to examine the automatic flight control system data (RDAU);
examination of primary surveillance radar recordings;
to assess floating ability of the helicopter and the rate at which the
helicopter was filled with water;
to arrange necessary simulations on the S-76 C+ flight simulator to assess
the helicopter`s attitude and controllability;
to study pilots' safety harnesses locking system.
1.17. Organisational and management information
The flight was a scheduled passenger flight in controllable airspace. The
take-off and landing are performed under Visual Flight Rules (VFR) and the
en-route flight is performed under Instrument Flight Rules (IFR). There was
no cargo on board.
2. ANALYSIS
2.1 Damage to the helicopter and helicopter attitude on hitting the water
The investigation did not detect any evidence on parts that could have been
separated from the helicopter or could have been damaged in the air. Most of
the damages to the helicopter were caused by the impact of water, some by
hitting the seabottom, others by lifting of it from the seabed and by the
transportation. The parts that had separated from the helicopter were
located quite close to the helicopter at the seabed. The only part of the
helicopter that was located further away (approximately 0.5 km) was the main
rotor blade floating practically in the upright position, which could be
carried away from the accident site by air due to the rotor rotation speed.
It is also likely that it had drifted away due to streams or wind, since the
period between the moment the blade broke off the helicopter and the moment
it was found was about 20 minutes.
No fatigue damage was detected on any part of the helicopter. Damages to the
main rotor blades` cylinders inner surfaces were quite similar for all the
four blades.
Considering the above, the separation of the rotor blade in flight cannot be
considered the cause of the accident by the Investigation Commission.
The helicopter attitude on striking the water could be detected on the basis
of flight recorder data and studying the damages to the helicopter. On
striking the water, the helicopter pitch angle was practically normal. It
had a slight roll (20°) to the right and at the same time it was spinning to
the right over its vertical axis with the rotational speed 1 full turn in
2.5 s. The helicopter tail cone struck the water first, followed immediately
by the front part of the fuselage. The impact of the water to the tail and
the impact load produced a crack to the aircraft skin between the front and
rear part of the helicopter extending almost from the bottom to the top.
That caused the bending of the helicopter tail upwards until it reached the
main rotor plane of rotation and a main rotor blade (with yellow markings)
cut the tail obliquely. The impact of the tail cut off part of the tail
rotor transmission shaft and its cover, which sank close to the wreckage.
The same impact of the blade damaged vertical stabilizer (pylon). The
leading edge of the blade that cut the tail had some small yet clear
deformations and traces of blue colour originating from the helicopter tail.
Main rotor blade edges hit the water probably right of the helicopter on
their forward movement and separated due to the loads caused by brake
torque. The blades' light composite plastic edge fairings, the elements with
highest linear velocity that are not intended to withstand loads, broke off
when the blade edges hit the water.
At the same time, tail rotor encountered the cloud of water created by the
helicopter's hitting the water and, as the result of resultant actions, the
tail rotor was torn off off the tail gearbox.
The condition of the main gearbox and the nature of main and tail rotor
damages exclude the possibility that rotor blade could separate before
hitting the water. The same can be concluded on the basis of flight recorder
recordings.
Since the speed of the helicopter on striking the water was not significant,
most of the damages were due to the sink rate and the spinning of the
helicopter.
2.2 Operation of helicopter equipment
According to the flight recorder data, there were no detectable malfunctions
of helicopter equipment before the emergency situation. Likewise, no
distinct malfunctions of helicopter equipment have been detected during the
period from the occurrence of the emergency situation until the helicopter
hit the water.
2.2.1 Both engines of the helicopter were running without interruption and
produced the torque necessary for rotors` rotation. The torques of both
engines are traceable on flight recorder recordings and they changed
constantly in accordance with the power needed for maintaining rotor speed.
Only approximately 5 seconds before the helicopter hit the water the left
engine was set to idle run (or was switched off, probably by the co-pilot);
as the torque for maintaining rotational speed was applied only to the right
engine from that moment, the torque produced by the right engine started to
increase immediately. Two seconds later (two or three second before the main
rotor blades hit the water) also the torque of the right engine started to
diminish. It is possible that the co-pilot switched the engine off, moving
the T-handle of the right engine to the back position.
2.2.2 Tail rotor continued to rotate and the fracture of the tail gearbox
could only take place when the tail hit the water. The separation of the
tail rotor blades in flight is excluded since, due to the nature of the
helicopter`s design, the imbalance caused by the separation of one blade
should have separated also the blade opposite to it together with their
linking part by the centrifugal force arising from the rotation of the
rotor. The fact that the linking parts of the both rotor blade couples had
remained attached to the tail rotor hub indicates that, although only one
blade of the four tail rotor blades had remained attached to the hub, the
separation of the three blades must have taken place immediately before the
tail rotor rotation was definitively stopped on hitting the water. At the
same time, the power necessary for the fracture of tail rotor gearbox could
only originate from the tail rotor that rotated at normal speed.
2.2.3. The malfunction of helicopter main gearbox, which could have caused
helicopter`s abrupt retardation that could lead to uncontrollability is
excluded on the basis of the results of main gearbox examination.
2.3 Development of uncontrollable attitude
The helicopter was practically uncontrollable after the emergency situation
occurred at the moment 0. The drastically increased vertical acceleration
(up to +3G) and longitudinal acceleration (actually helicopter`s
deceleration - 0,3 G) was followed by active turn to left, which later
developed into right turn and constant spinning to the right. In spite of
pilot s acting with controls, he was not able to resume control due to low
speed and great changes in attitude.
So far, the Investigation Commission has not been able to find out the
primary cause for developing the uncontrollable attitude by the helicopter.
3. CONCLUSIONS
3.1 Preliminary assessment of factual information:
The helicopter was destroyed on hitting the water and sank on a scheduled
passenger flight at daytime;
Helicopter crew had the required licenses and ratings necessary for the
flight;
Helicopter was maintained in accordance with applicable requirements;
Helicopter Airworthiness Certificate was valid and the helicopter had the
equipment, fuel and lubricants necessary for the flight;
Helicopter mass and the centre of gravity were within the required
limitations;
There were no prior warnings on equipment malfunctions before the
emergency situation occurred;
Helicopter engines remained operable until the end of the flight;
Meteorological conditions were in accordance with the requirements for the
flight;
Damages to the helicopter were caused by the impact of the water;
Helicopter sank quickly after hitting the water and no one of the occupants
of
the helicopter was able to get out of the aircraft.
Search and rescue operation started with minimum delay and there were no
possibilities to rescue the occupants of the helicopter.
3.2 Causes of the accident:
The helicopter encountered an emergency situation in the third minute of the
flight at the altitude 1500 fl and speed 130 knots. The emergency situation
caused helicopter's significant deviation from normal flight
characteristics, which ultimately led to uncontrollable fall.
The Investigation Commission will continue the investigation to find out the
causes of the accident.
4. SAFETY RECOMMENDATIONS
On the basis of preliminary analysis and material, the Investigation
Commission cannot make any flight safety recommendations so far.
Members of the Investigation Commission: Taivo Kivistik
Tõnu Ader
Oleg Harlamov
Mati Iila
Jaanus Ojamets
Toomas Kasemaa
Tiit Kaurla
Aleksander Dintsenko
12 September 2005
lähiaikoina:
Luettuna ao. helik.onnettomuusselvitys tuntuu kiehtovasti mystiseltä, koska
siinä täysin "sivuutetaan" ennen nollahetkeä ollut 37-sekunnin 'emergency
situation', vaikka myöhemmin mainitaan ettei siinä (muka?) ollut mitään joka
auttaisi syyn selvittämisessä.
Selvästi kirjailijan mielikuvitus alkaa lentää: mitä oikein tapahtui,
murhattiinko joku, tekikö joku itsarin, ...
Kirjoittais ny joku vaikka tänne novellin "37 SEKUNTIA"...
tv Perttu Pulkkinen, jkl
Ps. toki todellisuudessa varmaan syy raporin salamyhkäisyyteen on siinä,
että siinä vain poissuljetaan muita syitä eikä ehdotella mitään, mutta eikö
tällaisista aineksista hyvät dekkarit hiukan liioittelemalla saa
käyttövoimansa normaalistikin?
***********************************************************************
PRELIMINARY REPORT
AIRCRAFT ACCIDENT INVESTIGATION COMMISSION
Aircraft Accident involving helicopter Sikorsky S76 C+
Registration mark OH - HCI
Tallinn Bay, 10 August 2005
TALLINN
2005
SYNOPSIS
On 10 August 2005 at 12:45 local time, an accident occurred with helicopter
Sikorsky S76C+, registration OH - HCI, on its scheduled passenger service
from Tallinn to Helsinki. All the 14 occupants of the helicopter were killed
in the accident, the helicopter was destroyed. The helicopter hit the water
2 km southwest of the island of Aegna. i.e. at the 12 km distance of the
take-off place at the City Hall heliport and sank to the depth of 45 meters.
None of the occupants of the helicopter were found in the course of search
and rescue operation that started immediately. Only a light trace of oil
pollution and the helicopter main rotor blade floating on the surface of the
sea were found close to the accident site.
The wreckage of the helicopter was found 5 hours later with the help of
robot. The operation of rescuing the bodies of the victims of the accident
started the next day. Divers succeeded in lifting the bodies of all the 13
victims who had occupied the helicopter in 24 hours. The body of one of the
victims (pilot-in-command of the helicopter) was found 15 days later in the
course of additional search operation approximately 45 off the place were
the helicopter sank.
The wreckage of the helicopter was lifted to the surface on the third day
after the accident (13.08.2005.a.) and was it taken to the hangar on Tallinn
airport for the purpose of examination
On the day of the accident, a 8-member commission for investigating into the
causes of the accident was appointed under the decree of the Minister of
Economic Affairs and Communications. The composition of the commission is as
follows:
Chairman:
Taivo Kivistik Deputy Secretary General, Ministry of Economic Affairs and
Communications
Deputy Chairman:
Tõnu Ader Executive Officer, Emergency Management Department, Ministry of
Economic Affairs and Communications
Members of the Commission:
Oleg Harlamov Counsellor to the Minister, Ministry of Economic Affairs and
Communications
Mati Iila Counsellor, Emergency Management Department, Ministry of Economic
Affairs and Communications
Tiit Kaurla- Executive Officer, European Union and International Cooperation
Department, Ministry of Economic Affairs and Communications
Toomas Kasemaa Head of the Bureau of Border Guard Policy, Internal Security
Policy Department, Ministry of the Interior
Aleksander Dintsenko Senior Inspector, Department of Air Traffic Services
and Aerodromes, Civil Aviation Administration
Jaanus Ojamets Senior Inspector, Flight Operations Department, Civil
Aviation Administration
USA as a State of Manufacture and the State of Design of the helicopter
appointed Aircraft Accident Investigator Ms Lorenda E Wardi, National
Transportation Safety Board (NTSB), as its official representative at the
Commission.
Finland as the State of Operator appointed Aircraft Accident Investigator at
the FinlandŽs Aircraft Accident Investigation Centre, Mr Hannu Melaranta as
its official representative at the Commission.
Preliminary report of the aircraft accident investigation was signed on 12
September 2005.
BODY
1. FACTUAL INFORMATION
History of the flight
Helicopter Sikorsky S76C+ with registration mark OH - HCI, with 12
passengers and 2 pilots as crew members on board, departed from Tallinn City
Hall heliport on 10 August 2005 at 12:39 p.m. local time (i.e. at 09:39 UTC)
and started its normal flight on the route to Helsinki. The flight on the
route usually lasts 18 minutes, the distance is 80 km.
The crew of the helicopter, consisting of Finnish nationals, had performed 5
landings on Tallinn City Hall heliport that day. Weather was suitable for
the flight and another take-off (i.e. the fifth one) at the direction of
Helsinki took place as usual, not to mention the delay from schedule due to
the delays of previous flights. 6 nationals of Finland, 4 nationals of
Estonia and 2 nationals of USA, including 7 women and 5 men, were on board
of the helicopter as passengers. Before take-off, automatic passenger
briefing was started in Finnish, Estonian and English languages. There were
no problems with completing pre-flight and after-take-off checklists.
Pilot-in-command sitting on the right seat was the pilot flying. After the
take-off on heading 110°, the helicopter turned left and continued the
flight on heading 355° with acceleration and climb. Air Traffic Controller
of the Tallinn Tower was reported that the helicopter was airborne.
After reaching the altitude of 1500 ft (according to the flight recorder
2000 ft standard atmosphere) and the speed of 130 knots and approaching the
border of Tallinn Airport Control Zone, the crew assessed the cloud
conditions ahead and prepared to climb to the altitude of 2000 ft or higher.
After telling the co-pilot that he was going to add some power, the
pilot-in-command started to raise the collective. Energetic raising of the
collective took place 5 seconds after that moment. Until that moment, the
flight had proceeded as normal, but starting from that moment (hereinafter
"moment 0"), an emergency situation occurred, which lasted for 37 seconds
and ended with helicopter` s striking the water. According to the flight
recorder recording, the raising of the collective was followed by active
pulling of the cyclic approximately half of the maximum travel and immediate
(a second later) fully forward movement of the cyclic for a very short
period . The pulling of the cyclic was followed, according to the cockpit
voice recorder recordings, by the exclamation by the pilot-in-command and, a
warning signal. At the same time, according to the flight recorder
recordings, the increase of vertical acceleration in 1.5 seconds from + 1G
to +3 G took place.
When 1.5 seconds had passed from the moment 0, the helicopter was in the
following attitude:
pitch had increased to 40° and continued to increase;
roll to the left was 40° and continued to increase;
heading had changed from 355° to 320°, i.e. the front part of the helicopter
had turned left by 35° comparing to the initial heading and the turn to the
left continued for more 4 seconds.
The helicopter lost speed, but at the same time climbed for approximately
200 ft (up to the altitude 1700 ft) and maintained this altitude in about 10
seconds, after which the altitude started to diminish with unstable rate of
descent. During the next half a minute, the helicopter changed its attitude
irregularly, to which the crew reacted by acting with helicopter controls.
After the occurrence of emergency situation the cockpit voice recorder had
not recorded any comments by the crew that could explain the causes of the
occurrence and the helicopter`s unusual attitude. The only clearly
distinguishable phrases were three fast and weakly audible "May Day" calls
by the pilot-in-command and a question by the co-pilot "The tail has gone?"
Air Traffic Controller in Tallinn Tower, who was about to communicate to the
helicopter their take-off time and the information to contact the air
traffic controller of Tallinn approach area on the frequency 127,9 MHz,
noticed the abrupt change of helicopter`s heading and the following loss of
altitude as well as the disappearance of the radar indication from the
screen.
The last seconds of the accident were witnessed by a captain of a pilot boat
in port approximately 3 km away from the accident site. The helicopter
attracted captain`s attention because of some consecutive loud banging
sounds. He called immediately to the emergency service and contacted a pilot
boat that was close to the accident site. The boat arrived at the accident
site about ten minutes after the accident.
At the same time (at 12:55 pm) the search and rescue helicopter of the
Border Guard Aviation Group took off from Tallinn airport and arrived at the
accident site approximately 20 minutes after the accident.
According to the recordings of flight recorder, the helicopter turned first
left up to the heading 250° (at the moment 4 s) after which the helicopter`s
heading started to increase again (the helicopter turned right). Spinning of
the helicopter to the right continued till it hit the water. In
approximately half a minute, the helicopter made 13 full turns and hit the
water on heading 360º.
The collective of the helicopter was in the position of active climb during
the period from the moment 0 to 3 seconds. Until the moment 9 s, it
maintained the position close to that of maximum climb. After that the
collective abruptly resumed the position it had before the moment 0. Later,
the collective continued to move downward and was close to lowest position
at the last seconds of the flight.
Helicopter rotor revolutions were between 100% and 110% most of the time,
except for the period from 4 to 12 seconds, when the rotor speed was
significantly lower than normal and fell for a moment (at the moment 6 s) to
70%.
Both engines of the helicopter were running and producing the power
necessary for rotors` rotation.
The helicopter continued to spin irregularly and finally hit the water and
turned immediately over.
Emergency floatation system did not activate.
The helicopter was quickly filled with water and sank into the sea in
approximately 10 seconds.
1.2. Injuries to persons
All the occupants of the helicopter were killed.
Damage to aircraft
The aircraft had sunk 45 m into the water. One the main rotor blade had
injured tail boom and cut through the mechanic transmission of the tail
rotor, but the tail cone of the helicopter had retained its integrity. As
the result of the impact of the blade, the transmission shaft and its cover
had removed to the extent of about 1 meter. The parts that had torn off were
lying at about ten metres` distance from the helicopter wreckage on the
seabed and they were rescued by divers.
Main rotor hub was in its normal position and root parts of all the four
main rotor blades had similar damages, only the length of the parts of the
blades attached to the hub was varying. Blades vibration absorbers (dampers)
had also broken off.
Panels of the stabilizer had damages indicative of the impact of hitting the
water, the right panel had separated from the tail. The left part of the
tail gearbox together with tail rotor had broken off its main part and were
lying apart from the helicopter. However, there were no detectable damages
to the gear transmission and the inner surface of the gearbox had the traces
of damage indicating to rotation caused by the slanted cogs of the conical
cog-wheel of the rotor shaft when the tail rotor broke off.
Tail rotor transmission shaft (like the engines` transmission shafts) had no
distinguishable twisting-shaped deformations indicative of torque.
Right windshield of the helicopter was damaged and heavily cracked, but had
practically retained its form and was fixed in its place. Right-hand cockpit
door`s window was destroyed,
the pieces of the central part of the organic window class could not been
found. Both downward vision windows situating at pilotsŽ feet were
destroyed. Right cockpit door was closed, but heavily deformed and the
airframe surrounding the door was also heavily deformed.
There were crushing deformations caused by pressure on helicopter fuselage
skin on the fuselage right front side, on the lower part of the fuselage and
on the left part of the tail boom.
The doors of right and left main landing gears had slight damages to the
parts far from hinges. HelicopterŽ s nose floating bags had fell out of
their wells and the yellow bags hung attached to the airframe uninflated.
The explosive door links that are used to separate the door linkage upon
deployment of floats were intact.
Emergency Locator Transmitter (ELT) of the helicopter was at its place on
helicopterŽ s tail and its switch was in the "off" position.
HelicopterŽs flight recorder was not damaged and it was removed from the
helicopter.
1.4. Other damage
There was no other damage. Environmental pollution was minimal, since the
amount of petrol used as helicopter fuel was small (approximately 400
litres).
1.5. Personnel information
1.5.1 Pilot-in-command : man, 41years
Licence JAR- (ATPL (H)),
valid until 21.11.2007
Medical fitness JAR class 1, valid until 4.10.2005
Ratings All the necessary ratings were valid
Flight timeIn previous 24 hoursIn previous 30 daysIn previous 90 daysTotal
flight time and number of flights
All aircraft
Helicopter S 76
109 h 48 min
flights
Co-pilot: man, 56 years
Licence (ATPL (H)),
valid until 22.3.2010
Medical fitness JAR, class 1, valid until 3.02.2006.
Ratings All the necessary ratings were valid
Flight time In previous 24 hoursIn previous 30 daysIn previous 90 daysTotal
flight time and number of flights
All aircraft
Helicopter S 76
40 t 06 min
flights
1.6. Aircraft information
Helicopter Sikorsky S76 C+ is a common lay-out helicopter designed and
manufactured in USA, with two turbine engines, two pilots seats and 12
passengers seats.
Passenger seats are situated behind pilots` seats in three rows, 4 seats in
each row.
The helicopter has 4-blade main rotor turning counter-clockwise and a
4-blade tail rotor.
Maximum speed: 155 knots.
Maximum take-off weight of the helicopter is 11700 lb ( 5307 kg).
Actual take-off weight of the helicopter was 10867 lb.
Engines Arriel 2S1, produced in France, Turbomeca plants.
The helicopter is produced in 2000 by Sikorsky Aircraft Corporation, USA.
Registration mark of the helicopter: OH-HCI, date of registration:
21.03.2000.
State of registration: Republic of Finland.
Serial number of the helicopter: 76058.
Airworthiness Certificate of the helicopter was valid until 31.03.2006.
The helicopter has been insured.
1.7. Meteorological information
Weather in the area of the accident was dominated by the north-eastern part
of the low pressure system. The centre of the cyclon was located about 150
km south-west of the accident site and moved to north-east at the speed of
10 km/h. At the time the accident occurred, south-easterly wind 110° 14
knots was blowing on surface in the region of Tallinn Bay. In the layer
1000-2000 ft, south-easterly wind 130°25-30 knots was blowing. Visibility
was 7-8 kilometres. It was raining lightly/moderately, drizzling. The lowest
cloud base of stratus and nimbostratus was 800-1400 ft. The Harku
observatory registered at 12:00 local time (09UTC) isolated cumulonimbus and
light shower. There were no freezing in the lower layer of clouds, freezing
level was 9500 ft. Moderate turbulence was forecasted between layers close
to the surface up to the altitude 4000 ft.
Pressure QNH was 989 hPa. Air temperature was 14°C, dew point was 13°C.
According to meteorological radar, main layer of clouds having effect on the
flight reached from Tallinn to some kilometers distance of the island of
Aegna.
1.8. Aids to navigation
Aids to navigation had no effect on the accident
Communications
The helicopter communicated with Tallinn Control Zone air traffic controller
(Tallinn Tower) on the frequency 120,6 MHz in English language.
Communications had no effect on the occurrence of the accident.
1.10. Heliport information
The accident did not take place on heliport. The helicopter took off from
the City Hall heliport (EECL), situated at Tallinn Bay, 17 ft of sea level.
1.11. Flight recorders
The helicopter was equipped with a combined flight recorder (Penny+Giles
Solid State Combined Voice and Flight Data Recorder), Type 2000,
manufactured in the United Kingdom, which recorded crew voice communications
during the last 30 minutes of the flight and flight data during the last 35
hours of the flight.
The flight recorder was not damaged in the accident, it was removed from the
helicopter and sent to the United Kingdom for the read-out of data. The data
of the both parts of flight recorder were well preserved and they could be
used in investigating into the causes of the accident.
The recordings of Tallinn Secondary Radar were also used in the
investigation. The recordings revealed the abrupt change of helicopter track
(about 50°) to the left, the loss of speed and the preliminary coordinates
of the helicopter wreckage.
1.12. Wreckage and impact information
The helicopter was in the depth of 45 meters on the seabed, the coordinates
of the location were N59°32,546 E 024°43,852.
The part of the helicopter that was found first was the main rotor blade
marked with black colour, which was found floating on the surface close to
the accident site. The blade was relatively slightly damaged and, unlike the
other three blades, had broken off practically next to the hub.
Initial examination of the helicopter with an aim to detect damages was
carried out on the basis of the data of diving machine and video recordings
taken by divers. The quality of the video recordings was bad since, due to
suspended matter, visibility near the helicopter wreckage was approximately
one meter. The helicopter lay on seabed in the reversed ("wheels-up")
position. Landing gear was extracted. Main rotor hub had sunk into the sandy
clay of the seabed. Helicopter tail rotor had broken off the gearbox and was
lying some meters off the helicopter. The ends of main rotor blades and some
other smaller parts of the helicopter were also found. Tail cone of the
helicopter was still attached to the main part of the fuselage, but it had
strong traces of tear at the back of the fuselage. The right-hand cockpit
door window was broken and the right-hand windshield was also damaged.
After the bodies of the victims had been lifted to the surface, the wreckage
of the helicopter was turned so that it would be possible to fix straps to
the rotor hub and the helicopter was lifted to the surface.
It was detected at the initial inspection of the helicopter that the landing
gear of the helicopter was extended, but it had not been extended by the
crew. Out of the four floating bags those situated at the front part of the
helicopter had fallen out of their wells, but they had not been filled with
compressed nitrogen. Two floatingbags that were fixed to the inner sides of
main rotor doors were at their positions. All the compressed nitrogen
bottles were pressurised and the system had not activated. The floats switch
on the overhead console was in the deactivated (i.e. switched off) position.
There were no evidence of fire.
There were no evidence indicating that a bird strike or collision with some
other object could take place in the air.
The tailcone of the helicopter was practically broken off the place were it
was mounted to the fuselage and was hardly attached (practically by electric
cables and hydraulic pipes) to the fuselage. The frames of the back part of
the fuselage were deformed, there were more deformations on the left lower
side of the frames. Before the helicopter was lifted out of the water, the
two tail rotor control cables were unbroken, they broke due to the load
caused by the hanging tail. Due to that load, a tail rotor control rod had
also bent on the cabin.
Right pilot seat was torn off the floor at its two left housings and there
were deformations on the seat back, which indicated loads with right-ahead
effect. Cockpit floor was also deformed and the pedal mechanism of the right
pilot was heavily twisted. Right pilotŽs cyclic was bent ahead near to the
floor.
PilotsŽ headphones were connected to their sockets. There was a through
crack on the case of right pilotŽs headphone.
The inflatable floats system switch at the cockpit ceiling was in the
switched-off position. The switches of electric generators were in the
switched-off position.
Engine condition levers of the overhead panel in the cockpit were in the
following positions: fuel cut-off cocks of the right and left engine (levers
with yellow knobs) were in the normal direct position.
T-handles (fire handles): left engine handle in its normal position, right
engine handle moved back by about a quarter of the travel. Engine power
control levers: the left one practically in the engine-out position and the
right one moved slightly forward of the idle run position.
Landing gear handle was in the "Gear Up " position and the gear emergency
extension handle was not activated.
Helicopter main rotor hub was complete, it had the root ends of four main
rotor blades attached to it, every one of different length (from 30 cm to 1
m).
Both engines of the helicopter, their cowlings and their main output shafts
were undamaged.
Left fuel tank of the helicopter was intact, the right one was damaged.
1.13. Medical and pathological information
As the result of the dissection it was determined that the death of the
victims was caused by drowning.
1.14. Fire
There was no fire.
1.15. Survival aspects
The helicopter was equipped with 4 inflatable floats which would have
enabled the helicopter to float in the normal attitude and would have
ensured the fuselage to stay close to surface in case the helicopter had
turned over. The helicopter was equipped with serviceable inflatable life
jackets under the seats of every occupant of the helicopter.
The speed of the helicopter was not high the moment it hit the water, the
occupants of the helicopter were at that moment rather influenced by high
sink rate and the impact load caused by spinning of the helicopter to the
right. The inertia vector caused by spinning of the helicopter over its
vertical axis had stronger effect on the occupants of the front part of the
helicopter, who suffered more serious injuries.
Fatal factor was suffocation caused by quick sinking of the helicopter.
It was not possible to assess the activation of Emergency Locator
Transmitter (ELT), since radio signals from an aircraft deep under the water
do not reach search and rescue satellite.
'May Day" call by the crew of the helicopter was weak and did not reach the
air traffic services.
Thanks to the air traffic controller who noticed the disappearance of the
radar indication from the screen and a phone-call by an eyewitness, the
information on the accident was received immediately and search operation
was launched in a couple of minutes.
No one of the occupants of the helicopter got out of the helicopter while
the aircraft sank
Passengers of the helicopter had 4-point safety harnesses, the pilots had
5-point safety harnesses.
The safety harnesses of all the occupants of the helicopter were fastened at
the moment the helicopter hit the water. Divers detected that the safety
harnesses of the both pilots were unfastened under the water. The pilot-in
command had (probably unwillingly) got out of the helicopter through the
broken right-hand cockpit door
window and the body of the pilot was found at the distance of 45 meters of
the helicopter after the search operation had been officially closed.
The jettison handle of the left pilot's door was in the upright position,
but the door had not separated from the helicopter. The door was separated
from the helicopter by divers in the course of rescue operation and it was
lifted to the surface on 18 August.
1.16 Tests and research
The investigation commission have had examined:
engines of the helicopter to detect deviations of the helicopter operation
caused by possible malfunctions of the engines. According to unofficially
reported information on the examination of the engines, there are no
observations regarding the operation of engines;
main gearbox of the helicopter to assess the possible brake torque of the
main
gearbox transmission. No malfunctions of the main gearbox were detected as
the result of the examination.
tail gearbox and intermediary gearbox to assess their possible impact on
helicopter`s deviation from its heading. Examination continues.
hydraulic servos and actuators of the helicopter controls, to assess
possible
"overcontrol" caused by the hydraulic servos. Examination continues.
Preliminary acoustic analysis of the cockpit voice recorder was made with an
aim to detect possible characteristic sounds that could be heard in the
cockpit and to receive information on the causes of the accident on the
basis of pilots' communication. Provisional data on the cockpit voice
recordings do not include any direct information indicating to the causes of
emergency situation. Analysis continues.
On the basis of flight recorder data a flight simulation (animation) was
developed to assess the helicopter attitudes and manoeuvres. Simulation
information is under review.
The Investigation Commission intends:
to examine the automatic flight control system data (RDAU);
examination of primary surveillance radar recordings;
to assess floating ability of the helicopter and the rate at which the
helicopter was filled with water;
to arrange necessary simulations on the S-76 C+ flight simulator to assess
the helicopter`s attitude and controllability;
to study pilots' safety harnesses locking system.
1.17. Organisational and management information
The flight was a scheduled passenger flight in controllable airspace. The
take-off and landing are performed under Visual Flight Rules (VFR) and the
en-route flight is performed under Instrument Flight Rules (IFR). There was
no cargo on board.
2. ANALYSIS
2.1 Damage to the helicopter and helicopter attitude on hitting the water
The investigation did not detect any evidence on parts that could have been
separated from the helicopter or could have been damaged in the air. Most of
the damages to the helicopter were caused by the impact of water, some by
hitting the seabottom, others by lifting of it from the seabed and by the
transportation. The parts that had separated from the helicopter were
located quite close to the helicopter at the seabed. The only part of the
helicopter that was located further away (approximately 0.5 km) was the main
rotor blade floating practically in the upright position, which could be
carried away from the accident site by air due to the rotor rotation speed.
It is also likely that it had drifted away due to streams or wind, since the
period between the moment the blade broke off the helicopter and the moment
it was found was about 20 minutes.
No fatigue damage was detected on any part of the helicopter. Damages to the
main rotor blades` cylinders inner surfaces were quite similar for all the
four blades.
Considering the above, the separation of the rotor blade in flight cannot be
considered the cause of the accident by the Investigation Commission.
The helicopter attitude on striking the water could be detected on the basis
of flight recorder data and studying the damages to the helicopter. On
striking the water, the helicopter pitch angle was practically normal. It
had a slight roll (20°) to the right and at the same time it was spinning to
the right over its vertical axis with the rotational speed 1 full turn in
2.5 s. The helicopter tail cone struck the water first, followed immediately
by the front part of the fuselage. The impact of the water to the tail and
the impact load produced a crack to the aircraft skin between the front and
rear part of the helicopter extending almost from the bottom to the top.
That caused the bending of the helicopter tail upwards until it reached the
main rotor plane of rotation and a main rotor blade (with yellow markings)
cut the tail obliquely. The impact of the tail cut off part of the tail
rotor transmission shaft and its cover, which sank close to the wreckage.
The same impact of the blade damaged vertical stabilizer (pylon). The
leading edge of the blade that cut the tail had some small yet clear
deformations and traces of blue colour originating from the helicopter tail.
Main rotor blade edges hit the water probably right of the helicopter on
their forward movement and separated due to the loads caused by brake
torque. The blades' light composite plastic edge fairings, the elements with
highest linear velocity that are not intended to withstand loads, broke off
when the blade edges hit the water.
At the same time, tail rotor encountered the cloud of water created by the
helicopter's hitting the water and, as the result of resultant actions, the
tail rotor was torn off off the tail gearbox.
The condition of the main gearbox and the nature of main and tail rotor
damages exclude the possibility that rotor blade could separate before
hitting the water. The same can be concluded on the basis of flight recorder
recordings.
Since the speed of the helicopter on striking the water was not significant,
most of the damages were due to the sink rate and the spinning of the
helicopter.
2.2 Operation of helicopter equipment
According to the flight recorder data, there were no detectable malfunctions
of helicopter equipment before the emergency situation. Likewise, no
distinct malfunctions of helicopter equipment have been detected during the
period from the occurrence of the emergency situation until the helicopter
hit the water.
2.2.1 Both engines of the helicopter were running without interruption and
produced the torque necessary for rotors` rotation. The torques of both
engines are traceable on flight recorder recordings and they changed
constantly in accordance with the power needed for maintaining rotor speed.
Only approximately 5 seconds before the helicopter hit the water the left
engine was set to idle run (or was switched off, probably by the co-pilot);
as the torque for maintaining rotational speed was applied only to the right
engine from that moment, the torque produced by the right engine started to
increase immediately. Two seconds later (two or three second before the main
rotor blades hit the water) also the torque of the right engine started to
diminish. It is possible that the co-pilot switched the engine off, moving
the T-handle of the right engine to the back position.
2.2.2 Tail rotor continued to rotate and the fracture of the tail gearbox
could only take place when the tail hit the water. The separation of the
tail rotor blades in flight is excluded since, due to the nature of the
helicopter`s design, the imbalance caused by the separation of one blade
should have separated also the blade opposite to it together with their
linking part by the centrifugal force arising from the rotation of the
rotor. The fact that the linking parts of the both rotor blade couples had
remained attached to the tail rotor hub indicates that, although only one
blade of the four tail rotor blades had remained attached to the hub, the
separation of the three blades must have taken place immediately before the
tail rotor rotation was definitively stopped on hitting the water. At the
same time, the power necessary for the fracture of tail rotor gearbox could
only originate from the tail rotor that rotated at normal speed.
2.2.3. The malfunction of helicopter main gearbox, which could have caused
helicopter`s abrupt retardation that could lead to uncontrollability is
excluded on the basis of the results of main gearbox examination.
2.3 Development of uncontrollable attitude
The helicopter was practically uncontrollable after the emergency situation
occurred at the moment 0. The drastically increased vertical acceleration
(up to +3G) and longitudinal acceleration (actually helicopter`s
deceleration - 0,3 G) was followed by active turn to left, which later
developed into right turn and constant spinning to the right. In spite of
pilot s acting with controls, he was not able to resume control due to low
speed and great changes in attitude.
So far, the Investigation Commission has not been able to find out the
primary cause for developing the uncontrollable attitude by the helicopter.
3. CONCLUSIONS
3.1 Preliminary assessment of factual information:
The helicopter was destroyed on hitting the water and sank on a scheduled
passenger flight at daytime;
Helicopter crew had the required licenses and ratings necessary for the
flight;
Helicopter was maintained in accordance with applicable requirements;
Helicopter Airworthiness Certificate was valid and the helicopter had the
equipment, fuel and lubricants necessary for the flight;
Helicopter mass and the centre of gravity were within the required
limitations;
There were no prior warnings on equipment malfunctions before the
emergency situation occurred;
Helicopter engines remained operable until the end of the flight;
Meteorological conditions were in accordance with the requirements for the
flight;
Damages to the helicopter were caused by the impact of the water;
Helicopter sank quickly after hitting the water and no one of the occupants
of
the helicopter was able to get out of the aircraft.
Search and rescue operation started with minimum delay and there were no
possibilities to rescue the occupants of the helicopter.
3.2 Causes of the accident:
The helicopter encountered an emergency situation in the third minute of the
flight at the altitude 1500 fl and speed 130 knots. The emergency situation
caused helicopter's significant deviation from normal flight
characteristics, which ultimately led to uncontrollable fall.
The Investigation Commission will continue the investigation to find out the
causes of the accident.
4. SAFETY RECOMMENDATIONS
On the basis of preliminary analysis and material, the Investigation
Commission cannot make any flight safety recommendations so far.
Members of the Investigation Commission: Taivo Kivistik
Tõnu Ader
Oleg Harlamov
Mati Iila
Jaanus Ojamets
Toomas Kasemaa
Tiit Kaurla
Aleksander Dintsenko
12 September 2005