The Malaysian investigation’s findings
Published on: Thursday, April 13, 2023
The aircraft was on a flight from Labuan to Kota Kinabalu with one pilot and ten passengers on board.
After having been processed by the Kota Kinabalu air craft control the aircraft was cleared to final to land on runway 20.
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On finals after having failed to acknowledge two landing clearance given by the tower controller the aircraft went into a spin and struck the sea bed in a steep nose attitude killing the pilot and all ten passengers on board.
The aircraft was substantiality damaged beyond repair.
The report concludes that the probable cause of the accident was due to a Centre of Gravity position well outside the aft limit which caused the control column to run out of forward range as the nose pitched up when the flaps passed through 25c on the final approach to land.
FINAL REPORT
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ACCIDENT TO NOMAD N22A 9M-ATZ KOTA KINABALU
6th JUNE, 1976
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INVESTIGATION TEAM
1. Col. (U) Omar bin Saman –Chief Inspector of Accidents
Director of Flight Operations Civil Aviation Department
2. Lt. Col. (U) Su Kien Chin. Research & Development Department. Royal Malaysian Air Force.
3. Lt. Col. (U) Lau Chong See. Staff Officer Engineering
Air Headquarters, Royal Malaysian Air Force
4. E.V.Read Flight Calibration Unit Civil Aviation Department
5. R.C. Williams/ Airworthiness Unit Civil Aviation Department.
6. P.E. Choquenot. Accredited Representative Department of Transport, Australia
7. C. Sutherland. Accredited Representative Department of Transport Australia
In Attendance as Required But not in the team
1. S.G Pearce ) Chief Test Pilot) Govt Aircraft Factories Australia
2. D.R. Hooper. Chief Designer
TERM OF REFERENCE
To determine the facts, conditions and circumstances pertaining to the accident with a view to establishing the probable cause thereof, so that appropriate steps may be taken to prevent a recurrence of the accident and the factors which led to it.
JABATAN PENERBANGAN AWAM
KEMENTERIAN PERHUBUNGAN
KUALA LUMPUR
AIRCRAFT ACCIDENT
REPORT NO: 1/76
AIRCRAFT TYPE & REGISTRATION: Nomad N22B, 9M-ATZ
ENGINE: Two Allison 250-B-17B
REGISTERED OWNER: Penerbangan Sabah, Kota Kinabalu, Sabah.
CREW: Aircraft Commander, fatally injured
PASSENGERS: Ten, all fatally injured
PLACE OF ACCIDENT: Approximately 1 nautical mile on the extended Centre line of Runway 20, Kota Kinabalu Airport.
DATE & TIME: 6 June, 1976 at 1542 hours. All times in this report are local time Sabah/Sarawak.
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SUMMARY
The aircraft was on a flight from Labuan to Kota Kinabalu with one pilot and ten passengers on board. After having been processed by the Kota Kinabalu air craft control the aircraft was cleared to final to land on runway 20. On finals after having failed to acknowledge two landing clearance given by the tower controller the aircraft went into a spin and struck the sea bed in a steep nose attitude killing the pilot and all ten passengers on board. The aircraft was substantiality damaged beyond repair.
The report concludes that the probable cause of the accident was due to a Centre of Gravity position well outside the aft limit which caused the control column to run out of forward range as the nose pitched up when the flaps passed through 25c on the final approach to land.
Investigation
1. 1 History of the Flight
At the time of the accident the aircraft, 9M-ATZ, together with another “Nomad” 9M-AUA was engaged on a Government Charter to convey V.I.P personnel from Labuan to Kota Kinabalu, and the pilot-in-command of 9M-ATZ was the only crew member on board. The aircraft was positioned at Labuan by another Penerbangan Sabah pilot on the previous day. Both the aircraft commander and the aircraft remained in Labuan overnight in preparation for a series of Flights between Labuan and Kota Kinabalu which were to be carried out on the day of the accident.
On the first flight on 6th Juno, the aircraft departed from Labuan 0635 hours and arrived at Kota Kinabalu at 0705 hours. It was refuelled and deported for Labuan at 1035 hours arriving there at 1105 hours. The aircraft then departed from Labuan at 1115 hours and arrived at Kota Kinabalu at 1145 hours where it was again refuelled. These flights were apparently carried out in a normal routine manner and the pilot did not report any aircraft unserviceability which required attention by maintenance engineers.
During the periods when the aircraft was on the ground at Kota Kinabalu, the aircraft commander spoke to a number of acquaintances and stated that he was tired and that he was suffering from a mild stomach upset as a result, he believed, of food he had eaten on the previous night at Labuan.
The aircraft departed from Kota Kinabalu for Labuan at 1310 hours, and arrived at 1340 hours. Cn this flight, at the invitation of the aircraft commander, another pilot employed by Penerbengan Sabah occupied the right hand co-pilot seat. This pilot was not endorsed on the Nomad and he was not involved in the operation of the aircraft. He has reported that the flight was normal in all respects.
After arriving at Labuan, a quantity of baggage was delivered to the aircraft. The aircraft commander, loaded some of the baggage into the nose baggage compartment while the other pilot was instructed to load the remaining baggage into the rear baggage compartment. The aircraft was then taxied and parked at the VIP terminal to await the arrival of the passengers.
When the passengers arrived at the aircraft, it was found that ten persons wished to travel to Kota Kinabalu and as the aircraft was equipped with only nine passenger seats, the pilot who had accompanied the aircraft to Labuan was off-loaded to await the next flight and a passenger occupied the right-hand co-pilot seat.
Shortly before the take-off of 9M-ATZ, the other “Nomad” 9M-AUA departed with one crew member and twelve passengers with ultimate destination Kota Kinabalu via Kudat.
No passenger baggage was carried on this aircraft, however examination of the baggage salvaged from the wreckage of 9M-ATZ revealed that some of it belonged to passengers on Nomad 9M-A0A.
After the passengers hoarded 914-ATZ, the engines were started and the aircraft taxied for departure at about 1504 hours. The take-off appeared normal and the aircraft reported its departure to Labuan Tower at 1509 hours. During the flight to Kota Kinabalu, the aircraft cruised at an altitude of 5,000 feet and appropriate en-route position reports were made to air traffic control.
When the aircraft was some six miles from Kota Kinabalu and the .pilot had reported visual flight conditions, it was cleared by air traffic control to descend to 3,000 feet and join a right-hand downwind circuit leg, to land on Runway 20.
This clearance was acknowledged by the aircraft commander.
The aircraft descended to 3000 feet on the downwind leg and was cleared for further descent end instructed to report passing 2000 feet. This instruction was also acknowledged by the aircraft commander.
During its approach, 9M-ATZ was the second aircraft in a traffic sequence of three aircraft all landing on Runway 20.
The first aircraft, a Cessna 421, landed whilst 9M-ATZ was on downwind leg and the third aircraft, a Boeing 737, was being processed by air traffic control and progressively descended to follow 9M-ATZ in the landing sequence.
914-ATZ reported high downwind and was cleared to final approach. Shortly thereafter, the preceeding aircraft having landed, 9M-ATZ WAS informed that it was number one in traffic and was again requested to report passing 2000 feet. The acknowledgement of this instruction was the last transmission received from the aircraft.
The tower controller observed 9i-ATZ carry out an apparently normal base leg and turn onto final approach. When the aircraft was lined-up on final approach, the tower controller transmitted “Tango Zulu cleared to land; wind is 280 degrees 5 knots”.
The aircraft did not acknowledge this transmission and it was repeated by the tower controller some seven seconds later. Again there was no acknowledgement from the aircraft.
Almost immediately, the controller observed the right wing of the aircraft dip momentarily and then rise to a level position after which the aircraft entered a spin to the right during which height was lost. Eye-witness evidence indicates that after one turn of the spin, the aircraft: recovered momentarily in a nose down attitude but almost immediately the spin to the right re-commenced and the aircraft struck the sea-bed after passing through some two feet of water in a steep nose down attitude.
1.2. Injuries to persons
Injuries Crew Passengers Others
Fatal 1 10 0
Non-fatal 0 0 0
Others 0 0 0
1.3. Damage to Aircraft
The aircraft was completely destroyed by impact forces and the results of immersion in salt water.
1.4. Other Damage. There was no other damage.
1.5. Crew Information
Pilots: Aged: 42 years
Licences: Commercial Pilot Licence (CPL) valid until 30 Nov. ‘76
R/T Licence: Restricted
Aircraft Ratings: PA28-140/180, PA23 Aztec. PA34-200, N22B Nomad
Instrument Rating: Valid until 21 Aug. ‘76
Medical Certificates: Valid until 3 Nov. ‘76
Last Competency Checks: Initial Flying Conversion to Nomad N22B: 18 Oct. ‘75
Flying Experience Approximately total flying hours: 3062 hours
Approximately flying hours on type: 129 hours
The pilot’s original flying log book was claimed to have been burnt in June 1969 and the replacement flying log book was claimed to have been stolen in November, 1975. The transfer of the total hours from the two previous flying log books cannot be authenticated, nor is it verified by the Company.
The monthly summaries since the new log book was opened until the last entry on 12th April, 1976 was also never checked or verified by the Company. The total flying hours are only an approximation based on the available information in the pilot’s new log book and from the Company’s flight authorisation book.
As far as can be established from records available the pilot has a history of poor performances in flying. His training record and performance whilst with the Company has also been marginal.
The pilot first joined the Sabah Flying Club on 1st April, 1974. Penerbangan Sabah was then incorporated with the Sabah Flying Club and later became a statutory body coming under the jurisdiction of the Sabah Economic Development Corporation (SEDC). The pilot elected to join Penerbangan Sabah when it was transferred to SEDC on let November, 1974.
1.6. Aircraft Information
The GAF Nomad N228 is a multi-purpose twin engined high wing monoplane. The wing is strut braced and retractable undercarriage is fitted. Each General Motors Allison 250-11170 free turbine engine drives a three bladed Hartzell controllable pitch metal propeller. Full dual controls and a Collins three axis auto-pilot were fitted.
At the time of the accident the aircraft was fitted with eleven seats, including two side by side pilot spate and four VIP seats. In the cabin the first two V.I.P. seats faced the rear and the remainder of the seats were forward facing. Standard forward and aft baggage compartments were available in the aircraft.
Manufacturer: Government Aircraft Factories Australia.
Date of Manufacture: 1975
Certificate of Registration: The aircraft was registered in the name of Penerbangan Sabah on 19th November, ‘75.
Certificate of Airworthiness: Category: Normal
Sub-Divisions: a, b, c, d, e, f & i. (This therefore includes Transport Passenger Category) and valid until 18th November, 1976.
The aircraft had been maintained in accordance with approved maintenance schedule PS/N228 Issue 1 dated 12th September ‘75.
Total time since built: 229 hours 21 mins. (The last flight is estimated as 25 min)
Time since last check: 47 hours 19 mins.
Total engine time: 229 hours 21 mins, (left)
229 hours 21 mins. (right)
Time since last inspection: 47 hours 19 mins. (left), 47 hours 19 mins. (right)
Aircraft Loading
Empty weight data for the aircraft was derived from the manufacturers original weighing report (CA 65). Examination of the wreckage showed that the original cabin configuration had been altered by the removal of the toilet and screens and the installation of standard Nomad rear seats.
No other changes were made and an accurate empty weight could be established by calculation.
Some seats were not located in the usual positions but the actual positions could be obtained from the seat remains on the seat rails and by reference to the location stations stamped upon the rails. Seat weight data was available from manufacturer’s reports.
Prior to the departure from Labuan on the accident flight the aircraft had 000 lb. of fuel.
The baggage recovered from the aircraft was weighed end allowance for water content established to determine the calculated dry weight of the baggage. The baggage recovered from the forward baggage compartment amounted to 177 lbs. This baggage was trapped in the remains of the aircraft nose. The maximum load permitted in the forward baggage compartment is 400 lbs. It. is estimated that a load of 325 lbs. was placed in the aft baggage compartment and a further 90 lbs. of personal effects Was distributed throughout the cabin near the occupants. The maximum permissible load in the aft baggage compartment is 198 lbs.
The calculated take off weight was 8065 lbs. This was below the maximum take off weight of 0500 lbs. but the Centre of Gravity was at 43.61% mean aerodynamic chord (MAC). This is outside the prescribe roar limit of 38.5% MAC.
During the flight to Kota Kinabalu, it is calculated that 200 lbs, of fuel was burnt off leaving 600 lbs, of fuel. The Centra of Gravity moved from 43.61% to 43.76% MAC and the weight reduced to 7855 lbs. at the time of the accident.
The basis for the above figures con be seen in Appendix A.
1.7 Meteorological Information
On the short sector (61 miles) between Kota Kinabalu and Labuan, rout forecasts ace not provided as the pilot has access to actual aerodrome weather observations by radio from the air traffic control facilities located at the two aerodromes.
Meteorological observations are made at Kota Kinabalu Aerodrome at half-hourly intervals, on the hour and the half-hour. The weather observation made at 1530 hours on 6th June, 1976, some 12 minutes prior to the accident was:
slight rain, wind 270 degrees 3 knots
visibility 30 kilometres
2/8 cloud based at 1500 feet
3/8 cloud based at 2000 feet
6/8 cloud based at 18000 feet
OH altimeter setting 1008 millibars
temperature 28 degrees Celsius
The weather observation made at 1600 hours on 6th June, 1976 some 18 minutes after the accident was:
fine, wind calm
visibility 30 kilometres
2/8 cloud based at 1500 feet
5/8 cloud based at 28000 feet
OH altimeter setting 1008 millibars
temperature 28 degrees Celsius,
There was no evidence that the weather conditions contributed in any way to the accident.
1.8 Aids to Navigation
The flight was conducted under the visual flight rules and the availability or serviceability of radio navigation aids was not a factor in the accident.
1.9 Communications
Communications between the aircraft and the Control Towers at Labuan and Kota Kinabalu were recorded on continuously running magnetic tape. Relevant parts of the transcript have been Included in para 1.1. History of the flight.
1.10 Aerodrome and Ground Facilities
The aerodrome at Kota Kinabalu has a single sealed runway aligned 021/201 degrees magnetic and 9800 feet in length. The aerodrome is equipped with high intensity runway lights and there is a VASIS on Runway 02. There are no approach aids for landing on Runway 20.
1.11 Flight: Recorder
There is no requirement for this aircraft to be equipped with a flight recorder and none was fitted.
1.12 Wreckage
The aircraft struck the ground/water with considerable force in a near vertical sense.
There was no evidence of forward speed relative to the ground and It was clear that the aircraft struck at an angle of at least 60° to the horizontal.
Damage to both mainplanes and engines confirmed that the aircraft was not turning at impact.
The wreckage occupied an area of about 40 ft. by 40 ft. in shallow water. It was on the centre line of runway 20 some 5676 ft. short of the threshold and 177 ft. out from the jetty or cat walk which runs parallel to Jalan Pantai Sembulan. The wreckage was facing away from the approach to runway 20 on a heading of approximately 020
Due to the rescue work which took place before the Investigating Team arrived some evidence was lost due to considerable damage which was inflicted on the wreckage during the process of moving and separating major components.
The angle of impact was such as to cause the fuselage, aft of stn 292, to fail on the lover side. This allowed the rear portion of the fuselage to rotate up and over the front fuselage with the top of the fin and rudder coming to rest in the cockpit area. The mainplanes had both moved forward at impact, following the failure of the wing struts at their inboard ends. The cockpit area was badly crushed on impact.
The structure forward of the stub wings was foreshortened to about two feet, as a result the cockpit area was very badly compressed. The centre fuselage frames and structure were essentially intact and the damage sustained was consistent with the impact. The main cabin floor was still in one place and it was noted that the seat attachments were in place. Seat structures failed as a result of the impact and rescue work. The rear fuselage, tailplane and fin was complete and relatively undamaged apart from the top of the fin and rudder. The top of the fin above will 198 was crushed in the leading edge area by about one foot.
The fin main spar failed due to compression buckling about one foot above the base of the fin. There was no evidence of pre-crash failure in the structure or tailplane.
The mainplanes which were still attached were found to have been moved upwards relative to the fuselage by about 40 each during the rescue. It was evident that the Impact had caused both mainplanes, outboard of str. 144 to be crushed in the leading edge area.
This resulted in the mainplanes suffering increasing crushing damage towards the tip such that the tip chord had been reduced by about 50%.
The stub wing structure and wing struts were only damaged as a result of the impact.
The fuel system was checked and found satisfactory; fuel LP filters indicated some contamination of the std. system and less in the port. The std. filter contamination was not sufficient to restrict flow to that engine.
The flying controls of the aileron/flaps, spoilers, tailplane and rudder were all examined in detail and apart from the rudder control torque shaft under the pilots pedals, which was missing, it was possible to trace all parts. Only one link in the inboard flap hinge port side displayed an unusual failure, this was therefore sent for export metallurgical examination. There is, however, a second link for the inboard port flap which would take the full load should the other link fail. Only the flap position could be established beyond doubt at a setting of 25c.
Though not conclusive, it is possible from witness marks on the fin, that the tailplane was set in a full UP position. The damage found throughout the flying control system was consistent with the impact forces when the aircraft struck the ground. There was no evidence of pre-crash failure. The tailplane trim position was established at 10D which is full down. This position can only be related to a very aft C of G position. The rudder trim position was contradictory in that the cockpit indication was AR yet the chain position on the rudder trim screw jack was virtually neutral.
The undercarriage was found to be down and locked with no indication of pre-crash failure. The autopilot fitted to this aircraft had been declared unserviceable and whilst It was not possible to establish whether it was selected on, there is no reason to suppose that it vas.
An examination of the engine control settings proved inconclusive due to contradictory settings on the same engine. It was evident that the impact forces had distorted the true settings of the controls. It was therefore decided to split both engines at the 4th stage turbine face. Examination of the third stage turbine nozzle and the 4th stage turbine indicated that both engines were operating above flit idle but well below maximum power. The most likely power setting was probably around 30 psi torque. It was also evident from the 3rd stage nozzle examination of both engines that the port was at a slightly higher power setting than the std. This evidence was contradicted by the propeller damage which indicated substantially the same power from both engines.
With the exception of the right engine torque indication and the stall warning audio there was no evidence to indicate pre-crash failure of the cockpit indications.
However, it was only possible to establish the following instrument and system control positions.
Pilots ASI: 86 kts
Pilots clock: 3 hours 41 mins. 27 secs.
Both altimeters: 1008 mb
Fuel select left: ON
Fuel select right: ON
Crossfeed: BOTH
The right engine torque indication failed at some stage because the fuse protecting the torque circuit had bloom. Examination of the various system components indicated that the fuse probably blew as a result of a wiring chort circuit on the back of the torque indicator at impact. The aural warning circuit breaker had tripped. Examination of the aural box mounted in the cockpit indicated that again impact damage was probably responsible for tripping the circuit breaker.
One of the effects of this circuit breaker when tripped would be to mute the stall warning system vanes mounted on the port mainplane leading edge.
In view of the Visual Flight Rule procedure being used at the time of the accident it is reasonable to assume that instruments had no bearing on this accident.
Communication equipment of the aircraft consisted of two VHF Nav/Comns, two ADP’s and one HF radio. It was noted that only the VHF equipment was selected ON. Therefore only the positions of the VHF selector have been included.
Radio NAV. 1 113.1 MHz (KK VOR IDENT VIN)
Rario COM. 1 119.1 MHz (KK APPROACH)
Radio NAV. 2 Between 112.15 MHz & 113.1 MHz
Radio COM. 2 119.1 Miz (KK APPROACH)
The communication equipment is considered to have no bearing on this accident and there is no reason to believe it suspect.
There was no evidence of explosion or any form of sabotage.
1.13 Medical and Pathological Information
Post Mortem examinations showed that all the occupants had died from extensive multiple injuries. There was no evidence that the plot was suffering the effect of alcohol or drugs apart from an anti-malarial called chloroquine.
1.14 Fire
There was no evidence of fire either in the air or after the subsequent impact with the water.
1.15 Survival Aspects
This was not a survivable accident.
1.16 Tests and Research
1.16.1 Flap link Examination
The report from Australia indicated that the link failed due to overloud in bending. There was no evident of pre-failure cracks and the material properties were typical of a 2024 alloy which had been heat treated to I851 temper standard.
1.16.2 Hundling report
The Government Aircraft Factory of Australia produced a report covering the handling properties of the Nomad. The data from this report has been used in compiling the graphs at the and of this report.
2. ANALYSIS & CONCLUSIONS
2.1 Analysis
There is no evidence to suggest any failure of the aircraft or its systems prior to the accident. The last maintenance was carried out on the preceding Friday when an attempt to rectify a recurring defect of “undercarriage fails to retract after take off proved inconclusive. This was due to the intermittent nature of the defect and in any caso would have no bearing on the events leading up to the end, because it would have been apparent during take-off from Labuan. The failed link in the port inboard flap inner hinge could not have affected the situation because the port inboard flap is connected in two places and the second link did not fail. The stall warning failure which has not been conclusively proved due to the impact could possibly, though unlikely, have been contributory too, but not the cause, as it is merely a warning of approach to the stall.
With engines under power at the time and no evidence of sabotage, explosion or fire it is clear that the aircraft was not the cause of the accident.
Pathological tests on the pilot proved that he was reasonably fit at the time and not suffering from the effects of alcohol or drugs; though there 1s other evidence to suggest he was tired and had a mild stomach disorder.
The aircraft was fitted with duplicate flying controls and a passenger is permitted to occupy the co-pilot’s seat in the absence of another qualified pilot. However, the pilot-in-command should brief any such occupant not to interfere or obstruct the flying of the aircraft. In investigating probable causes of the accident, an examination of the rudder pedals indicated that to sit comfortably on the seat which only has vertical adjustment, the fact can be placed under the pedals.
Very little clearance is left and any sharp backward movement of the pedals (eg. engine failure on take off) could over-ride the feet and possibly cause Jamming of the rudder pedals. It is however most unlikely that jamming of the pedals took place in this case.
The Daily Express’ award winning team of journalists presents ‘Double Six: The Untold Stories’, a documentary on the plane crash in Sabah (East Malaysia) killing the newly-elected Chief Minister of Sabah Tun Mohd Fuad Stephens, four state ministers and six others on June 6th, 1976. After 46 years the findings of the crash also known to many as The Double Six Tragedy have not been disclosed. Note: This series unravels information not previously available to the public, but does not in any way attribute blame for the crash on any party.
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