Sukhoi SU95 over Indonesia on May 9th 2012, aircraft impacted mountain

Last Update: December 18, 2012 / 12:53:34 GMT/Zulu time

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Incident Facts

Date of incident
May 9, 2012

Aircraft Registration

ICAO Type Designator

Indonesia's National Transportation Safety Committee (NTSC) released their final report concluding the probable causes of the crash were:

- The flight crew was not aware of the mountainous area in the vicinity of the flight path due to various factors such as available charts, insufficient briefing and statements of the potential customer that resulted in inappropriate response to the TAWS warning. The impact could have been avoided by appropriate action of the pilot up to 24 seconds after the first TAWS warning.

- The Jakarta Radar service had not established the minimum vectoring altitudes and the Jakarta Radar system was not equipped with functioning MSAW for the particular area around Mount Salak.

- Distraction of the flight crew from prolonged conversation not related to the progress of the flight, resulted in the pilot flying not constantly changing the aircraft heading while in orbit. Consequently, the aircraft unintentionally exited the orbit.

The captain (57, Test Pilot License first class, 10,347 hours total, 1,348 hours on type) was pilot flying for the demonstration flight RA-36801, the first officer (44, Test Pilot License second class, 3,318 hours total, 625 hours on type) was pilot monitoring. In addition a navigator (51, Test Navigator License first class, 3,533 hours total, 485 hours on type) and a test flight engineer were on board plus 41 passengers. The representative of a potential customer occupied the observer's seat in the cockpit.

The aircraft departed Halim Perdanakusuma Airport's runway 06, turned right to intercept radial 200 of HLM VOR (Halim Perdanakusuma Airport's VOR) and climbed to 10,000 feet. About 5 minutes after departure the crew reported level at 10,000 feet. Another 2 minutes later the crew requested to descend to 6,000 feet, the controller asked to repeat the request, the first officer repeated the request to descend to 6000 feet, to which the controller replied "6,000 copied". The first officer replied "Descending to 6,000 feet".

Further 2 minutes later the crew requested a right hand orbit, the controller approved the right hand orbit at 6,000 feet. At that point the aircraft was 17nm southwest of HLM VOR over the Atang Sanjaya Training Area.

22 minutes after the request for the right hand orbit the controller noticed the target had disappeared from his radar screen. Attempts to contact the aircraft over the next 3 minutes were without reply. The Air Traffic Services Operation Regional Coordinator subsequently attempted internal coordination to determine the position of the aircraft. 45 minutes after the aircraft target was detected missing INCERFA (Uncertainty Phase) was declared, after another 20 minutes ALERFA (Alert Phase) was declared and 3:32 hours after the target was detected missing DETRESFA (Distress Phase) was declared.

A helicopter pilot detected the location of the aircraft the following day about 17.5 hours after the aircraft target was detected missing. The aircraft had impacted a ridge of Mount Salak, facing to the east rising at an angle of 85 degrees, on radial 198 of HLM VOR 28nm from the VOR at 6000 feet at GPS coordinates S6.7125 E106.7347, the aircraft systems had recorded a last radio altitude of 370 feet.

The flight data and cockpit voice recorders ceased recording at 07:33:26Z, about 16.5 minutes prior to the air traffic controller noticing the target had been lost on his radar screen.

The recorders revealed that after departure from Jakarta the crew engaged LNAV mode which was active until during the descent to 6000 feet, too. At 07:27:24Z the commander commanded "heading", LNAV was disengaged and heading hold engaged. The aircraft was descending through 9200 feet at 211 KIAS at that time. At 07:28:21Z the right hand orbit was approved by air traffic control, the heading bug was moved to 333 degrees, then 033, 103 and 150 in sequence. The aircraft descended through 7700 feet at 210 KIAS.

The captain demonstrated the ability of the aircraft to fly holding patterns on the FMC, the first officer commented something could be seen through the clouds. At 07:29:27Z the captain announced the aircraft had levelled at 6000 feet, 47 seconds later the heading bug was set to 174 degrees.

The captain demonstrated the terrain awareness system to the observer by displaying the terrain on the navigation display and commented "but no problem with terrain, at this moment", the observer commented "ya, it's flat". Observer and crew engaged in a discussion about fuel consumption.

The captain instructed the first officer to request a right hand turn for the approach to Halim Airport, the first officer asked whether the commander intended another orbit or return to Halim, then repeated the question. In the meantime the autopilot began to roll out of the right hand turn and had wings level when the aircraft had reached the selected heading of 174 degrees at 07:31:53Z.

The first officer repeated his question again, the commander replied they'd make the approach. The first officer commented he would make the request after they had completed the orbit, the commander instructed to request the turn now, then hummingly tried to figure out the heading to Halim. The first officer suggested he could do that via the Legs Page on the FMC. The captain asked "Legs Page, which one?", the first officer was not able to find the heading information on the legs page and calculated the heading based on the outbound heading. The captain queried the calculation. At 07:32:24Z the captain stated the heading to Halim was 020 degrees and instructed at 07:32:29Z "on heading 020 for VOR/DME approach" and to request to descend to 1600 feet for the VOR/DME approach. The heading selector was moved to 325 degrees, the aircraft rolled into a right hand turn at 20 degrees of bank angle.

At 07:32:48Z the Terrain Awareness and Warning System (TAWS) alerted the crew "Terrain Ahead, Pull up!", 2 seconds later "Avoid Terrain!" and another second later "Avoid Terrain!" The first officer was puzzled "What is that?", the "Avoid Terrain!" alert sounded 4 more times, then the TAWS was selected inhibited. The captain commented "Maybe ... database".

At 07:33:19Z an aural alert "Gear not down" sounded, the side stick was moved resulting in the autopilot disconnecting simultaneously, the SYS and TERR buttons were pushed, the autopilot selected off, the chime indicating the autopilot off sounded. The first officer asked "What is that", the captain explained "Autopilot OFF" and the recordings ended.

Although the aircraft was equipped with an emergency location transmitter capable of transmitting on 406MHz, 121.5MHz and 243 MHz, no ELT signal was received from the crash site. The ELT was later recovered from the crash site with the antenna detached.

The NTSC conducted tests whether the TAWS alerts were in time to permit the aircraft climb to safety. The tests showed the TAWS did function as expected and provided correct information. Had the crew responded to the TAWS alerts timely, collision with terrain would have been averted, even if the crew had reacted only 24 seconds after the first TAWS alert only.

The NTSC analysed that on the outbound leg just prior to entering the orbit the first officer had commented on a dark cloud ahead, which indicated Mount Salak was in cloud. Further comment that the ground could be seen through the cloud further confirmed that the area at the training base was partially cloudy, too. While in the orbit, at approximately heading 070, the captain demonstrated the TAWS, at that time the terrain ahead of the aircraft was entirely flat. The NTSC analysed that the observer's comment "it's all flat" could have misled the crew to believe the entire terrain around their position was flat.

When the aircraft rolled out at heading of 174 degrees the crew inadvertently left the right hand orbit without completing the orbit that would have ended at 200 degrees. The NTSC analysed that the crew probably did not notice they had left the orbit and still believed they were turning evident by the first officer's remark he would request the return to Halim after the aircraft had completed the orbit.

During the following discussion about the return heading to Halim the aircraft travelled 4nm on heading 174 degrees, the captain was unaware of the mountaineous terrain around evident by his request to descent to 1600 feet for the approach to Halim.

Following the discussion the heaidng selector was rotated to 325 degrees and the aircraft began to turn right again. As soon as the aircraft rolled into the turn, the predictive function of TAWS, computing the turn performance as well, detected a conflict with terrain within 120 seconds and began to issue the related alerts. Following the TAWS inhibit not only the aural alerts, but visual alerts and terrain display were removed from the navigation display, too.

After the captain commented the alerts could be related to database, there was no communication between the pilots for 20 seconds until the gear not down warning and the simultaneous stick input occurred. The captain provided stick inputs to raise the nose to 5 degrees of pitch, the autopilot disconnected evident by the autopilot disconnected trickle sound.

The NTSC analysed that the captain's input to raise the nose to 5 degrees can not be seen as an escape maneouver. This would require to accelerate the engines to TOGA and flight control up input. The reason for the captain's input could not be determined by the investigation.

The NTSC concluded that simulator tests verified an escape maneouver could have avoided terrain contact until 24 seconds after the first TAWS alert, thereafter terrain contact could no longer be avoided.

The NTSC analysed that the briefing of the flight was incomplete and inadequate leaving the crew without information about the mountaineous area around Mount Salak.

The NTSC analysed that the controller had not understood the aircraft was a civil aircraft. When he looked up the type, he understood it was a Sukhoi military aircraft performing a test flight in the Bogor area and therefore was not concerned with the limits at the training area.

The NTSC analysed that the controller was under high work load with communication going on with the 13 aircraft in his area nearly continuously without pauses. The NTSC believes this is one of the factors why the aircraft was not detected missing from the radar screen. In a post occurrence interview the controller provided testimony that he felt over-loaded.

Following the mutliple TAWS alerts the captain disengaged the TAWS believing the alerts were the result of a database error.
Incident Facts

Date of incident
May 9, 2012

Aircraft Registration

ICAO Type Designator

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