Trigana AT42 enroute on Aug 16th 2015, aircraft collided with terrain
Last Update: December 29, 2017 / 16:13:27 GMT/Zulu time
Incident Facts
Date of incident
Aug 16, 2015
Classification
Accident
Airline
Trigana Air Service
Aircraft Registration
PK-YRN
Aircraft Type
ATR ATR-42
ICAO Type Designator
AT42
The deviation from the visual approach guidance in visual flight rules without considering the weather and terrain condition, with no or limited visual reference to the terrain resulted in the aircraft flew to terrain.
The absence of EGPWS warning to alert the crew of the immediate hazardous situation led to the crew did not aware of the situation.
The NTSC reported that the FDR could not be read out by the BEA, too, the FDR had repeated problems since 2013, had been returned to a repair facility several times. The NTSC wrote: "Since 2013 until the occurrence date showed that the FDR had several problems. The operator stated that the FDR unit was sent to the same repair station. The cause of the problem could not be detected. The investigation could not find any evidence of any maintenance action related to the aircraft system, which normally be taken if the recording problem on the FDR was caused by aircraft system problem."
The NTSC analysed:
The decision to descend below the safe altitude, outside any published IFR route, without or with only limited visual reference and in the high terrain area was the key issue leading to the accident. The investigation could not determine the reasons supporting this crew decision. Two kinds of explanation could be considered:
1- The previous experience of a success landing by flying direct to left base runway 11 might have triggered the flight crew to perform similar approach. However, the weather condition could have been different and might not have been fully considered by the flight crew. Since not all available information was considered, this might have resulted in lack of Situational Awareness which requires understanding of a great deal of information related to the goal of safely flying the aircraft.
The crew lack of situation awareness, while not being able to see the mountains that were covered by the clouds. However, it can be reasonably assumed that the crew was aware of the aircraft entering into the clouds, at least momentarily, despite the presence of significant terrain close to an airport they were familiar with. Their success in flying direct to the left base on the previous approach could let them think that this could be done again. According to the witness statement, most of the time the PIC did not follow the visual approach guidance while conducting approach at Oksibil. Although no other data was collected during the investigation to fully support the following hypothesis, it may not be excluded that a similar trajectory had already been performed in the past by this crew or by other crews, leading them to progressively take for granted the success of crossing the clouds and progressively lose awareness of the risks induced.
2- The crew had memorized the Minimum Safety Altitude published on the visual approach chart of 7,200 and 8,000 feet in the north-west sectors of the airport (see visual approach guidance chart in chapter 1.8 of this report) and intended to descent to 8,000 feet which was safe altitude according to the chart, hoping they could get sufficient visual reference to further descent in the final leg in the valley. The wreckage was found at elevation approximately 8,300 feet, higher than the 8,000 feet MSA published, which they may have believed they were safe.
With respect to the non-issuance of EGPWS cautions and warnings the NTSC analysed:
The Oksibil Airport was not provided with the high-resolution terrain data in this database version installed on the accident aircraft.
The operator’s management stated that some pilots within the air operator had experiences that the EGPWS warning became active in a condition that according to the pilots, the warning is not appropriate. These experiences led to the pilot behaviour of pulling the EGPWS circuit breaker to eliminate nuisance of EGPWS warning that considered unnecessary.
The air operator SOP stated that the warning may be regarded as a caution and the approach may be continued when flying under daylight VMC conditions, a warning threshold may be deliberately exceeded due to a good knowledge of the present terrain. A go-around shall be initiated if the cause of the warning cannot be identified immediately.
The management had identified some pilots including the accident pilot of the pilot with behaviour of pulling EGPWS CB. The management had scheduled a briefing to the accident pilot related to this behaviour and other issues.
The investigation concludes that, most probably, the EGPWS power supply circuit breaker was pulled during the accident flight and the two previous flights, explaining the absence of altitude call out during the two previous approaches and warning prior to the impact.
The NTSC analysed with respect to oversight over the organisation:
The investigation identified several safety issues existed prior to the occurrence. The aircraft operator issued visual approach guidance chart to provide guidance for flight crew since there was no approach guidance published by authority in Oksibil.
The visual approach guidance chart stated that the minimum safe altitude was 8,000 feet while the aircraft impacted with terrain at approximately 8,300 feet. This indicated an incorrect information in the chart. The investigation considered that the pattern on the approach guidance chart was not easy to fly, as many altitudes and heading changes.
The CVR revealed that the flight crew deviated from the visual approach guidance while conducting the approach to Oksibil on the previous flight. The witness also stated that the pilot deviated from the visual approach guidance at most of the flight to Oksibil.. The deviation from the visual approach guidance was not identified by the aircraft operator.
The CVR did not record any crew briefing and checklist reading from cruising up to the impact. The aircraft operator COM required certain items to be briefed for flight and checklist should be performed minimum of two times during descend and approach, which consisted of descend checklist and approach checklist. The flight crew behaviour of performing flight without briefing and checklist reading did not identify by the aircraft operator. The investigation could not establish whether it was specific to this crew or frequent within the air operator.
The aircraft operator identified that several pilots including the accident pilot had behavior of pulling the EGPWS CB. However, correction to this behavior was not performed in a timely manner.
The investigation found that several maintenance records such as component status installed on the aircraft and installation of EGPWS was not well documented. This indicated that the maintenance management was not well performed.
These safety issues indicated that the organization oversight of the aircraft operator was not well implemented.
Incident Facts
Date of incident
Aug 16, 2015
Classification
Accident
Airline
Trigana Air Service
Aircraft Registration
PK-YRN
Aircraft Type
ATR ATR-42
ICAO Type Designator
AT42
This article is published under license from Avherald.com. © of text by Avherald.com.
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