Special Region of Papua

The possibility of the pilot being fatigue, physical and environment condition increased pilot sleepiness which might have made the pilot inadvertently falling asleep indicated by no pilot activity. The absence of GA-EGPWS aural alert and warning was unable to wake up the pilot.

Refer to the previous aircraft that was landed safely, the pilot confidence that a safe landing could be made and disregarding several conditions required for go around.

According to factual information during the investigation, the Komite Nasional Keselamatan Transportasi determines the findings of the investigation are listed as follows:
1. The pilots held valid licenses and medical certificates.
2. The aircraft had a valid Certificate of Airworthiness (C of A) and Certificate of Registration (C of R), and was operated within the weight and balance envelope.
3. There were no reports of aircraft system abnormalities during the flight.
4. After passed JIWIKA on altitude 10,000 feet, the FDR recorded the engines were on idle, the average rate of descend was approximately 2,000 feet per minute.
5. At altitude approximately 8,000 feet, the flap selected to 40 position and moved to 39.9° one minute 25 seconds later.
6. The BMKG weather report was wind 150°/14-19 knots and the Wamena Tower controller reported to the pilot that the wind was 150°/15 knots. The information of gust wind, which indicated the possibility of windshear, was not reported to the pilot.
7. The EGPWS “CAUTION WINDSHEAR” active on altitude of 5,520 feet.
8. 06:45:43 UTC, the engine power increased when the aircraft altitude was on 5,920 feet prior the EGPWS altitude call “ONE HUNDRED” heard.
9. Started from 06:45:45 UTC, the FDR recorded the CAS increased from 148 knots to 154 knots followed by N1 decreased gradually from 73% to 38%. Three seconds before touched down, the rate of descend was constant on value 1,320 feet per minute followed by EGPWS warning “SINK RATE”.
10. The aircraft touched down at about 35 meters before the beginning runway 15 with the vertical acceleration recorded of 3.68 G.
11. The trunnion link of the left Main Landing Gear (MLG) assembly was found broken and the left main landing gear collapsed.
12. The FDR data contained of 107 flight hours consisted of 170 flight sectors which recorded five times of the vertical acceleration more than 2 G during landing at Wamena. The accumulation of such value of vertical acceleration might lead to landing gear strength degradation.
13. The Visual Approach Slope Indicator (VASI) of runway 15 was not operated after the runway extension.
14. The investigation found several touchdown marks on the pavement before the runway 15.
15. Excessive rubber deposit was found on the surface of runway 15 at about 600 meter started from the runway threshold.
16. The absence of speed correction following the information of headwind of 15 knots and pilot crew briefing after activation of EGPWS caution windshear indicated that the pilot did not aware of the existing windshear, that might be contributed by the absence of gust wind information.
17. The large thrust reduction was not in accordance with the FCOM for windshear precaution and resulted in rapid descend.
18. The accident flight collapsed the landing gear, the FDR recorded the vertical acceleration was 3.683 G which was within the landing gear design limit. This indicated the degradation of landing gear strength.

Contributing Factor:
The large thrust reduction during the windshear resulted in rapid descend and the aircraft touched down with 3.683 G then collapsed the landing gear that had strength degradation.

The following findings were identified:
1. The aircraft had valid Certificate of Airworthiness and was operated within the weight and balance envelope.
2. All crew had valid licenses and medical certificates.
3. The flight plan form was filed with intention to fly under Instrument Flight Rule (IFR), at flight level 155, with route from Sentani to MELAM via airways W66 then to Oksibil. The MORA of W66 between Sentani to MELAM was 18,500 feet.
4. The flight was the 5th flight of the day for the crew with the same aircraft and the second flight on the same route of Sentani to Oksibil.
5. The CVR data revealed that the previous flight from Sentani to Oksibil the flight cruised at altitude of 11,500 feet and the approach was conducted by direct to left base runway 11.
6. The CVR data also revealed that on the accident flight, the flight cruised at altitude 11,500 feet and intended to direct left base leg runway 11 which was deviate from the operator visual guidance approach that described the procedure to fly overhead the airport prior to approach to runway 11.
7. The witness stated that most of the time, the flight crew deviated from the operator visual approach guidance. The deviation did not identify by the aircraft operator.
8. The downloading process to retrieve data from the FDR was unsuccessful due to the damage of the FDR unit that most likely did not record data during the accident flight. The repetition problems of the FDR unit showed that the aircraft operator surveillance to the repair station was not effective.
9. The CVR did not record any crew briefing, checklist reading and EGPWS altitude callout prior to land on two previous flights nor the EGPWS caution and warning prior to impact.
10. The spectrum analysis of the CVR determined that both engines were operating prior to the impact.
11. Several pilots, had behavior of pulling the EGPWS CB to eliminate the nuisance of EGPWS warning. The pilots stated that the reason for pulling the EGPWS CB was due to the pilots considered this warning activation was not appropriate for the flight conditions. The correction to this behavior was not performed prior to the accident.
12. The investigation could not determine the actual EGPWS CB position during the accident flight.
13. The installation of EGPWS by the aircraft operator was not conducted according to the Service Bulletin issued by the aircraft manufacturer.
14. The terrain data base installed in the EGPWS of PK-YRN was the version MK_VIII_Worldwide_Ver_471 that was released in 2014. The Oksibil Airport was not included in the high-resolution update in this version of terrain database.
15. The information for Oksibil published in AIP volume IV (Aerodrome for Light Aircraft/ALA) did not include approach guidance. The operator issued visual guidance of circling approach runway 11 for internal use.
16. 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.
17. 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.
18. The investigation could not find any regulation that describes the pilot training requirement for any addition or modification of aircraft system which affect to the aircraft operation.
19. There was no information related to the status of ZX NDB published on NOTAM prior to the accident.
20. Several safety issues indicated that the organization oversight of the aircraft operator by the regulator was not well implemented.
Contributing Factors:
1. 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.
2. 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 following findings were identified:
1. Continuing the flight with both airspeed indicators unserviceable increased the complexity of the flight combined with high-risk aerodrome increased the pilot workload.
2. The improper corrective action at the time of the aural stall warning activating on the final approach, and the aircraft flew to insufficient area for a safe maneuver.
3. The unfamiliarity to the airstrip resulted in inappropriate subsequent escape maneuver and resulted in the aircraft stalling.
4. The pilot was not provided with appropriate training and familiarization to fly into a high-risk airstrip

Contributing Factors:
- The failure to airborne was due to the aircraft was not in correct takeoff configuration which required wing flap 20° while the flap was found at approximately 6° position during impact.
- The actions to recover the situation by selection of emergency power and flap were not proper for particular condition.

The following contributing factors were identified:
- The flight did not meet the criteria according to the recommended elements of stabilized approach which required go around.
- The aircraft touched down with 2° misalignment with the runway direction then the aircraft veered off to the left.
- The recovery action was not in accordance to the correct technique according to the ALAR Tool Kit.