Scheduled Revenue Flight

The separation of the flexible fuel line coupling and subsequent fuel leak due to the failure of maintenance personnel to install the required safety lockwire. Contributing to the severity of the accident was the initiation of the evacuation before the right engine was shut down which led to the passenger's injury.

Unstable approach whereby the aircraft was flared too high with high forward speed resulting with a low sink rate in which during touch down the left landing gear
experienced excessive vibration and failed due to shimmy events.
The following findings were identified:
- According to the FDR recordings, the aircraft flare was initiated earlier at 65ft than at 20ft as recommended by aircraft manufacture, which contributed to the low sink rate.
- The shimmy damper failed the post-accident lab-test and fluid was found in the thermal relief valve, which could have contributed to the shimmy damper failure.
- According to the lab results, significant wear was found on the upper torsion link bushing and flange, which could have contributed to undamped vibration
continuation.
- The aircraft had a tailwind component during landing, which could have prolonged the landing distance.

Unstable approach and inadequate landing technique for high altitude fields, which resulted in increased landing speed, the start of the flare manoeuvre at higher altitude, and low descent speed, which made the OB-2040-P aircraft make soft contact with the runway, causing inefficiency in operation of the shimmy damper, which did not prevent uncontrolled oscillation of the shock absorbers.
Contributing factors:
- Lack of instruction and training in simulators that include techniques and maneuvers of landing at high altitude fields, with emphasis on speed control at landing.
- Lack of a performance analysis process, through the use of flight recorders or other installed data recording equipment and flight parameters, by the operating company, to enable supervision, control and corrective measures in the operational use of its aircraft.

The following findings were identified:
1. The aircraft had valid Certificate of Airworthiness prior to the accident and was operated within the weight and balance envelope.
2. Both pilots had valid licenses and medical certificates.
3. The accident flight from Masamba (WAFM) to Makassar (WAAA) was the 6th sector for the aircraft and the crew that day. The PIC acted as Pilot Flying and the
SIC acted as Pilot Monitoring.
4. The satellite image published by BMKG at 0700 UTC showed that there were cloud formations at the accident area. The local villagers stated that the weather
on the accident area was cloudy at the time of the accident.
5. The aircraft departed Masamba at 0625 UTC (1425 LT), conducted under VFR with cruising altitude of 8,000 feet and estimated time of arrival Makassar at 0739 UTC.
6. After reached cruising altitude, at about 22 Nm from Masamba, the flight deviated from the operator visual route and directed to BARRU on heading 200° toward the area with high terrain and cloud formation based on the BMKG satellite image
7. The pilots decision making process did not show any evidence that they were concerned to the environment conditions ahead which had more risks and required correct flight judgment.
8. The CVR did not record EGPWS aural caution and warning prior to the impact. The investigation could not determine the reason of the absence of the EGPWS.
9. The CVR data and cut on the trees indicated that the aircraft was on straight and level flight and there was no indication of avoid action by climb or turn.
10. The SAR Agency did not receive any crashed signal from the aircraft ELT most likely due to the ELT antenna detached during the impact.
11. Regarding to the operation of the EGPWS for the flight crew, a special briefing was performed however there was no special training.
12. The operational test of TAWS system was not included in the pilot checklist.
13. The investigation could not determine the installation and the last revision of TAWS terrain database.
14. The investigation could not find the functional test result document after the installation of the TAWS.
15. Some of the DHC-6 pilots have not been briefed for the operation of the TAWS and EGPWS.

Contributing Factors:
Deviation from the company visual route without properly considering the elevated risks of cruising altitude lower than the highest terrain and instrument meteorological condition in addition with the absence of the EGPWS warning resulted in the omission of avoidance actions.

The air accident was the result of an early retraction of the retractable landing gear during take-off, which was not prevented by the landing gear selector lever and the retracting control logic.
Contributory factors:
- Reduced concentration level,
- A break in the callout process / task sequence on the part of the PNF,
- Actuation of the landing gear lever to the UP Position too early,
- Control logic design allows retraction of the landing gear with one wheel airborne.

Findings as to causes and contributing factors:
1. Delivery of the incorrect type of aircraft fuel caused loss of power from both engines, necessitating a forced landing.
2. The fueling operation was not adequately supervised by the flight crew.
3. A reduced-diameter spout was installed that enabled the delivery of Jet-A1 fuel into the AVGAS fuel filler openings.
4. The fuel slip indicating that Jet-A1 fuel had been delivered was not available for scrutiny by the crew.

Findings as to risk:
1. If administrative and physical defences against errors in aviation fuel operations are circumvented or disabled, there is a risk that the incorrect type of fuel will be delivered.
2. If a reduced-diameter spout is available to accommodate non-standard fuel filler openings, there is an increased risk that Jet-A1 fuel can be dispensed into an aircraft that requires AVGAS.

Other findings:
1. Aircraft that were manufactured prior to the current airworthiness standards, or that have been modified by the installation of turbine engines, may have fuel filler openings that do not meet the dimension requirements.
2. The airworthiness standards for rotorcraft do not specify the size of fuel filler openings.
3. The use of all of the available restraint systems in the aircraft contributed to the survival of the occupants.
4. There was no post-crash fire, likely due to the separation of the battery from the aircraft and to the rain-saturated crash site.
5. The absence of a post-impact fire contributed to the survival of all of the aircraft's occupants.

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.