Cargo

The accident was the consequence of the combination of the following factors:
a) Failure to initiate a rejected take off during take off roll following the indication of engine failure;
b) Failure to adhere to the company SOP following the detection of the engine failure during take off;
c) Considering the poor visibility at Cox’s Bazar Airport, diverting to the alternate airfield Chittagong Airport located only 50 nm away that has the provision for full ILS approach facility. This could have helped the crew in carrying out a proper one engine out precision approach landing;
d) The aircraft flew at a speed much lower than the clean configuration speed. The aircraft flew at 225 km/h in clean configuration whereas the minimum clean configuration speed is 290 km/hr.
e) As per the FDR data the aircraft stalled while making a turn towards the side of the failed engine at a very low altitude.

The erroneous attitude indication on PFD 1 was caused by a malfunction of the Inertial Reference Unit (IRU 1). The pitch and roll comparator indications of the PFDs were removed when the attitude indicators displayed unusual attitudes. In the simulator, in which the crew had trained, the corresponding indications were not removed. During the event the pilots initially became communicatively isolated from each other. The current flight operational system lacked essential elements which are necessary. In this occurrence a system for efficient communication was not in place. SHK considers that a general system of initial standard calls for the handling of abnormal and emergency procedures and also for unusual and unexpected situations should be incorporated in commercial aviation. The accident was caused by insufficient operational prerequisites for the management of a failure in a redundant system.
Contributing factors were:
- The absence of an effective system for communication in abnormal and emergency situations,
- The flight instrument system provided insufficient guidance about malfunctions that occurred,
- The initial maneuver that resulted in negative G-loads probably affected the pilots' ability to manage the situation in a rational manner.

Findings as to causes and contributing factors:
1. Although the aircraft was prohibited from flying in known or forecast icing conditions, Wasaya Airways Limited Partnership (Wasaya) flight 127 (WSG127) was dispatched into forecast icing conditions.
2. The high take-off weight of WSG127 increased the severity of degraded performance when the flight encountered icing conditions.
3. The pilot of WSG127 continued the flight in icing conditions for about 6 minutes, resulting in progressively degraded performance.
4. WSG127 experienced substantially degraded aircraft performance as a result of ice accumulation, resulting in aerodynamic stall, loss of control, and collision with terrain.
5. The Type C pilot self-dispatch procedures and practices in use at Wasaya at the time of the occurrence did not ensure that operational risk was managed to an acceptable level.
6. Wasaya had not implemented all of the mitigation strategies from its January 2015 risk assessment of Cessna 208B operations in known or forecast icing conditions, and the company remained exposed to some unmitigated hazards that had been identified in the risk assessment.
7. There was a company norm of dispatching Cessna 208B flights into forecast icing conditions, although 4 of Wasaya’s 5 Cessna 208B aircraft were prohibited from operating in these conditions.

Findings as to risk:
1. Without effective risk-management processes, aircraft may continue to be dispatched into forecast or known icing conditions that exceed the operating capabilities of the aircraft, increasing the risk of degraded aircraft performance or loss of control.
2. If pilots operating under self-dispatch do not have adequate tools to complete an operational risk assessment before releasing a flight, there is an increased likelihood that hazards will not be identified or adequately mitigated.
3. If aircraft that are not certified for flight in known or forecast icing conditions are dispatched into, and encounter, such conditions, there is an increased risk of degraded performance or loss of control.
4. If aircraft that are certified for flight in known or forecast icing conditions are dispatched into, and encounter, such conditions, at weights exceeding limitations, there is an increased risk of loss of control.
5. If flights are continued in known icing conditions in aircraft that are not certified to do so, there is an increased risk of degraded aircraft performance and loss of control.
6. If operators exceed aircraft manufacturers’ recommended ICEX II servicing intervals, there is an increased risk of degraded aircraft performance or loss of control resulting from greater accretion of ice on the leading-edge de-icing and propeller blade anti-icing boots.
7. If pilots do not receive the minimum required training, there is an increased risk that they will lack the necessary technical knowledge to operate aircraft safely.
8. If pilots are not provided with the information they need to calculate the aircraft’s centre of gravity accurately, they risk departing with their aircraft’s centre of gravity outside the limits, which can lead to loss of control.
9. If emergency locator transmitter antennas and cable connections are not robust enough to survive impact forces, potentially life-saving search-and-rescue operations may be impaired by the absence of a usable signal.

Other findings:
1. Wasaya’s use of a satellite aircraft flight-following system provided early warning of WSG127’s abnormal status and an accurate last known position for search-and-rescue operations.
2. The investigation could not determine whether the autopilot had been used by the pilot of WSG127 at any time during the flight.

When the controller received the estimated time of arrival for TSY810 from the Flight Information Center (FIC) Nairobi he advised FIC Nairobi (Kenya) that Mogadishu Airport was closed at the estimated time of arrival and advised the crew should divert to their alternate aerodrome but received no feedback. At 14:45Z the tower received first communication from the crew advising they would be overhead the aerodrome at 15:02Z, the controller advised again that the aerodrome would already be closed by then, the crew insisted however that they would land. Tower provided the necessary landing information like weather and active runway. At 15:02Z there was no sight of the aircraft, tower queried with the crew who reported still being 54nm out and revised their estimated time of arrival. At 15:27Z the aircraft turned final for runway 05, tower advised the crew to land at own discretion as tower's "instructions were only advisory and not clearance". The controller added that the approach was aborted and all subsequent approaches were unsuccessful too. "At one point the pilot mistook street parallel to the runway lighted by flood lights with intention of landing but was alerted the runway was on his right and the approach was discontinued. The crew has been warned numerous times that Mogadishu Airport closed at 1800LT (1500Z) and there is no adequate runway lights as the airport is not prepared to receive flights during night time hours. Thus, the pilot has intentionally tried to land at the airport while the visibility was limited to few metres due to darkness.

Buffalo Airways’ initial investigation revealed the engine oil scavenge pump had failed. No TSB-BST investigation was conducted on the event.

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 airplane's unmanageable right yaw during takeoff for reasons that could not be determined because postaccident examination of the rudder and rudder assembly did not reveal any anomalies that would have precluded normal operation.