Sindh (سنڌ سندھ)

The investigation therefore, concludes that:
- Some internal malfunction of the Propeller Governor Part No. 8210-410 Serial No. 2490719 was the cause of experienced uncommanded auto feather. However, exact cause of the occurrence could not be determined.
- Continuing take off below V1 speed (104kts) after encountering engine malfunction and after takeoff raising flaps below recommended height (400ft AGL) lead to decrease in lift and unsustainability of flight.

The cause of the occurrence was uncontained failure of the 2nd stage disk of LP compressor of Engine # 4 due to fatigue fracture which resulted in in-flight fire and damage to adjacent areas of right wing / flaps to an extent that flight could not be sustained.
The use of mishap engine beyond its manufacturer’s assigned life without assessment and life enhancement by the manufacturer was the cause of its uncontained fatigue failure.

Detailed investigation and analyses of the examinable evidence confirmed that the aircraft had developed some problem with its Engine No.2 (Right) immediately after takeoff which was observed by the cockpit crew as propeller feathering on its own. No concrete evidence could be found which would have led to the engine’s propeller malfunction as observed. The only probable cause of propeller feathering on its own could be the wear & tear of the beta valve leading to beta system malfunction. However, this anomaly at the most could have led to the non availability of one engine and making a safe landing with a single engine since the aircraft was capable of landing with a single engine operation. Some of the actions by the cockpit crew before takeoff and subsequent to the observed anomaly in the Engine No.2 were not according to the QRH / FCOM which aggravated the situation and resulted into the catastrophic accident.
The following factors contributed to the accident:
The aircraft accident took place as a result of combination of various factors which directly and indirectly contributed towards the causation of accident.
The primary cause of accident includes, inappropriate skill level of Captain to handle abnormal operation of engine No 2 just after takeoff, failure of cockpit crew to raise the landing gears after experiencing the engine anomaly, execution of remedial actions by FO before the attainment of minimum safe altitude of 400 ft AGL resulted in non conformance and non compliance of cockpit crew to OEM recommended procedures to handle such situations.
The lack of situational awareness and CRM failure directly contributed towards ineffective management of the flight deck by the cockpit crew.
The contributory factors include inadequate cockpit crew simulator training monitoring mechanism both at operator and CAA Pakistan levels in respect of correlation of previous / current performance and skill level of cockpit crew during the simulator training sessions along with absence of conduct of recurrent / refresher simulator training between two annual simulator checks in accordance with ICAO Annex-6 guidelines and CAA Pakistan (applicable ANOs) requirements for specific type of aircraft in a year.

The Pakistan board of investigations determined that the probable cause of this accident was a structural failure due to overload. The aircraft weight was 7,183 lbs at the time of the accident as the maximum load as mentioned in the operational manual is 6,300 lbs, which means 883 pounds above max gross weight. It is believed that during climbout, the tail and stabilizers detached due to overload conditions.

It was determined that the crew failed to prepare the flight according to published procedures. The mass and balance sheet was incorrect. At the time of the accident, the total weight of the aircraft was six tons above MTOW and the CofG as too far forward.

It was determined that all four engines lost power in-flight after hail accumulated in the oil tanks.

Loss of directional control as the result of inadvertent application of forward thrust on n°4 engine at the time the pilot flying was coming out of reverse thrust on engines n°1, 2 and 3 during the landing roll, and subsequent failure of the crew to recognize the asymmetric power condition. Contributing were failure of the crew to monitor the engines, and failure to follow specified procedures during the landing.