ATR42-500

During the takeoff roll from Serui-Stevanus Rumbewas Airport Runway 28, the crew decided to abort for unknown reasons. The airplane veered off runway to the left. While contacting soft ground, it lost its undercarriage and slid for few dozen metres before coming to rest nearby a wooded area. All 48 occupants evacuated safely. The airplane landed at 1019LT from Biak and was taking off for its last leg to Jayapura when the accident occurred.

On final approach to Bukoba Airport, the crew encountered poor visibility due to heavy rain falls. In circumstances that need to be clarified, the airplane descended too low, impacted the water surface and crashed into Lake Victoria, about 100 metres short of runway 31. Fishermen with several boats were quickly on the scene and were able to evacuate 24 people. Unfortunately, 19 others including both pilots were killed. The aircraft sank by a depth about 3-4 metres.

Following an uneventful flight from Islamabad, the crew was cleared to land on runway 25 at Gilgit Airport. After touchdown, the crew initiated the braking procedure but the aircraft was unable to stop within the remaining distance. It overran, lost its right main gear and came to rest 12 metres further in a grassy area. All 53 occupants evacuated safely and the aircraft was damaged beyond repair.

On 07 December 2016 morning, after a routine daily inspection at Benazir Bhutto International Airport (BBIAP) Islamabad, Pakistan International Airlines (PIA) aircraft ATR42-500 Reg No AP-BHO operated 05 flights (ie Islamabad to Gilgit and back, Islamabad to Chitral, Chitral to Peshawar and back). As 6th and last flight of that day, it took off from Chitral at time 10:38:50 UTC (15:38:50 PST) with 42 passengers (including 01 engineer) and 05 crew members (03 pilots and 02 cabin crew) aboard for Islamabad. It crashed after 42 minutes of flight at 11:20:38 UTC (16:20:38 PST) about 3.5 Nautical Miles (NM) SSE of Havelian, and 24 NM North of BBIAP Islamabad. All 47 souls aboard were fatally injured. The aircraft remained in air for about 42 minutes before crash (all timings in UTC). These 42 minutes have been split into three stages of flight, described hereunder:

(a) Initial Stage: From 10:38 to 11:04 (~26 minutes) degraded speed governing accuracy of the port propeller was evident in the DFDR data, but was apparently not observed by the cockpit crew. The flight stabilized at an altitude 13,500 feet AMSL and a cruising speed of 186 knots IAS (instead of expected 230 knots IAS). There were two latent pre-existing technical anomalies in the aircraft (a Fractured / dislodged PT-1 blade due to a known quality issue and a fractured pin inside the OSG), and one probable latent pre-existing condition (external contamination) inside the PVM of No 1 Engine. Digital Flight Data Recorder (DFDR) analysis indicates that No 1 Engine was degraded.

(b) Middle Stage (Series of Technical Malfunctions): From 11:04 to 11:13 (~09 minutes), a series of warnings and technical malfunctions occurred to No 1 Engine (left side) and its related propeller control system. These included Propeller Electronic Control (PEC) fault indications, followed by No 1 Engine power loss, and uncontrolled variation of its propeller speed / blade pitch angle abnormal system operation). The propeller speed which was initially at 82% (cruise setting) decreased gradually to 62% and later at the time of engine power loss it increased to 102% (and stayed at that value for about 15 to 18 seconds). It then reduced down to Non Computed Data (NCD) as per DFDR. At this point, (based on simulation results) the blade pitch angle increased (possibly close to feather position). Later, the propeller speed increased to 120% to 125% (probably caused due to unusual technical malfunctions) and stayed around that value for about 40 to 45 seconds. It finally showed an abrupt drop down to NCD again. At this point, (based on simulation results) the blade pitch angle may have settled at a value, different from the expected feathered propeller. During this unusual variation of propeller speed, there were drastic variations in the aircraft aerodynamic behaviour and sounds. The directional control was maintained initially by the Auto-Pilot. A relatively delayed advancement of power (of No 2 Engine) post No 1 Engine power loss, reduction of power (of No 2 Engine) for about 15 seconds during the timeframe when left propeller rpm was in the range of 120% to 125%, and once again a reduction of power towards the end of this part of flight, were incorrect pilot actions, and contributed in the IAS depletion. Auto-Pilot got disengaged. Towards the end of this part of flight, the aircraft was flying close to stall condition. No 1 Engine was already shutdown and No 2 Engine (right side) was operating normal. At this time, IAS was around 120 knots; aircraft started to roll / turn left and descend. Stick shaker and stick pusher activated. Calculated drag on the left side of the aircraft peaked when the recorded propeller speed was in the range of 120% to 125%. During transition of propeller speed to NCD, the additional component of the drag (possibly caused due to abnormal behaviour of left propeller) suddenly reduced. The advancement of power of No 2 Engine was coupled with excessive right rudder input (to counter the asymmetric condition). This coincided with last abrupt drop in the propeller speed. As a combined effect of resultant aerodynamic forces aircraft entered into a stalled / uncontrolled flight condition, went inverted and lost 5,100 feet AMSL altitude (ie from ~13,450 feet to 8,350 feet AMSL).

(c) Final Stage: The final stage of flight from 11:13 to 11:20 (~07 minutes) started with the aircraft recovering from the uncontrolled flight. Although blade pitch position was not recorded (in the DFDR – by design), and it was not possible to directly calculate that from the available data, a complex series of simulations and assumptions estimated that the blade pitch of left propeller may have settled at an angle around low pitch in flight while rotating at an estimated speed of 5%. Aircraft simulations indicated that stable additional drag forces were present on the left side of the aircraft at this time and during the remaining part of flight. Aircraft had an unexpected (high) drag from the left side (almost constant in this last phase); the aircraft behavior was different from that of a typical single engine In Flight Shutdown (IFSD) situation. In this degraded condition it was not possible for the aircraft to maintain a level flight. However, that level of drag did not preclude the lateral control of the aircraft, if a controlled descent was initiated. The aircraft performance was outside the identified performance envelope. It was exceptionally difficult for the pilots to understand the situation and hence possibly control the aircraft. Figure hereunder shows different stages of flight.

During the takeoff roll from Coari-Urucu Airport by night, the aircraft collided with a tapir that struck the right main gear. The crew continued the takeoff procedure and the flight to Manaus. After two hours and burning fuel, the aircraft landed at Manaus-Eduardo Gomes Airport. Upon touchdown, the right main gear collapsed and the aircraft veered to the right and came to rest. All 49 occupants evacuated safely while the aircraft was damaged beyond repair.

Following an uneventful flight from Islamabad, the crew started the descent to runway 36R in marginal weather conditions. Upon touchdown on a wet runway, the right main gear collapsed. The aircraft slid for about 1,700 feet before exiting the runway to the right and coming to rest 60 feet further on. All 46 occupants were unhurt while the aircraft was considered as damaged beyond repair. Five minutes after the accident, the weather briefing was as follow: OPLA 311015Z 16009KT 3000 RA BKN040 OVC100 29/24 Q1003. But ten minutes prior to the crash, the weather briefing was as follow: OPLA 311000Z 33008KT 4000 -RA SCT040 BKN100 32/24 Q1002 TEMPO 31030KT 2000 TSRA FEW030CB. Thus, the conditions were considered as marginal with turbulences, wind to 30 knots and CB's at 3,000 feet. On 11SEP2012, the French BEA reported that the aircraft touched down just at the beginning of the paved surface (undershoot area) to the right of the extended runway 36R centerline, causing the right main gear to collapse. It was reported that the aircraft was unstable on short final and that the crew failed to initiate a go-around procedure while the aircraft was too low on the glide.