Scheduled Revenue Flight

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.

On October 28, 2016, about 1432 central daylight time, American Airlines flight 383, a Boeing 767-323, N345AN, had started its takeoff ground roll at Chicago O’Hare International Airport, Chicago, Illinois, when an uncontained engine failure in the right engine and subsequent fire occurred. The flight crew aborted the takeoff and stopped the airplane on the runway, and the flight attendants initiated an emergency evacuation. Of the 2 flight crewmembers, 7 flight attendants, and 161 passengers on board, 1 passenger received a serious injury and 1 flight attendant and 19 passengers received minor injuries during the evacuation. The airplane was substantially damaged from the fire. The airplane was operating under the provisions of 14 Code of Federal Regulations Part 121. Visual meteorological conditions prevailed at the time of the accident. The uncontained engine failure resulted from a high-pressure turbine (HPT) stage 2 disk rupture. The HPT stage 2 disk initially separated into two fragments. One fragment penetrated through the inboard section of the right wing, severed the main engine fuel feed line, breached the fuel tank, traveled up and over the fuselage, and landed about 2,935 ft away. The other fragment exited outboard of the right engine, impacting the runway and fracturing into three pieces. Examination of the fracture surfaces in the forward bore region of the HPT stage 2 disk revealed the presence of dark gray subsurface material discontinuities with multiple cracks initiating along the edges of the discontinuities. The multiple cracks exhibited characteristics that were consistent with low-cycle fatigue. (In airplane engines, low-cycle fatigue cracks grow in single distinct increments during each flight.) Examination of the material also revealed a discrete region underneath the largest discontinuity that appeared white compared with the surrounding material. Interspersed within this region were stringers (microscopic-sized oxide particles) referred to collectively as a “discrete dirty white spot.” The National Transportation Safety Board’s (NTSB) investigation found that the discrete dirty white spot was most likely not detectable during production inspections and subsequent in-service inspections using the procedures in place. The NTSB’s investigation also found that the evacuation of the airplane occurred initially with one engine still operating. In accordance with company procedures and training, the flight crew performed memory items on the engine fire checklist, one of which instructed the crew to shut down the engine on the affected side (in this case, the right side). The captain did not perform the remaining steps of the engine fire checklist (which applied only to airplanes that were in flight) and instead called for the evacuation checklist. The left engine was shut down as part of that checklist. However, the flight attendants had already initiated the evacuation, in accordance with their authority to do so in a life-threatening situation, due to the severity of the fire on the right side of the airplane.

During the takeoff roll from runway 15/33 at Dire Dawa-Aba Tenna Dejazmach Yilma Airport, the aircraft collided with wild animals. The captaint abandoned the takeoff procedure and initiated an emergency braking manoeuvre when the aircraft veered off runway and came to rest. All 80 occupants evacuated safely and the aircraft was damaged beyond repair.

On final approach to Belaya Gora Airport, the aircraft was too low and hit the ground. On impact, the right main gear and the nose gear collapsed. The aircraft slid for several yards before coming to rest in a snow covered field about 400 meters short of runway threshold and 300 meters to the left of the approach path. The propeller on the right engine was torn off and it appears that the fuselage was bent as well. All 33 occupants were evacuated safely. At the time of the accident, weather conditions were marginal with limited visibility caused by snow falls. It was reported the visibility was about 2,5 km at the time of the accident while the crew needed at least 4 km on an NDB approach.

On October 2, 2016, about 1157 Alaska daylight time, Ravn Connect flight 3153, a turbine powered Cessna 208B Grand Caravan airplane, N208SD, collided with steep, mountainous terrain about 10 nautical miles northwest of Togiak Airport (PATG), Togiak, Alaska. The two commercial pilots and the passenger were killed, and the airplane was destroyed. The scheduled commuter flight was operated under visual flight rules by Hageland Aviation Services, Inc., Anchorage, Alaska, under the provisions of Title 14 Code of Federal Regulations Part 135. Visual meteorological conditions prevailed at PATG (which had the closest weather observing station to the accident site), but a second company flight crew (whose flight departed about 2 minutes after the accident airplane and initially followed a similar route) reported that they observed unexpected fog, changing clouds, and the potential for rain along the accident route. Company flight-following procedures were in effect. The flight departed Quinhagak Airport, Quinhagak, Alaska, about 1133 and was en route to PATG.

The twin engine aircraft departed Goma on a regular schedule flight (service UNO830) to Beni, carrying eight passengers and two pilots on behalf of the Monusco, the United Nations Organization Stabilization Mission in the Democratic Republic of Congo. On approach to Beni-Mavivi Airport, the crew completed the approach checklist and elected to configure the aircraft but realized that the undercarriage would not extend. After the circuit breaker was reset, the crew was able to lower the landing gear manually and continued the approach with no reporting to ATC. After touchdown on runway 11, the aircraft rolled for about 450 metres when the right main gear collapsed. Out of control the aircraft veered off runway to the right, slid in a grassy area, crossed a ditch and came to rest near the apron. All 10 occupants evacuated safely and the aircraft was damaged beyond repair.

The approach to Siddharthanagar-Gautam Buddha Airport was completed in good weather conditions with a wind from the southeast at 4 knots and a 8 km visibility. After touchdown on runway 28, the twin engine aircraft was unable to stop within the remaining distance. It overran, lost its undercarriage and came to rest in bushes, some 110 metres past the runway end. All 32 occupants evacuated safely and the aircraft was damaged beyond repair.

The Cessna had departed about 3 minutes prior on a scheduled passenger flight and the Piper was en route to a remote hunting camp when the two airplanes collided at an altitude about 1,760 ft mean sea level over a remote area in day, visual meteorological conditions. The airline transport pilot and two passengers onboard the Cessna and the commercial pilot and the passenger onboard the Piper were fatally injured; both airplanes were destroyed. Post accident examination revealed signatures consistent with the Cessna's outboard left wing initially impacting the Piper's right wing forward strut while in level cruise flight. Examination revealed no mechanical malfunctions or anomalies that would have precluded normal operation of either airplane. Neither pilot was in communication with an air traffic control facility and they were not required to be. A performance and visibility study indicated that each airplane would have remained a relatively small, slow-moving object in the other pilot's window (their fuselages spanning less than 0.5° of the field of view, equivalent to the diameter of a penny viewed from about 7 ft away) until about 10 seconds before the collision, at which time it would have appeared to grow in size suddenly (the "blossom" effect). From about 2 minutes before the collision, neither airplane would have been obscured from the other airplane pilot's (nominal) field of view by cockpit structure, although the Cessna would have appeared close to the bottom of the Piper's right wing and near the forward edge of its forward wing strut. The Cessna was Automatic Dependent Surveillance-Broadcast (ADS-B) Out equipped; the Piper was not ADS-B equipped, and neither airplane was equipped with any cockpit display of traffic information (CDTI). CDTI data would have presented visual information regarding the potential conflict to both pilots beginning about 2 minutes 39 seconds and auditory information beginning about 39 seconds before the collision, providing adequate time for the pilots to react. The see-and-avoid concept requires a pilot to look through the cockpit windows, identify other aircraft, decide if any aircraft are collision threats, and, if necessary, take the appropriate action to avert a collision. There are inherent limitations of this concept, including limitations of the human visual and information processing systems, pilot tasks that compete with the requirement to scan for traffic, the limited field of view from the cockpit, and environmental factors that could diminish the visibility of other aircraft. Given the remote area in which the airplanes were operating, it is likely that the pilots had relaxed their vigilance in looking for traffic. The circumstances of this accident underscore the difficultly in seeing airborne traffic by pilots; the foundation of the "see and avoid" concept in VMC, even when the cockpit visibility offers opportunities to do so, and particularly when the pilots have no warning of traffic in the vicinity. Due to the level of trauma sustained to the Cessna pilot, the autopsy was inconclusive for the presence of natural disease. It was undetermined if natural disease could have presented a significant hazard to flight safety.

On 3 August 2016, an Emirates Boeing 777-31H Aircraft, registration A6-EMW, operating a scheduled passenger flight UAE521, departed Trivandrum International Airport (VOTV), India, at 0506 UTC for a 3 hour 30 minute flight to Dubai International Airport (OMDB), the United Arab Emirates, with 282 passengers, 2 flight crew and 16 cabin crew members on board. The Commander attempted to perform a tailwind manual landing during an automatic terminal information service (ATIS) forecasted moderate windshear warning affecting all runways at OMDB. The tailwind was within the operational limitations of the Aircraft. During the landing on runway 12L at OMDB the Commander, who was the pilot flying, decided to fly a go-around, as he was unable to land the Aircraft within the runway touchdown zone. The go-around decision was based on the perception that the Aircraft would not land due to thermals and not due to a windshear encounter. For this reason, the Commander elected to fly a normal go-around and not the windshear escape maneuver. The flight crew initiated the flight crew operations manual (FCOM) Go-around and Missed Approach Procedure and the Commander pushed the TO/GA switch. As designed, because the Aircraft had touched down, the TO/GA switches became inhibited and had no effect on the autothrottle (A/T). The flight crew stated that they were not aware of the touchdown that lasted for six seconds. After becoming airborne during the go-around attempt, the Aircraft climbed to a height of 85 ft radio altitude above the runway surface. The flight crew did not observe that both thrust levers had remained at the idle position and that the engine thrust remained at idle. The Aircraft quickly sank towards the runway as the airspeed was insufficient to support the climb. As the Aircraft lost height and speed, the Commander initiated the windshear escape maneuver procedure and rapidly advanced both thrust levers. This action was too late to avoid the impact with runway 12L. Eighteen seconds after the initiation of the go-around the Aircraft impacted the runway at 0837:38 UTC and slid on its lower fuselage along the runway surface for approximately 32 seconds covering a distance of approximately 800 meters before coming to rest adjacent to taxiway Mike 13. The Aircraft remained intact during its movement along the runway protecting the occupants however, several fuselage mounted components and the No.2 engine/pylon assembly separated from the Aircraft. During the evacuation, several passenger door escape slides became unusable. Many passengers evacuated the Aircraft taking their carry-on baggage with them. Except for the Commander and the senior cabin crew member who evacuated after the center wing tank explosion, all of the other occupants evacuated via the operational escape slides in approximately 6 minutes and 40 seconds. Twenty-one passengers, one flight crewmember, and six cabin crew members sustained minor injuries. Four cabin crew members sustained serious injuries. Approximately 9 minutes and 40 seconds after the Aircraft came to rest, the center wing tank exploded which caused a large section of the right wing upper skin to be liberated. As the panel fell to the ground, it struck and fatally injured a firefighter. The Aircraft was eventually destroyed due to the subsequent fire. Following the Accident, the Operator (Emirates), the General Civil Aviation Authority (GCAA), Dubai Airports and Dubai Air Navigation Services (‘dans’) implemented several safety actions. In this Final Report, the AAIS issues safety recommendations addressed to the Operator, the GCAA, The Boeing Company, the Federal Aviation Administration (FAA), Dubai Airports, ‘dans’, and the International Civil Aviation Organization (ICAO).

While taking off from the bay off Jinshan (south of Shanghai), the single engine aircraft collided with a concrete bridge and crashed in the sea. One pilot and four passengers were killed while five other occupants were injured. The seaplane C208 EX version was destroyed. It is believed that the crew misjudged the distance between the departure point and the bridge as the collision occurred just after rotation while attempted a steep climb.