On 10 August 2014, the Number 2 engine of an Antonov 140-100 (EP-GPA) being operated by Sepahan Airlines from Tehran Mehrabad to Tabas as flight 5915 failed just as the aircraft was about to become airborne from runway 9L. Once airborne, the aircraft was seen to diverge to the right of the runway centreline but reached only a low height before descending, right wing down, and crashing within a nearby industrial complex. The effects of the impact and a post crash fire destroyed the aircraft and 40 of the 48 occupants, including all 6 crew members, died at the time of the crash or subsequently from the injuries sustained in it. The remaining 8 occupants sustained serious injuries but survived. Some collateral damage to structures and trees at the crash site occurred.
An Investigation was carried out by the Iran Civil Aviation Organisation (CAO) Accident Investigation Board (AAIB). The CVR and FDR were recovered and their data were successfully downloaded and used to assist the Investigation. It was noted that the prevailing weather conditions had been good and had not had any direct bearing on accident causation.
It was noted that the 63 year-old Captain, who had been PF for the accident flight, had 9,478 total flying hours which included 2,000 hours on type. The 32 year-old First Officer had 572 total flying hours which included about 400 hours on type. It was also noted that the An-140 aircraft involved had been assembled in Iran by the Iran Aircraft Manufacturing Industrial Company (HESA).
It was established that immediately prior to the accident flight, the crew had begun their duty day by operating the same aircraft from Isfahan to Tehran. The accident takeoff from the 4,300 metre-long runway 29L had been made with Flap 10°and had proceeded uneventfully until just after the V1 call by the First Officer when, passing 116 knots with 5 knots to go below the applicable Vr, the first signs of malfunction of the No 2 engine became apparent. As it ran down, No 1 engine power was automatically increased to the 'contingency' setting where it remained until the aircraft eventually stalled and crashed less than a minute later having reached a maximum height of only 130 feet. After what was identified as a marginally premature rotation, takeoff was continued with FDR data showing that the angle of attack had been above AFM recommendations (4-7°) and that airspeed, which never reached V2, had "continually reduced". The landing gear was not retracted.
It was established that the failure of the No 2 engine had been caused by a temporary (17 second) malfunction of its electronic engine controller (EEC) which had resulted in the engine being starved of fuel. Because of this, the continuous aural and visual warning of engine failure did not begin until about 14 seconds after the failure but CVR data showed the Captain had detected and called it after 5 seconds. However, it was found that the crew had not then manually feathered the failed engine propeller by pressing the 'ENGINE OFF - FEATHER' button as required by the AFM and a further consequence of the failure of the EEC had been that it did not detect the failure and had therefore not signalled that it should be shut down and its propeller feathered. This only happened when the No 2 engine EEC began to function normally again as the aircraft was recorded as climbing through 30 feet agl. Meanwhile, the Captain had begun corrective left rudder inputs but despite this, the aircraft began to deviate to the right of the runway extended centreline - see the ground track illustration below. Once the right engine propeller had been automatically feathered by the EEC, the aircraft remained airborne for a further 30 seconds, but as the angle of attack had reached 12°, pitch control had eventually been lost and an aerodynamic stall had immediately preceded ground impact. It was noted that the First Officer had declared the emergency status to ATC at about the time the delayed engine failure warning had commenced but by this time ATC were already aware that the departure was not proceeding normally having observed the deviation to the right and a poor climb rate.
An annotated aircraft ground track - the poor quality of some text is a function of the source. [Reproduced from the Official Report]
In respect of the EEC malfunction which delayed full feathering of the failed engine propeller, the Investigation found that such malfunctions had been "the main cause of several previous accidents and incidents" and that although the component designer had "performed some modifications and software improvements to rectify the malfunction […] the failure rate […] was not reduced to acceptable levels".
Various other matters were examined and their relevance either confirmed, noted or dismissed. These included:
- There was no evidence to suggest that either pilot was fatigued.
- There was no evidence to suggest that wake vortex turbulence from the Boeing MD-88 which had departed 29L ahead of the accident aircraft had affected its controllability as the transition to single-engine flight was made.
- The departure flap setting of 10° was not appropriate for an aircraft taking off with a mass in the vicinity of MTOM and in any case, the aircraft operator did not have regulatory approval to use it at all.
- The Captain was aware that the takeoff was being conducted with the aircraft marginally overweight.
- A number of concerns in respect of the (original) aircraft type certification by both the IAC and Ukraine were identified as were concerns about the calculation of MTOM according to the AFM and its procedure for getting airborne with one engine inoperative. In the case of the MTOM, it was considered that "the confusing performance chart in the AFM" had led to the pilots making a performance calculation that significantly overestimated the aircraft MTOM for the accident flight. In the case of a single engine climb out, it was considered that the procedure in the AFM was "not clear" since it required the achievement of V2 before the landing gear could be retracted.
- As a result of the occurrence of a range of defects other than the EEC affecting the reliability of the engines fitted to An-140 aircraft, including "fuel pump plunger gaps, compressor blade corrosion and erosion, turbine blade melting", operation of the aircraft type at the time of the investigated accident, had been restricted by the Iran CAO to operations in the southern part of Iran based on climate (density altitude) considerations. However, no link was made between the problems which had led to this restriction and the cause of the accident.
The Investigation also found that although ATC activated the crash alarm promptly, poor coordination and an incorrect report of the location of the crash site led to the Airport RFFS reaching the aircraft after the City Firefighting team who had turned up after receiving direct calls from members of the public who had seen the crash. It was found that all those who survived had escaped from the wreckage of the aircraft unaided prior to the arrival of any emergency services. It was also noted that the Airport had failed to provide a timely alert to the Tehran Rescue Organisation as required in the Airport Emergency Plan.
The Conclusion of the Investigation was that the Main Cause of the accident was "a combination of the failure of the Electronic Engine Control (SAY-2000) simultaneously with the (uncommanded) shut down of engine No 2 about 2 seconds before aircraft lift-off and a confusing performance chart in the AFM which led to the pilots relying on a performance calculation that significantly over-estimated the aircraft MTOM".
Three Contributory Factors were also identified as follows:
- Unclear content in the Aircraft Flight Manual including the procedure for calculating the maximum allowable take-off weight, VR and V2 and ambiguity in the climb segment definition and applications.
- Crew performance, including:
- The Captain's rotation of the aircraft at a speed of about 118 knots whereas 121 knots is the speed recommended in the AFM table 4.2.3.
- The crew failure to perform the manual propeller feathering procedure for the failed engine.
- The Captain's decision to fly with the aircraft despite his awareness that it was about 190 kg overweight.
- The Captain's decision to load about 500 kg more fuel than was required for the accident flight.
- The appearance of negative thrust from the unfeathered propeller blades at takeoff were not considered during the aircraft certification tests, as it was considered improbable. However, in the accident flight the negative thrust did appear and affected aircraft performance.
A total of 24 Safety Recommendations were made as follows:
- that the Iran Civil Aviation Organisation (CAO) should analyse, in conjunction with aircraft designer & manufacturer, the information obtained in this accident Investigation and its related findings to evaluate the adequacy of certification standards and test methods specified in the State regulatory requirements and guidance materials especially for the aircraft and engine type validation process. If appropriate, certification standards should be modified and the compliance of the An-140-100 aircraft and its engine in respect of CAO airworthiness requirements relevant to the findings of the Investigation should be re-evaluated.
- that the Iran Civil Aviation Organisation (CAO) should re-evaluate the maintenance procedure regarding engine vibration rectification in conjunction with aircraft/engine designer and manufacturer.
- that the Iran Civil Aviation Organisation (CAO) should re-evaluate their oversight of (safety) regulation and take any necessary action to improve their surveillance and monitoring when the rate of (occurrence of a particular) failure grows.
- that the Iran Civil Aviation Organisation (CAO) should take necessary action to ensure that the Manual of Air Traffic Services (MATS) is reviewed and revised according to ICAO Doc 4444.
- that the Iran Civil Aviation Organisation (CAO) should take necessary action to establish and implement necessary requirements for Aerodrome Certification.
- that the Iran Civil Aviation Organisation (CAO) should take the necessary action to implement SMS at the Iranian Airport Company, related airports and the Tehran Area Control Centre.
- that HESA and Sepahan Airlines should revise the aircraft loading procedure and agreements with ground handling service providers to comply with CAO requirements.
- that HESA and Sepahan Airlines should revise Sepahan Airlines SOPs to add the procedure for flight with Flap 10°.
- that HESA and Sepahan Airlines should revise the An-140-100 pilot training program and ensure it is followed.
- that HESA and Sepahan Airlines should fully implement Iran CAO maintenance and continuing airworthiness requirements.
- that the State of Design (Ukraine) and the State of Manufacture (Iran) should review and revise the An-140-100 AFM taking into account performance charts, take-off climb segment, OEI procedures and so on.
- that the State of Design and the State of Manufacture should review and revise the An-140-100 AMM and correct related charts and procedure.
- that the State of Design and the State of Manufacture should take appropriate action to rectify SAY-2000 (EEC) malfunctions and (related) poor engine reliability.
- that the State of Design and the State of Manufacture should take appropriate action to reduce the aircraft empty weight to pre-determined design criteria.
- that the State of Design and the State of Manufacture should take appropriate action in order to ensure that the automatic propeller feathering system complies with related airworthiness requirements. It should be modified in order to be capable of operating in its intended manner at the time of engine failure with no special operations necessary on the part of the crew in order to make the automatic feathering system operative.
- that the State of Design and the State of Manufacture should develop an An-140 training regime that will ensure that flight crew have a full understanding of weight calculation, manual engine control modes and aircraft performance through improved documentation, courseware, and instructor training.
- that the State of Design and the State of Manufacture should take appropriate action in order to ensure that Antonov conducts tests to support the development of recommendations for flight crews as to their actions if there appears to be negative thrust from unfeathered propeller blades in the case of engine failure at takeoff.
- that the Iranian Airport Company should review and revise the Manual of Air Traffic Services (MATS) according to ICAO Doc4444.
- that the Iranian Airport Company and Mehrabad Airport should take appropriate action, including necessary training for controllers to carefully watch-out and watch-in the flight path of aircraft during landing and departure.
- that the Iranian Airport Company, Mehrabad Airport and the Aircraft Rescue and Firefighting Working Group should review the Mehrabad Airport emergency plan and clarify task sharing between the airport fire fighting unit and other parties.
- that the Iranian Airport Company, Mehrabad Airport and the Aircraft Rescue and Firefighting Working Group should communicate the airport emergency plan and related training and exercises should be held at least annually according to the approved time frame.
- that Mehrabad Airport should use the baggage weighing facilities at passenger check-in gates at departure terminal which have the capability of weight recording.
- that the Iranian Airport Company should take the necessary action to obtain an Aerodrome Certificate for Mehrabad Airport.
- that the Iranian Airport Company should develop, implement and maintain a Safety Management System (SMS) within the company which includes Mehrabad Airport and Tehran Area Control Centre (ACC).
The Final Report of the Investigation was adopted and issued on 9 August 2017.