Investigation Summary
The accident was precipitated by a failure of the SAY-2000 electronic engine control unit, which caused the right engine (No. 2) to shut down just as the aircraft reached rotation speed. The aircraft was operating in 35°C heat and was approximately 190 kg over the maximum takeoff weight the crew had calculated using confusing performance charts in the Aircraft Flight Manual (AFM). However, the actual safe limit for the ambient conditions was much lower, meaning the aircraft was effectively 2,666 kg overweight for a safe single-engine climb. Furthermore, the crew had selected 10 degrees of flaps instead of the required 15 degrees and failed to properly set the elevator and rudder trim. Following the engine failure, the crew did not manually feather the propeller, and the automatic feathering system suffered a 17-second delay. During this period, the unfeathered propeller created significant negative thrust (drag). The pilot's attempt to gain altitude by increasing the pitch, combined with the failure to retract the landing gear, the incorrect flap settings, and high drag, led to an aerodynamic stall at a height of approximately 40 meters.
Final Conclusions
The AAIB Iran concluded the primary cause was the simultaneous failure of the SAY-2000 electronic engine control and the No. 2 engine shutdown during the takeoff roll. A major contributing factor was the confusing AFM performance charts which caused the pilots to significantly overestimate the aircraft's Maximum Take-Off Mass (MTOM); while the crew believed they were only 190 kg over the limit, the aircraft was actually 2,666 kg over the safe performance limit for the 35°C ambient temperature. Other factors included the crew's failure to manually feather the propeller, rotating below the recommended speed, the failure to retract the landing gear, and the presence of negative thrust from the unfeathered propeller which had not been adequately accounted for during aircraft certification.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
63 years old; held An-140 certificate since May 2014.
First Officer
32 years old; acting as pilot not-flying.
Systems & Failure Modes
SAY-2000
The electronic engine control system which failed, causing the engine shutdown and delaying the feathering of the propeller.
Klimov TV3-117VMA-SBM1
The turboprop engine model; the right engine failed during the takeoff roll.
Propeller Feathering System
Designed to turn propeller blades parallel to the airflow to reduce drag; it failed to activate automatically for 17 seconds.
Interesting Facts
- 01The aircraft was an Iranian-assembled version of the Antonov An-140, known as the HESA IrAn-140.
- 02The aircraft was 2,666 kg over the safe takeoff weight for the ambient temperature, though pilots believed they were only 190 kg over due to confusing manual charts.
- 03The right engine had a history of malfunctions, including two failures in April 2014 and violent shaking three days before the crash.
- 04The investigation found that the aircraft's fuel load was 500 kg more than required for the flight.
- 05The 48 souls on board consisted of 42 passengers (including 2 off-duty mechanics) and 6 crew members (2 pilots and 4 flight attendants).
- 06A total of 40 occupants were killed: 34 passengers and all 6 crew members.
Safety Actions & Advisories
Grounding of IrAn-140 Fleet
Following the accident, President Hassan Rouhani ordered the grounding of all HESA IrAn-140 aircraft in Iran pending a full investigation.
AFM Revision
Investigators recommended a complete overhaul of the Aircraft Flight Manual to remove ambiguities in performance calculations and takeoff weight limits.
Known Controversies & Unanswered Questions
Three-Way Investigative Dispute
Reference ↗The investigation involved conflicting views between Iran's CAO, Ukrainian investigators, and the Interstate Aviation Committee (IAC) regarding the reliability of the SAY-2000 system and the extent of pilot error versus design flaws.