Indian Airlines Flight 491

The crash occurred exactly one day after the hijacking of an Indian Airlines Boeing 737 by a Muslim extremist in Amritsar. As such, there were concerns that Flight 491 had been bombed by terrorists. The Indian Bomb Detection and Disposal Squad was requested to determine whether the aircraft had been sabotaged or not. The investigation immediately ruled out terrorism from the possible cause of the accident as there were neither traces of explosives nor evidence that a bomb explosion had occurred on board.[2]

There were indications that the aircraft had been overloaded. Initially, the load sheet of the flight suggested that the actual take-off weight (ATOW) was 54 kg less than the regulated take-off weight (RTOW). Further investigation revealed that the aircraft had been loaded with 118 kg more than its permitted take-off weight. An overloaded state of the aircraft would have required a longer speed build up, thus explaining the late lift off of Flight 491. However, investigators could not determine the exact weight of the aircraft during takeoff and the exact extent of the overloading due to lack of clear evidence. According to the final report, investigators had to resort to reasonings and guess work.[2]

The investigation revealed that passengers' baggage were "serially numbered but not accounted". Some passengers carried heavy hand baggage into the overhead cabin. It was estimated that the total weight of the hand baggage inside the cabin had exceeded the "calculated in built passenger weight".[2]

Investigators estimated that the aircraft had been overloaded by 1 ton. Indian Airlines argued that the overload wouldn't have exceeded 500 kg. However, First Officer Mohan claimed that the aircraft had been overloaded by 4.65 ton, including a 500 kg overload of cargo due to a 2 degree rise in temperature during the accident.[2]

Three flight simulations were then conducted to confirm the theory. None of the simulations resulted in a crash. The second simulation, however, suggested that Flight 491 might have crashed had the pilot initiated a late rotation, suggesting that the late rotation was directly caused by the pilot rather than the overweight condition. Further calculations concluded that even if the aircraft had been overloaded, particularly in the forward section, the centre of gravity of the aircraft would not have significantly shifted.[2]

Aircraft overload was then ruled out from the possible causes of the crash. However, it contributed to Captain's Singh misperception, which would later cause the crash.[2]

Flight 491 attained its Vr speed within 32 seconds after the crew had initiated the take-off roll, approximately at 4,100 feet (1,200 m) from the beginning of the 6,000-foot (1,800 m) runway. The cockpit voice recorder revealed that the aircraft's rotation was initiated 5–7 seconds after the rotation call. Even though the take-off roll was smooth and the acceleration was normal, the aircraft's nose started to rise approximately at a distance of 500 ft of the runway end and it still didn't manage to lift off when it ran though the 1800 ft additional distance. This could be attributed to the pilot's late rotation or a sudden freak weather condition. As it was hot and clear at the time of the accident, freak weather was immediately ruled out.[2]

When the aircraft overran the 6,000-foot (1,800 m) runway and started to run through the 1,800 feet (550 m) additional runway distance, investigators noted that both Captain Singh and First Officer Mohan didn't react to the abnormality. In fact, Captain Singh stated that it was normal for most of his flights. Investigators later concluded that Captain Singh had adopted a similar take-off pattern to his previous flights, where the take-off was late and the climb gradient was lower than expected.[2]

According to the interview, at the time of the accident, Captain Singh concluded that the actual take-off weight of the aircraft was exceeding its regulated take-off weight. As he thought that an overloaded condition would require a longer time to build up speed, he thought that by delaying the aircraft's rotation, taking a slow rotation or even under-rotation, the speed would eventually build up and the aircraft would acquire greater take-off speed, thus easing the climb. The runway was 6,000 feet (1,800 m) long and the decision to delay the rotation would cause the aircraft's distance to be closer with the road, leading to the collision with the lorry.[2]

When a flight crew had called for a rotation, they should have immediately initiated the rotation. The lorry was first seen approximately six seconds after the rotation call. Had the crew initiated the rotation at an earlier stage with a normal technique, the aircraft would have lifted off approximately 4–5 seconds later and it would have achieved a height of at least 35 ft above the runway. When the rotation was initiated at a late stage and the lorry suddenly came in view, Captain Singh didn't respond for 2 seconds until he finally initiated a fast over-rotation in order to evade a collision. He claimed that he was disoriented and panicked due to the presence of the lorry. He was later noted by investigators as lacking in professionalism.[2]

While First Officer Mohan was initially noted for her lack of response, she was later noted for being aware of an abnormality during the later stage of the take-off roll when she instantaneously grabbed the control column. Captain Singh, however, prevented her, saying "Leave it, leave it".[2]

Adjacent to the runway was a small public road connecting north–south. Prior to the accident, around 1975 - 1985, the road was gated and the gates would be closed whenever there was an aircraft movement in the airport. Since 1986, theses gates didn't exist anymore and thus vehicles could freely use the road at any time.[2]

Traffic regulation for roads in the vicinity of the airport was one of the responsibilities of the Indian National Airport Authority (NAA). Investigators noted that there was communication gap between NAA officials on the traffic regulation, with each officials tried to pass the buck on to the others. It was clear that the NAA at Aurangabad had failed to maintain the airport's vicinity properly.[2]

The final report was published on 25 December 1993. It concluded the cause of the crash as follow:

Causes of the accident were: (i) Pilots' error in initiating late rotation and following wrong rotation technique, and (ii) failure of the NAA to regulate the mobile traffic on the Beed road during the flight hours.[2]

Investigators issued 25 recommendations to the NAA, Aurangabad airport and Indian Airlines. In the aftermath of the crash, the road was gated again. An additional distance of 3,000 ft was added to the runway's length. Captain Singh's Captain license was revoked and his co-pilot license was suspended. Other officials who were involved or deemed as contributing to the accident were ordered to receive "departmental actions". Subsequently, the report asked the senior fire crew, Gosavi, to be awarded due to his quick response on the crash of Flight 491.[2]