When the horizon lied

If you were a visitor to Juhu beach in Mumbai on the 1st of January 1978, at about 8:30 pm, the evening sky would have displayed the majestic Boeing 747 take-off from Mumbai airport. An aircraft that symbolized the aspirations of a developing nation. You would have observed the airplane make a right turn after crossing the coast and then flying wings level momentarily. As you follow the airplanes trajectory, for no apparent reason it suddenly veers to the left and and spirals into the Arabian Sea. As you gasp in horror at the sight of this mighty airplane disintegrating into a thousand pieces, you have witnessed one of the deadliest accidents in Indian aviation history. It was a blow that resonated far beyond the aviation community.

The two protagonists…

Attitude Indicator: An Instrument in the airplane which replicates the Horizon. Also called The Artificial Horizon. In this case without any visual cues of the actual horizon the instruments failure proved fatal.

Leans: A common illusion in aviation that causes a pilot to feel like they are leaning to one side, even though the aircraft is level.

The vestibular system in the inner ear is responsible for the sense of balance in human beings. The Vestibular system consists of three semicircular canals which recognize acceleration in pitch bank and yaw. These canals are filled with fluid and have tiny hair follicles. As the fluid moves in the direction of acceleration it moves the hair follicles which sends information about the direction of turning to the brain. Remember childhood days riding on the merry go round and remember your head spinning in the direction of the turn even after the wheel stopped, that’s exactly how the leans feel like.

Emperor Ashoka, the 7-year-old Boeing 747 was ready for an evening departure to Dubai. In the cabin were 190 passengers and 20 crew. In the cockpit were the captain, the first officer and the flight engineer. The captain who was flying the airplane made a scheduled turn to the right after departing from runway 27 from Mumbai. As the captain straightened the airplane into wings level from this turn. He found the Attitude Indicator was still indicating a right turn. (unknown to the captain the instrument had failed). With the instrument showing a right bank and his Inner Ear giving him the Leans indicated a right turn just like his attitude Indicator. Without any visual cues of the actual horizon, having taken off into the night sky his only reference were the attitude indicator and his inner ear senses, and both indicated the airplane was still on a right bank. He tried to correct the situation by banking the airplane to the left but there was no response from the failed artificial horizon. As the captain in command he instinctively banked the airplane further to the left unaware of the fatal error. Little did he know that the instrument and his inner ear senses were giving him wrong indications. He pushed the airplane into a steep bank of 110 degrees, the massive 747 would have groaned in protest and shuddered violently moments before she slammed into the Arabian sea and disintegrated on impact, instantly killing all 213 people. Although the first officer could have prevented this catastrophe because his instrument was indicating correctly, but was not clear in his communication and the engineer’s inputs were too late. The investigation board blamed the captain for irrational control inputs.

The tragic mix of Instrument failure, human limitations and the deceptive power of the night sky was not really explored too deeply at that time. Studies and new understanding about the functioning of the human brain today helps us deal with these kinds of events with a different approach. Modern innovations in ergonomics and redundancy of instruments ensures that such tragedy would not be repeated.