Mumbai-Brussels flight, carrying 280 passengers, dropped 2,251 ft before correcting course while captain was resting, co-pilot was in charge.
The co-pilot of a Jet Airways flight that plunged 2,251 feet over Turkey before correcting course last year "inadvertently manipulated" the controls, resulting in the incident, according to an inquiry by aviation regulator DGCA.
The Mumbai-Brussels flight, with 280 passengers aboard, suddenly lost altitude on August 8, 2014, when the 46-year-old co-pilot was in charge. The 40-year-old fight captain was sleeping as permitted under cockpit rules.
The Air Traffic Control in the Turkish capital of Ankara cautioned the co-pilot when the plane began to drop altitude, flying below 32,000 feet. Most passenger planes cruise at an altitude in the range of 30,000 feet to 40,000 feet, and the Jet flight was cleared to fly at 34,000 feet.
The aircraft, a Boeing 777-300 ER, had flown 4 hours and 43 minutes when the incident took place.
Initial reports after the incident had said that the plane plunged 5,000 feet, but investigations showed that it fell 2,251 feet before corrective measures were taken. The reports had also said that the co-pilot was busy using a tablet computer, called an electronic flight bag by airlines, but the DGCA report has no mention of it.
The final-investigation report by Sanjay Bramhane, DGCA's deputy director for air safety (western region), states that the flight started to lose altitude after the co-pilot accidentally changed controls while working on some other settings.
After the Ankara ATC alerted him, he pressed the altitude hold button on the control panel and the flight climbed back 32,000 feet. He then woke up the captain, who noticed a reading of 29,200 feet on the flight management computer.
The co-pilot should have ideally first alerted the captain instead of correcting the flight's course on his own. A first officer is not required to make unsupervised altitude changes while the captain is resting. "The first officer did not feel any abnormal condition of dropping altitude, and decided to correct the flight level by initiating climb without bringing it to the notice of the resting commander," the report states.
The presence of a cabin crew member in the cockpit while the captain is resting can prevent such incidents, it adds. Bramhane recommended corrective training on flight automation systems for the co-pilot.
As part of the probe, the aviation regulator examined training records of the co-pilot to ascertain if there were any lapses by him or instructors during refresher flying exercises and other courses. No lapses were found.