A gust of wind, wrong decision by the pilots, the condition of the air strip and even faulty indication by the instrument landing system could be possible reasons for the crash of the Air India Express on Friday in the south Indian city of Kozhikode, according to aviation experts.
The dominant reason cited by the experts was the decision by the pilots to not divert the plane to another airport after the first attempt to land at the designated strip failed amid rain.
The Boeing 737, bringing back 190 stranded Indians from Dubai, broke into pieces after it overshot the table-top runway 10 and fell into a valley 35 feet below, leaving 18 people including both the pilots dead.
"It is foolish to land with a tailwind on a wet runway...This is what I have been pointing out for years. I said in 2011 that landing with a tailwind in rain on runway 10 will result in an accident one day," leading expert Captain Mohan Ranganathan told PTI.
Ranganathan was a member of the operations group of the Civil Aviation Safety Advisory Committee (CASAC) in 2011. He has been a part of various other safety committees of aviation regulator DGCA.
As the investigators begin probe into the accident, another aviation expert referred to the "widely recognised Swiss Cheese" model while talking about possible reasons for the crash that included breaking apart of the plane's fuselage.
"Any aeroplane accident that happens is never dependent on a single factor. Top air accident investigation teams across the world believe in the Swiss Cheese model. It says that only when the holes of all the slices of Swiss cheese get aligned, then only an accident happens," the expert said on condition of anonymity.
"It is just a metaphor. The Swiss cheese has lot of holes. If you put slices of Swiss cheese in a string and spin them, there will be one in a million times that all the holes would be aligned. That will be a precursor to an accident," he explained.
The expert said the reasons for the crash could include environmental factor, human factor, technical factor, health of the plane, administrative factor and external factor like what the air traffic controller is telling the pilots.
He said a sudden gust of wind leading to a wrong decision by the pilots, condition of the aircraft, wrong signalling by the instrument landing system or pure human error could be some of the reasons for the crash.
"It can be a multiple reasons. We cannot speculate. Wind speed could be a reason. When you are at low speed, you are susceptible to impact of the wind. One gust of wind can play havoc," he explained.
The runway 10 at the Kozhikode airport is approximately 2,700 metres long. The aircraft touched down approximately 1,000 metres from the beginning of runway 10 while landing, according to the AAI.
Captain S.S. Panesar, former director of flight safety and training at the Indian Airlines, said the pilot should have diverted immediately to one of the nearby airports like Trivandrum or Bengaluru after he did not succeed in its first attempt to land on runway 10 in bad weather condition, using the instrument landing system (ILS).
The ILS uses radio beams to give pilots vertical and horizontal guidance while landing the plane.
"The authorities have found the DFDR (digital flight data recorder) and CVR (cockpit voice recorder), but one thing will remain unanswered, that why didn't he divert?" Panesar asked.
The experts said the flight data recorder would give the investigators condition of the health of the aircraft, while the cockpit voice recorder will provide details of what the pilots were thinking and what they were going through before the crash.
Captain Deepak Sathe was the pilot-in-command and Captain Akhilesh Kumar was the first officer of the flight AIX1344.
According to the AAI, the visibility at Kozhikode airport when the flight landed was 2,000 metres.
The Kozhikode airport is a CAT-1 airport where flights can land with visibility of 801110 metres or more. At a CAT-IIIB airport, the runway visual range can be as low as 50 metres.
B737 is one of the most popular aircraft models of Boeing. According to the aircraft manufacturers' operations manual, a B737 plane can satisfactorily land or take off when the tailwinds are not more than 15 knots.
A former DGCA official told PTI that the accident could have been averted had the runway been extended some more during the last few years.
In 2017, the AAI had attempted to procure land to extend the runway, but it was not able to do so as the land acquisition was proving to be expensive and there was stiff resistance from locals, said the official.
Addressing the questions on runway 10, Civil Aviation Minister Hardeep Singh Puri said on Monday the airport is equipped with Runway End Safety Area (RESA) as per International Civil Aviation Organisation (ICAO).
Ten years back, an Air India Express aircraft overshot the table top runway at Mangalore airport, fell into a gorge and caught fire, resulting in loss of 158 lives.
Pointing to the similarities between the two accidents, Ranganathan said, "If the same error is done by the same airline (Air India Express), so what happened to safety audits and other checks that the DGCA has been doing for the last 10 years".
Panesar said there should be a judicial enquiry into the accident as it will allow aviation experts to file affidavits and ask pointed questions about the accident.