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A combination mechanical failure and pilot error may have caused the Alliance aircraft's mysterious dive to disaster

By Vijay Jung Thapa and Rohit Saran with Sayantan Chakravarthy in Patna

Bharat Rungta was the last person to board the Alliance Air flight CD 7412 in Calcutta on the morning of July 17. The chartered accountant remembers the morning as a series of uncharacteristic events. Though he's the kind of person who reaches the airport way ahead of the departure time, that day he had to be woken up by his parents. Inside the aircraft, he grudgingly accepted a window seat on the very last row even though he usually likes to sit in the front. Though he usually tries to get some work done during the flight, this time however he just asked for a blanket and curled up to sleep. He remembers nothing else about the 40-minute flight except the last 10 seconds. In his words: "Suddenly there was this huge sound. Then the aircraft went into a series of jerky manoeuvres ... and then we hit the ground with a huge crash." The impact of the crash not only broke the aircraft into three pieces but threw Rungta clear. He was found lying on a fiery bed of mangled debris and charred bodies. Miraculously, he and six other passengers were still alive.

But 51 others aboard CD 7412 died a violent, instantaneous death when the Boeing 737 aircraft, on the home stretch to the runway, suddenly veered to the left. Like an errant missile, it first grazed a single-storey building, then bent a tall telegraph pole, sliced through four peepal trees before tonnes of flaming metal exploded on a cluster of government houses in the Gardani Bagh suburb of Patna. The impact created a huge fireball on the ground, killing five more people and injuring four others. Rambilas Ram, a former inspector-general of police, was standing on his terrace from where one can see aircraft approaching the airport. He was waiting for CD 7412 because it was bringing his daughter Pallavi home. She never made it. "I heard a huge sound and then saw flames leaping into the sky. I knew what had happened."

Minutes later, a clumsy rescue mission got underway and the familiar holes in the crisis management of our airports were revealed all over again. Air traffic controllers alerted the single airport fire brigade which rushed out in search of the crash site. It took the fire brigade 25 minutes to reach the site and just a few minutes to exhaust all the water it had. Then everybody, including those injured and trapped in the debris, waited for ambulances to arrive from the city. That took another half an hour. Remembers Amarendra Mishra, a survivor: "I was in the bathroom. There was a flash of light and then the roof collapsed." It took an hour to extricate him.

Unsurprisingly, there is no dearth of theories on what could have caused the crash. In the next few weeks a lot of these theories are going to bite the dust. What the inquiries are going to rely on are the facts. Which are:

• Just eight minutes before the crash, one of the pilots radios in to Air Traffic Control (ATC) that the aircraft is hovering at 4,000 ft, 13 km from the runway.

• At 7.30 a.m., the pilot of the aircraft, which is now only 1.3 km away, radios in to say that its altitude is too much and seeks permission for a 360 degree orbit that will help lose height (aircraft in a descending orbit lose 300 ft every mile).

• At 7.34 a.m. the aircraft finishes the orbit, is now presumably at the required height of 1,700 ft and is turning to align itself with the runway when it wobbles and loses height suddenly.

• It drops at 80 m a second, grazing a building at 300 kmph, then hits the ground with about 2,000 litres of fuel in its tank that turns it into an inferno.

The most apparent of cause of the crash seems to be the old age of the CD 7412. At 20 years it was the oldest plane in the Alliance fleet. Alliance pilots allege that the aircraft had been plagued with engine malfunctioning, something that the airline denies. However, engine trouble is an unlikely cause of the crash since the pilots didn't report any snag throughout the flight. The same aircraft had another accident 14 years ago in Tiruchirapalli where one of its wings had been damaged. But age itself isn't a safety hazard. Close to 500 20-year-old Boeing 737 aircraft (the oldest being 28) are flying for various airlines. What's more important is regular maintenance. The aircraft had recently gone through an overhaul in January and its airworthiness certificate was renewed in March.

Another plausible reason could be the "runaway rudder" -- a known malfunction in Boeing 737-200 aircraft. After a spate of accidents, the US Federal Aviation Administration identified a fault in the hydraulic system that powers the rudder. Apparently, the rudder (used for correcting the aircraft drift) either gets stuck or works the opposite way. Though Boeing had modified the rudder in this particular aircraft, experts believe a problem still persists. The fact that the aircraft took a mysterious dive while coming out of its turn could indicate a runaway rudder.

Pilot error is the most obvious possibility. But both pilots -- Captain M.S. Sohanpal and Captain A.S. Bagga -- had extensive experience. They had over 4,000 flying hours of experience and were veterans in flying the Boeing 737. True, they did not opt for the instrument landing system that is available in Patna, choosing instead to use the visual approach slope indicator (VASI) method -- basically a set of lights on the runway that help the pilot align the aircraft and ensure he is descending at the right angle. But experts say the decision to opt for VASI isn't unusual or incorrect considering visibility was good. As Captain R. Dhruv, secretary, Indian Commercial Pilots Association (ICPA), says, "All the other parties are trying hard to shift the blame out of their backyard. Only the pilot is dead, it's easy to blame him."

Some experts have even raised the possibility of a freak weather pattern called windshear -- known to occur during the monsoons -- where two strong wind currents work against each other. When an aircraft gets caught between these two currents, a vacuum is created and the aircraft gets sucked into it. Though survivors do report the aircraft "wobbling" and "lurching" -- conditions that lend credibility to the windshear phenomenon -- most experts dismiss this theory. The reason: the weather that day was calm with wind speeds on the ground not exceeding six knots. Besides, the pilots too did not report any unusual weather.

In all probability none of these probable causes would have crashed the CD 7412. Rather a combination of factors could be at work. The truth will come out once the digital flight data recorder -- which records 35 of the flight parameters -- and the cockpit voice recorder are decoded and the judicial commission gets underway. Like so many past inquiries into air disasters, the two inquiries instituted now -- a DGCA investigation and a more substantive court of inquiry -- may find that the reasons for the disasters lie with the Civil Aviation Ministry, the DGCA and beyond.

For instance, questions could be raised about the procrastination in fleet renewal. Even if not for the reasons of safety, for the sake of efficiency and economy, Indian Airlines (IA) should acquire new planes. The IA last purchased aircraft in 1994. Says Akbar Hameed Jung, secretary, civil aviation and a survivor of a 1993 aircrash in Delhi: "The airlines obviously needs new planes and we will go ahead with it irrespective of the disinvestment programme." The IA has been working on an ambitious plan to acquire 40-odd new aircraft in the next five years at the cost of Rs 9,000 crore. Only the plan has been on since April 1999 and there is no knowing when it will materialise. Especially now that privatisation process will slow the decision making.

Each day's delay in fleet renewal is weighing down the already over-burdened maintenance. The entire fleet of IA's 11 Airbus A-300 is more than 21 years old, more ancient than Alliance's 737 fleet. Admits H.S. Khola, DGCA: "As aircrafts become older, our checks become more frequent." Claims Jung: "We could compromise on punctuality, but never on safety." DGCA may, as they claim, have one of the most stringent test systems in the world. But then India also has one of the worst air safety records in the world.

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