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Much Ado About Table Tops

Issue: 06-2010By Air Marshal (Retd) B.K. Pandey

No runway length would be adequate if the crew of the aircraft fails to land the aircraft at the correct speed in the prescribed touchdown zone

As it usually happens, there is widespread speculation about the cause of the disastrous end to Air India Flight IX 812 on May 22, 2010 while landing at dawn at the Mangalore International Airport. The precise cause, however, will only be known with a reasonable degree of certainty only after data from the cockpit voice recorder and the digital flight data recorder also referred to as the Black Box, is studied and analysed by the investigating agency. Meanwhile, there is speculation that the accident occurred because the ‘table top’ runway at Mangalore International Airport is not long enough for safe commercial operations. This view which appears to be a legacy of the past when the old 5,330 feet runway was in use seems to have been reinforced by statements emanating from two sources in the political leadership. The first was by Praful Patel, the Union Civil Aviation Minister, about plans to extend the runway by 1,000 feet and the second by S.M. Krishna, the Union Minister for External Affairs, who after the accident said, “It was known that the Mangalore airport has a very tricky runway and the skills of the pilot would be put to the maximum test while landing there. Our worst fears have now come true.”

While it is a fact that the new runway 24/06 at Mangalore airport is only 8,038 feet in length, somewhat less than the standard length of 9,000 feet, it is much longer than the old runway 27/09 which was only 5,330 feet. The new runway was built in 2006 and is quite adequate for a medium size commercial aircraft such as the Boeing 737-800 NG or the Airbus 320 and as such the airport is no longer in the Special Category. As per the operating manual of Boeing 737-800 NG, the type involved in the crash in question, when landing at the upper permissible limit of the landing weight in calm wind conditions prevailing at sea level under International Standard Atmospheric (ISA) conditions and maximum braking available, the stopping distance would be just under 4,500 feet. This distance is measured from the threshold of the runway and is conditional to the fact that the aircraft while approaching to land, crosses the threshold of the runway at a height of 50 feet or less. With the application of full reverse thrust on both engines, the stopping distance would be considerably lower than 4500 feet. However, in case the touchdown speed of the aircraft is higher than that prescribed for a given landing weight, the stopping distance would be correspondingly higher.