Sunday, September 26, 2021

The plane truth: Here’s why landing on a tabletop runway is so tricky

The Aircraft Accident Investigation Bureau’s recent report on the Air India Express Boeing 737-800 crash in Kozhikode a year earlier has blamed the tragedy on pilot error. The report’s findings have once again thrown the spotlight on the difficulty of landing on tabletop runways, especially in the rain.

Released on September 11, the report stated: “The probable cause of the accident was non-adherence to the standard operating procedure by the pilot flying the aircraft but the role of systemic failures as a contributory factor cannot be overlooked.”

India has five tabletop airports, at Shimla, Pakyong (Gangtok), Mangalore, Lengpui (Aizawl) and Kozhikode. Pilots add that, to a lesser extent, the Srinagar and Goa airports are also like tabletops. Domestic airlines such as IndiGo, SpiceJet and Go Air operate to these airports.

Shimla, the capital of Himachal Pradesh, has a very pronounced tabletop runway with deep gorges on both sides that is suitable only for light aircraft. Kozhikode and Mangalore, on the west coast, share similar weather, topography and operational constraints.

The AI Express aircraft that crashed in Kozhikode last year was on a Vande Bharat mission from Dubai. Before the Covid-19 outbreak, many international airlines also operated flights to Kozhikode airport.

A senior commander with a private airline who earlier flew with Jet Airways says that a tabletop airport is “a flat surface on which the airport is built, with the land sloping away on all sides around it.”

PP Singh, former Senior Vice President, JetLite, and currently Examiner, A-330, Nepal Airlines, adds that a tabletop airport is constructed on a raised plateau-like surface, where the runways are noticeably higher than the surrounding terrain. “There is a sheer drop on one or both sides of the runway and it has an aircraft-carrier-like appearance to the pilot of an approaching aircraft,” he says.

Given this challenging layout, pilots say it is very difficult to land at such airports. “The depth perception as a pilot approaches the tabletop runway is different from that of a runway on the plains,” explains a pilot.

“Initially the approach is over a lower area of land. As you get closer, the aircraft is descending and it comes over a much higher land area. This can be especially disconcerting in low-visibility conditions when there is fog or there are low lying clouds or heavy rain. The pilot has to be prepared for this change in the depth perception,” he says.

Pilots also point out that if you land short (before the runway) it can result in landing on terrain while overshooting can result in the aircraft going over the edge at the far end of the runway, both of which can be fatal. “The margin for error is very small,” a pilot adds.

Indeed, on May 22, 2010, Air India Express Flight 812 from Dubai to Mangalore, a Boeing 737-800, overshot the runway at the Mangalore airport before bursting into flames after plummeting down the hill. Of the 160 people on board, only eight survived.

Another pilot adds that to make an absolutely safe landing, the aircraft should touch down at the correct point, which is typically the first 3,000 feet of the runway. “If the aircraft keeps floating and touches down further with extra speed, the plane does not want to touch down, it wants to float, it wants to keep flying,” the pilot explains.

Hard as it is to land on a tabletop airport, inclement weather like fog and rain can make things worse both for landing and takeoff.

“Rain causes multiple problems for landing during the approach and then during the deceleration and stop after touchdown. On approach, the visibility is reduced below the reported value because of water on the windshield. Also, the water on the windshield causes a refraction error causing the runway to appear lower on the windshield. Depending on other factors, the magnitude of this error can be up to 5 degrees. This means a runway or terrain feature half a mile away can look up to 250 feet lower than it actually is,” Singh says.

There was light rain as AI Express 1344 tried to land at Kozhikode airport on August 7 last year. Of the 184 passengers and six crew members on board, 21, including the pilot and co-pilot, died in the crash while the others miraculously survived.

Then there is also the issue of loss of runway friction due to water, which increases the distance required to stop the aircraft. “A ballpark figure for increased distance is 15 percent, but it can be much higher if there are rubber deposits or standing water on the runway. The same hazards apply during takeoff — an aborted takeoff from high speed becomes really critical during rain,” says Singh.

“Visual illusions induce corrective actions from pilots, which are inappropriate and lead to deviations from the intended path. Tabletop runways appear raised from the background and look closer and higher than they actually are to the pilot on approach,” Singh adds.

However, pilots are not given any specific training to operate on tabletop runways as optical illusions and preventive strategies are part of all pilot-training programmes, which are expected to help pilots operate on such runways. “Airlines also require special characteristics of the airport to be included in crew briefings before every flight, as part of the Threat and Error Management process,” says Singh.

Other pilots add that most airlines do provide guidance material on the challenges that could be faced operating to these airports. “Landing on the runway itself is not difficult; it’s the peculiarity of the terrain that the pilot has to be careful about,” says one pilot.

25/09/21 Ashwini Phadnis/Moneycontrol

To Read the News in full at Source, Click the Headline


Post a Comment