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The Hindu Explains | What is a ‘tabletop airport’ and how many are there in India?

The tabletop runway of the Calicut International Airport in 2017.

The tabletop runway of the Calicut International Airport in 2017.   | Photo Credit: S. Ramesh Kurup

The story so far: On August 7, a Boeing 737 of Air India Express (the low cost subsidiary of national carrier Air India) on a special ‘Vande Bharat’ repatriation flight from Dubai to Kozhikode overshot the runway. There were ‘174 passengers, 10 infants, 2 pilots and 4 cabin crew on board’. In what was its second attempt, flight IX-1344 touched down on runway 10 of Calicut International Airport at 7.40 p.m., went past the runway end and safety area, and fell into a valley. The fuselage split in the impact. Both pilots lost their lives; there were casualties and injuries of varying degrees among passengers. There was no fire on board. The Digital Flight Data Recorder and Cockpit Voice Recorder have been recovered. The accident has once again turned the spotlight on operations to what are called ‘tabletop airports’ in India.

What is a ‘tabletop airport’ and how many are there in India?

As the name suggests, it is an airport located and built on top of a plateau or hilly surface, with one or both ends of the runway overlooking a drop. The airports in the country which would count as “tabletops”, are namely Lengpui (Mizoram), Shimla and Kullu (Himachal Pradesh), Pakyong (Sikkim), Mangaluru (Karnataka), Kozhikode and Kannur (both Kerala).

Kozhikode plane crash | Death toll hits 18, probe begins

A retired aviation official says there is no such term as a ‘tabletop airport’ in any International Civil Aviation Organisation (ICAO) technical document. But India’s statutory aviation body, the Directorate General of Civil Aviation (DGCA), refers to these airports in this manner by way of highlighting safety measures during operations to these runways. The official adds that there are not many differences between a ‘normal’ airport and a ‘tabletop’ airport.

Why are these airports drawing attention now?

While there have been some aviation incidents at these airports, it was the accident in Mangaluru on May 22, 2010, that highlighted operational risks. Here, an Air India Express flight again, from Dubai to Mangaluru, overran the runway while landing on runway 24. Flight IX-812 hit an antenna and then went down a steep embankment after which there was a fire. Of the 160 passengers and 6 crew, 158 lost their lives. The case focused attention on the nature of operations to such airports, especially their shorter runways.

Kozhikode has two runways of 2,700 metres in length. It was 2,860 metres but ‘shortened’ to accommodate a safety feature called RESA, or Runway End Safety Area (of 240 metres), which is a means “to limit the consequences when there is an aircraft overrun during landing, a rejected take-off, or even undershoots the landing area”. In “tabletop” airport operations, the ICAO says a RESA of 90 metres is mandatory, while 240 metres is recommendatory. The runways are Instrument Landing System (ILS) CAT 1 enabled and the airport has a range of visual aids which include simple approach lighting. In addition, all obstacles are lit. Both runways have Required Navigation Performance approach.

Also read | 2011 report flagged unsafe conditions at Calicut airport

The retired official says there have been Code E aircraft (based on wingspan) operations to Kozhikode airport. Kannur and Mangaluru too have had widebody aircraft operations. The largest aircraft at Kozhikode (and at any tabletop airport so far) has been Air India’s 423-seater Boeing ‘jumbo’ 747, operating on the Kozhikode-Jeddah sector.

What were the recommendations made after the Mangaluru crash?

In its report on the crash, the court of Air Marshal B.N. Gokhale, former Vice-Chief of Air Staff, Indian Air Force (and its team of aviation expert assessors) made a series of recommendations in a 191-page document of October 2010. These were addressed to the airline operator (Air India and Air India Express). To the Airports Authority of India, it pointed out issues like “avoidance of the downward slope in the overshoot area particularly on ‘tabletop’ runways; the need for a ground arresting system for aircraft — such a facility is maintained at almost all airfields of the Indian Air Force’; a visual reference system to alert the pilot (while landing) of the remaining distance to be covered; location of the ATC tower, approach and area radars; the role of the Rescue and Fire Fighting service, aerodrome risk assessment and, finally, recommendations for the DGCA.

Kozhikode plane crash | Several safety recommendations were heeded, says DGCA Chief Arun Kumar

Is there any ICAO document on operations?

The retired official says there is an ICAO document 9981 for airports, which also serves as a guideline for compatibility study of the operation of larger aircraft in a comparatively smaller aerodrome. The issue of growth versus aviation services is a worldwide issue requiring the development of small aerodromes for the use of bigger aircraft in a safe manner, especially as demand for air services grows from existing airports. In this document, the elements to be assessed include aerodrome infrastructure and its ground handling capabilities, and aeroplane characteristics. Each element is assessed technically to see whether these are compatible for new types of aircraft proposed to be operated in such aerodromes. Thereafter, a proper safety assessment is done to assess the risk associated with the operation of higher category of aircraft. Risk mitigation measures are suggested in order to bring those risks within “tolerable limits”. Such a compatibility study and safety assessment report will be scrutinised by the regulatory aviation authorities and if found satisfactory, the no objection certificate for operation of such higher category aircraft is issued.

When a need was felt to upgrade services at Kozhikode, the airport undertook a runway recarpeting and strengthening exercise between 2015 and 2017.

Could safety measures be better in terms of the ground infrastructure?

While RESA is in vogue, the term EMAS has been tossed up, which is mandatory at all international airports in the United States. Called Engineered Materials Arrestor/Arresting System, it is made of engineered lightweight and crushable cellular cement/concrete.

Used at the runway ends, it acts as a safety barrier and successfully stops an aircraft overrun. Its retarding effect increases as one moves away from the runway edge. In demonstrations in the West, it ensured good aircraft safety. It must be noted that these are laid in easily replaceable blocks in the overrun area. The material is engineered specifically for the airport it is to be used in, says the retired official. It is said to be ideal for use in ‘tabletop’ airports. About 75m of EMAS can serve the purpose of 240m of RESA without causing any damage to the aircraft.

How are operations from a pilot’s point of view?

A senior airline commander, who is also an instructor and check pilot, says that in reality, there is no specific training that can be given for ‘table top’ runways. However, airlines conduct route checks for short runways. He says that one needs to understand that the landing technique and precautions taken are the same for all runways except that there is no scope for error on short and/or ‘tabletop’ runways. As aircraft accident data show, “runway overshoots” (excursion) occur as often on non-‘tabletop’ runways. But in such cases, the aircraft, for obvious reasons, has a much better probability of surviving. However, an overrun by even a few metres can turn catastrophic for ‘tabletop’ runway landings.

During pilot training, the emphasis is on aiming for 1,000 ft from the beginning of the runway and landing within the touchdown zone. Pilots are also trained to execute a go around if they do not make contact within the touchdown zone. Now, the senior commander says, there is a lot of emphasis on this aspect and pilots are asked to have this uppermost in mind while operating on a short or ‘tabletop’ runway . Further, Crew Resource Management is a mandatory training for all pilots following the recommendations made after the Mangaluru crash, which include classroom and simulator training. Here, the senior commander says, emphasis is placed on training the copilot to ask the commander to initiate a go around in case of an unstable approach or if the aircraft has not touched down within touchdown zone. He or she is even trained to take over as a last ditch measure in case the commander does not heed the copilot’s safety advice to initiate a go around. Other than this, classroom training and simulator training are provided to explain various types of optical illusions including those caused by ‘tabletop’ runways. There is a lot of training done on the simulator for landing in low visibility, heavy rain and winds. This happens during initial induction training and every six months thereafter. As the monsoon is a major factor in Indian aviation, monsoon training is given during initial command training before release. The senior commander adds that certain restrictions are placed before releasing the pilot in command for monsoon operations. Such comprehensive training helps in any landing on any runway and can especially be a life saver in ‘tabletop’ operations. The DGCA has mandated a Monsoon Minimum Equipment List as far as aircraft operations are concerned. Here it is mandatory that aircraft devices used in braking or slowing such as brakes and reversers are completely operational.

What is the role of the air traffic control?

The ATC only has jurisdiction to provide the pilots with weather conditions including visibility, rain and winds. The minimum visibility is already prescribed, says the senior commander. The ATC will not give clearance to commence approach if visibility is below this minima, but if the visibility meets the requirements then the ATC cannot stop the pilot. The pilot commences approach when visibility is within minima and descends towards the runway to land. At a point called Decision Height, or DH (normally around 200 ft) in case of ILS, and at a point called Minimum Descent Altitude, or MDA, in case of a non precision approach, the pilot must be aware of the runway environment in order to make a safe landing. If he has not, then he has to initiate a go around, circle and return for another attempt at landing. Many a time, the runway cannot be seen even when reported visibility conditions meet the requirements as the conditions measurable on ground by the meteorological department are not the same as the instantaneous condition on the approach path. Only a pilot can observe this.

So essentially, after a point, the ATC has a limited role, says the senior commander.

If the declared visibility meets the prescribed minima, there is nothing wrong in the pilot attempting an approach. But trying to come in below DH and MDA, if the runway is still not visible is illegal, says the senior commander. No pilot does that, he adds.

One needs to understand, he says, that in heavy rain, even if the runway is visible in time, sometimes due to sudden burst of heavy rain during the final touchdown, it is very difficult for the flight crew to fine tune their judgement of flare height. This may even cause a pilot to land beyond the touchdown zone. Finally, he says, all airline companies ask their pilots to divert in case of a thunderstorm and in their opinion if the weather is unsafe even if it meets the minima. But if there is only rain and no thunderstorm seen on aircraft radar then a pilot will attempt an approach and take decision at DH/MDA.

What must Indian aviation do?

Aviation safety expert Captain Mohan Ranganathan says India needs to move away from the culture where, after every fatal incident, officials say runways will conform to ICAO standards, the investigation will identify the accident cause, and steps will be taken to rectify the deficiencies. He says if the government is serious it needs to declare Kozhikode as a Code 3C airport, for only narrow body aircraft; ban landings on runway 10 during the monsoons; ensure that all runway condition standards are enforced; ensure approach and landing accident training for pilots is enforced strictly and, finally, be transparent and safety-oriented and not look at commercial interests.

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