Challenges in landing Airplane on tabletop runways.

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This article is about landing aircraft on tabletop runways and challenges associated with it. We will take an example of recent accident happened in Kozhikode, India and try to understand difficulties in landing. This article tries to analyze necessary factors involved in landing on tablet

Recently, Air India Express airplane carrying 190 people crashed while landing at Kozhikode international airport in India. The plane overshot the runway and fell into 35 feet deep valley taking life of 18 people sitting in the plane including pilot and co-pilot. It is because the pilot turned off both the engines the massive body did not catch the fire, which saved the life of hundreds of people in the plane. This happened although Wing Commander Deepak Vasant Sathe (retired), a top-notch Indian Air Force pilot, was the captain of the aircraft. This incident shades a light on challenges in landing the aircraft on tabletop runways. We need to understand few technical terms to before analyzing such accidents.

First let us understand tabletop runway. Tabletop runway is built on a plateau or a hill having deep cliff on one or both the sides of the runway. This can be understood by the analogy in the name - tabletop. Imagine a plane landing on the table having a drop on both of its ends which is sometimes hundreds of feet. Not all tabletop runways built on mountains, some being built on islands surrounded by sea on both sides. Some airports might have short runways having an upward slope. This helps aircraft to stop within a short distance. It is not possible to completely stop high speed aircraft in short distance as it carries large momentum. So, on such runways there is very little margin of error while landing an aircraft. That is why these runways pose challenges to even highly skilled and experienced pilots.

Most of the accidents happen either while landing or while takeoff of the plane. This is because pilot has very little time to react in these cases and even a slight mistake or ignorance can cause plane to crash. Lot of factors are involved while landing or taking off and it is necessary to understand the technique and process involved in these two phases. As we are analyzing plane crash while landing lets understand how landing takes place.

Every airport has air traffic controller (ATC), an electronic room at the airport, which handles take off and landings of all planes for that airport. Any plane ready for landing first contacts ATC of that airport. ATC assigns runway number it and makes sure the runway is available for landing. Once ATC sends go ahead signal for the landing next phase is to align the aircraft with runway. Pilot needs to maintain required height and align the aircraft with the center of the runway. It is also necessary to have a specific angle with the horizontal. To help the pilot for achieving required angle with horizontal and vertical all airports have Instrument Landing System.  These are microwave antennas installed at the start of the runway which emit specific frequencies. The transponder in the aircraft receives these signals, decodes it and calculates current position of the aircraft which is shown in the display installed in the cockpit. Thus, ILS helps pilot to take accurate position for landing. Once this is done pilot has to reduce speed and height maintaining the same position to touch runway at specific spot. 

Airport runway has specific markings which have specific meaning. Pilots see these markings from the plane and try to land plane accordingly. Here are some important markings and their significance:

  • Runway Centerline Markings: The centerline of a runway provides alignment guidance for taking off and landing. It consists of a line of 120-foot stripes and 80-foot gaps.
  • Runway Side Stripe Marking: Runway side stripe markings are white markings outlining the edges of a runway.
  • Runway Threshold Bar: A threshold bar presents the beginning of the runway available for landing if the threshold has been relocated or displaced. This bar is 10 feet wide and extends across the runway’s width.
  • Runway Touchdown Zone Markers: These markings pinpoint the touchdown for landing operations and are coded to provide distance information. These markings are grouped into one, two and three rectangular bars arranged in pairs about the centerline.
  • Runway Aiming Point Marking: The aiming point marking is used for a landing airplane. There are two rectangular markings with a large white stripe on either side runway centerline about 1,000 feet from the landing threshold.

These markings are visible in clear day time and white lights are used in the night to indicate safe landing points. However, it is very difficult for a pilot to spot these markings cloudy weather conditions.

Following figure shows markings on the runway.

 

Now we know required terms to analyze the challenges in landing on tabletop runway. So lets find out these challenges and some remedies to avoid similar accidents.

Plane must touch the ground at required position. Slight mistake may cause overshooting which means landing far away from the specified position. This makes impossible to stop the plane before the runway ends causing plane to crash in a valley after the runway. If plane overshoots pilot may decide to take off again instead of stopping the plane on the ground. This is called as go around. This is possible if plane is high enough to skip the landing and try another time. However, if it close to ground It requires large engine thrust to take off and fly again. If flight fail to take off properly it is going to make situation worse.  Sometimes flight engines thump the ground and may stop working or catch the fire. So, it is important to know much before if plane is going to overshoot. Too many go arounds create excessive pressure on pilot and this frustration force him/her to land the plane.

Bad weather conditions and fast flowing wind cause lot of trouble while decreasing height and speed of aircraft. Wind plays important role while landing. Heavy flowing wind pushes aircraft in wind direction. Direction of wind and speed makes difficult to align and land the plane correctly. If wind is in the same direction as that of plane it will push aircraft forward. In such situation plane may overshot the runway. Cloudy weather makes runway invisible and then pilot must take an accurate guess.

Due to the construction of the runway and its angle with horizon there can be an optical illusion. Runway might seem closer than it is, often misjudging the remaining length of the runway and overshooting. Raining makes runway slippery thus required friction cannot be generated to stop the plane. So, in such cases even landing is at correct place it becomes difficult to stop the plane before the runway ends. And we can imagine what might happen if plane overshoot the runway. Pilot has very little time to react in such situation and a panic may cause more errors even by professional pilots.

Sometimes airlines put pressure on pilot for smooth landing. This can be to provide comfort for passengers and there by increasing reputation of the airline. But this creates extra pressure on pilot in addition to bad weather conditions, slippery runways, fatigue due to long duration flight and dangerous construction of runways. Trying to land plane smoothly, pilot cannot reduce height and speed as expected as it causes plane vibrations. Thus, this pressure creates chances of overshooting.

 

How can we avoid these accidents?

  • It is necessary to identify dangerous airports and avoid landing or takeoff of large commercial planes. Airforce planes can use such airports as they have ejection seat and they carry a smaller number of people.
  • We must make tabletop runways sufficiently long so that there is sufficient margin to stop the plane even in case of overshooting.
  • Downward slope on the runway gives extra push to the plane. Thus at least tabletop runways must be straight and perfectly horizontal to ground surface.
  • Safe landing is important than smooth landing. So, pilots must not be pressurized for smooth landing.
  • Long duration flights create fatigue. Pilots should take adequate rest and sleep during long duration flights because our senses do not work efficiently in case of fatigue and frustration.
  • An autopilot system in aircraft can be capable of many very time intensive tasks, helping the pilot focus on the overall status of the aircraft and flight. Pilot must not depend totally on autopilot systems. Any misfunctioning can happen in machines thus it not good to handover the complete process to automatic systems.
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