August 12, 2020

 The crash of Air India Express (IX) flight IX-1344 at Calicut International Airport (CCJ) in India on August 7 was one of the deadliest runway excursion incidents in the past decade. Runway excursions – incidents in which a plane runs off the side or end of a runway – are some of the most common incidents in commercial aviation, and the vast majority of these incidents do not result in any serious injuries to passengers. The consequences of a runway excursion depend on the speed at which an aircraft leaves the runway, and more importantly, the distance between the runway and any nearby obstacles, such as structures, trees, steep terrain, or bodies of water. 


Risk Factors for Runway Excursions

The primary causes of runway excursions are weather factors and pilot errors. A 2008 study by the Australian Transport Safety Bureau (ATSB) found that weather played a role in over three quarters of runway excursion accidents involving commercial airliners. Not only does poor weather often decrease an airliner’s braking capabilities due to rain, snow, or ice on the runway, but clouds and high winds can cause an airliner to land too far down the runway to stop safely. The same ATSB study found that a majority of runway excursions involved poor decisions or piloting skills from flight crews.

The outcome of a runway excursion accident depends largely on whether the aircraft strikes any obstacles after leaving the runway. Most aircraft that run off of runways end up on flat, obstacle-free ground next to or slightly beyond the runway; such incidents pose little danger to those onboard the aircraft. Runway excursions are significantly more dangerous at airports that have buildings, trees, bodies of water, or steep terrain close to the runway. Such airports tend to be older and located close to city centers or in hilly areas. These complexes often operate under grandfather clauses that exempt them from modern regulations requiring flat obstacle-free zones near runways.

The crash of Flight IX-1344 highlighted the danger of so-called “tabletop runways,” which have steep drop-offs near on the sides and end of the runway. Runway excursions at these airports often become major accidents, and the two deadliest runway excursion accidents in the past 20 years occurred at airports with such setups. The deadliest of these accidents was the 2007 crash of a TAM Airlines (JJ) aircraft at Congonhas Airport (CGH) in Sao Paulo, Brazil, which ran off the side of the runway while landing in a rainstorm and crashed into a warehouse below, killing all 187 people onboard. The other involved another Air India Express flight in 2010 that ran off the end of the tabletop runway at Mangalore International Airport (IXE) while landing, killing 158 of the 166 people onboard. 


Frequency of Runway Excursions

Data on the frequency of runway excursions varies considerably due to inconsistent reporting and varying definitions over what constitutes a runway excursion, but most sources agree they are among the most common types of safety incidents involving commercial airliners. A 2010 study of data from 1980-2008 by the Dutch NLR Air Transport Safety Institute found that there were approximately 60 runway excursions involving commercial flights per year, and a search of The Aviation Herald’s database found broadly similar results.

The vast majority of runway excursions do not cause fatalities. According to data from the Aviation Safety Network, there have been seven fatal runway excursions on commercial passenger flights since the start of 2011. Between 2006 and 2010, however, there were 17 fatal runway excursions involving commercial passenger flights, plus three additional that killed individuals on the ground.

Runway excursions are more common business jet and small commuter aircraft than among commercial airliners. There are likely several reasons for this trend, including the lower pilot experience and qualifications required to operate business jets and commuter aircraft, and the fact that the smaller aircraft often fly into smaller airports with shorter and narrower runways than those used by commercial airliners. While individual runway excursions are generally not a cause to worry about an airline or charter operator’s safety standards, repeated runway excursions in a short time period can be an indicator of poor piloting standards at an operator.


Improvements in Runway Excursion Safety

The decrease in fatal runway excursion accidents since 2010 has been driven by a number of factors, including improved pilot training and improvements in airport safety. Over the past decade, pilot training has placed an increased emphasis on executing more controlled approaches for landing (known as stabilized approaches), and on aborting approaches that are more likely to result in runway excursions while landing. The past decade has also seen pilots become more familiar with the increasingly automated systems on modern airliners; two of the worst runway excursions between 2006 and 2010 were caused by pilots misunderstanding the automated braking, spoiler, and reverse thrust systems on their aircraft.

Airports have implemented numerous safety upgrades over the past 15 years to reduce the severity of runway excursions. The most notable innovation has been Engineered Materials Arresting Systems (EMAS), which are beds of crushable concrete installed at the end of runways to stop aircraft that run past the length of the runway. The US Federal Aviation Administration (FAA) has strongly advocated the use of EMAS at airports that do not have adequate runoff space at the end of runways, and as a result, the systems have been installed at many US airports. According to the FAA, EMAS beds have safely stopped 15 aircraft since 1999, including a Boeing 737 carrying US vice-presidential candidate Mike Pence at New York’s LaGuardia Airport (LGA) in October 2016. Several airports that have had serious runway excursion accidents have been replaced or significantly upgraded in the past decade.


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