IndiGo plane avoids crash by 30 seconds, leaves many lessons in its wake
It is recommended that operators increase training on maintaining situational awareness at all times
An IndiGo ATR-72 taking off from the Shillong airport on February 27, 2021, was seconds away from disaster when the Enhanced Ground Proximity Warning System (EGPWS) alerted the crew that the flight path that they had chosen would end up in the plane flying into a hill ahead.
The crew were alerted approximately 30 seconds before impact with the mountains by an automated visual and audio alert "Terrain Ahead Pull Up". The crew reacted instinctively according to well-rehearsed training procedures to steer the aircraft away from danger. Everyone is prone to errors and there are warnings too but it is only a well-trained crew that is able to react in a timely manner to prove the effectiveness of training.
‘Saves’: Accidents avoided (Source: International Civil Aviation Organisation)
The industry has recorded a number of ‘saves’ where the EGPWS alerted the crew just in time to avoid an accident; some of these events were sufficiently serious to require national authority investigations, reports of which are expected to be published.
Representational image of an IndiGo ATR-72 plane. Image courtesy: Wikimedia Commons/Dylan Agbagni
Other ‘saves’ have been investigated by operators and manufacturers to gain an understanding of how the aircraft became exposed to a terrain or obstacle hazard and to identify the circumstances that prevented the crew from detecting the threats earlier.
A particular group of incidents, those involving premature final descent for landing, has been used in these investigations to seek answers as to both the nature of the threats and the circumstances of crew behaviour.
The IndiGo plane was seconds away from disaster. Image courtesy: Captain Amit Singh
There were no common features involving the operators, size of the airlines or locations. However, although the data are from a very small sample, there were some correlation with well-documented factors in previous Controlled Flight Into Terrain (CFIT) accidents (special report Killers in Aviation – Flight Safety Foundation Digest November-December 1998, January-February 1999).
Why does CFIT occur?
It seems somewhat unbelievable that an aircraft capable of a safe flight can be flown into terrain, water, or any other obstacle while under the control of the pilot. While CFIT accidents are often the product of a chain of events, the investigation of CFIT accidents has identified the following:
- CFIT can occur during most phases of flight but is more common during the approach-and-landing phase.
- Non-precision approaches are associated with CFIT accidents.
- Inappropriate action by the flight crew has been cited as a contributing factor. This refers to the flight crew continuing descent below the Minimum Descent Altitude (MDA) or decision height without adequate visual reference.
- Lack of positional awareness, resulting in an accident.
- Failure in CRM (cross-check, communication, coordination, leadership etc.) has also been cited as a contributing factor.
- Pilots have either failed to respond or delayed their response to ground proximity warnings.
- Non-adherence to Standard Operating Procedures (SOPs).
- The use of early Ground Proximity Warning System (GPWS) equipment.
- Overall, when compared with the total number of accidents recorded in the accident database over a period, the likelihood of a CFIT accident is very low. However, when CFIT accidents did occur, 99% resulted in hull loss and 88% incurred fatalities.
Factors involved in CFIT accidents
(Source: IATA study)
Lack of awareness has been the top factor in CFIT accidents according to an International Air Transport Association (IATA) study. Despite visual representation of the terrain available to the crew, accidents do happen. This is due to human factors and must be looked into during investigations to spread awareness.
CFIT near misses offer operators the opportunity to learn and develop appropriate mitigations prior to an accident, and the best medium for gathering this data is Flight Data Analysis (FDA).
It is recommended that operators implement a comprehensive FDA programme, which specifically facilitates the detection and analysis of CFIT precursors, and use the derived knowledge to develop mitigations and inform pilot training programmes.
Situational awareness was found to be deficient in all of the accidents analysed. It is recommended that operators increase training on maintaining situational awareness at all times, especially when close to the ground, and provide pilots with appropriate language and procedures to communicate and respond to positional concerns without delay.
(This article first appeared in safetymatters.co.in)