IndiGo ATR-72 taking off from Shillong airport 0n 27th Feb 2021was seconds away from disaster when the enhanced ground proximity warning system (EGPWS) alerted the crew that the flight path that they had chosen to fly would end up flying into a hill ahead.
The crew were alerted approx. 30 seconds before impact with mountains, by an automated visual and audio alert “TERRAIN AHEAD PULL UP”. The crew reacted instinctively as per well rehearsed training procedures to steer the aircraft away from danger. Everyone is prone to errors and there are warnings too but it is a well trained crew who is able to react in a timely manner to prove the effectiveness of training.
‘Saves’ – An accident avoided.(Source ICAO)
The industry has recorded a number of ‘saves’ where EGPWS provided a timely alert to the crew to avoid an accident; some of these events were sufficiently serious that national authority investigations were required, reports of these are expected to be published. 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, is used in this report to seek answers as to both the nature of the threats and the circumstances of the crew’s behaviour.
There were no common features involving the same operator, size of airline, or world location. However, although the data is from a very small sample, there was some correlation with the well documented factors in previous controlled flight into terrain (CFIT) accidents (Special Report ‘Killers in Aviation’ – Flight Safety Foundation Digest Nov-Dec 98 Jan-Feb 99).
Why does CFIT occur?
It seems somewhat unbelievable that an aircraft capable of a safe flight can be flown into terrain, water, or obstacle while under the control of the pilot. While CFIT accidents are often the product of a chain of events, the investigation of these nine 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 were associated with CFIT accidents.
- Inappropriate action by the flight crew was 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.) was cited as a contributingfactor.
- 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 the period, the likelihood of a CFIT accident occurring is very low. However, when CFIT accidents did occur, 99% resulted in hull loss and 88% incurred fatalities.
Factors involved in CFIT
Factors involved in CFIT accidents (Source IATA study)Lack of awareness is the top factor in the past accidents as per IATA study. Despite visual representation of the terrain available to the crew, accidents so happen. This is due to human factors and must be looked into during investigations in order 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 program which specifically facilitates the detection and analysis of CFIT precursors, and to use the derived knowledge to develop mitigations and inform pilot training programs.Situational awareness was found to be deficient in all of the accidents analyzed. 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.