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Explained | What can cause an aircraft to fly into terrain?

Wreckage of the crashed IAF Mi-17V5 helicopter, in Coonoor, Tamil Nadu on December 8, 2021. CDS Gen. Bipin Rawat accompanied by his wife Madhulika Rawat, his staff and other officials were on board.
Suresh SeshadriJanuary 23, 2022 03:45 IST
Updated: January 24, 2022 11:19 IST

How frequent are such mishaps? What type of technology and pilot training are required to avert these accidents?

The story so far: Earlier this month, the Indian Air Force announced that the preliminary findings of a tri-services inquiry into the Mi-17 V5 helicopter crash that killed Chief of Defence Staff (CDS) Gen. Bipin Rawat and 13 others in December had established that an “unexpected change” in weather conditions had led to the spatial disorientation of the aircraft’s pilot resulting in Controlled Flight into Terrain (CFIT) .

What is Controlled Flight into Terrain?

The International Air Transport Association (IATA), the airline industry’s trade association that supports aviation with global standards including for airline safety and security, defines a Controlled Flight into Terrain incident as an accident in which there is a collision with terrain, water, or obstacle during the course of a flight, without indication of loss of control. IATA stresses that the critical distinction in these incidents versus other types of aviation accidents is the fact that the aircraft remains under the control of the flight crew till the occurrence of the incident.

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How does a CFIT incident occur?

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An IATA analysis of CFIT accidents involving commercial flights between 2008-2017 established several factors that could contribute including: ‘Latent Conditions or conditions present in the system before the accident and triggered by various possible factors; Environmental Threats where an event or error occurs outside the influence of the flight crew, but which requires crew attention and management if safety margins are to be maintained; Flight Crew Errors where an observed flight crew deviation from organisational expectations or crew intentions occurs; and Undesired Aircraft States where a flight-crew-induced aircraft state clearly compromises safety of the aircraft.The study also found that the approach-cum-landing phase of an aircraft’s flight accounted for two-thirds of all CFIT accidents and contributed to 62% of fatal CFIT incidents.

What exactly happened in the case of Gen. Rawat’s flight?

Specifically, in the case of the military helicopter that crashed while flying over the Nilgiris to its destination at the Defence Services Staff College’s helipad in Wellington, the court of inquiry found that an unexpected change in weather conditions in the valley resulted in the aircraft flying into clouds that in turn caused the helicopter’s pilot to experience sudden spatial disorientation —a condition where the pilot loses the ability to correctly interpret aircraft attitude, altitude or airspeed in relation to the Earth or other points of reference— and made him fly into terrain.

How often do CFIT accidents occur?

While the breakdown of such incidents concerning military aircraft is hard to find in the public domain, the IATA ‘Accident Analysis Report’ for the 2008-2017 period found that while CFIT incidents accounted for 6% of 837 commercial aviation accidents recorded in the IATA Accident Database, disproportionately CFIT was the second most frequent category of fatal accidents, representing 42 fatal accidents or almost 28% of total fatal accidents.

 

The only category of accidents with a higher level of fatalities was Loss of Control In-flight (LOC-I).

Also, CFIT accidents tend to be severe in terms of the number of fatalities and the extent of damage to the airframe. Forty six out of the 47 CFIT accidents in the IATA study resulted in a hull loss —in other words the aircraft was a complete write-off.

For the majority of CFIT incidents relating to commercial flights, 70% involved turboprop aircraft, with planes with jet engines only accounting for 30% of such accidents.

 

How can such incidents be avoided?

A combination of the use of technology and appropriate and adequate pilot training, including in simulators, can help minimise/avoid CFIT incidents. Particularly, installation of Ground Proximity Warning System (GPWS) / Terrain Awareness and Warning System (TAWS) in aircraft help generate the requisite alerts to the flight crew and if the pilots are adequately trained to respond to these alerts, maintain situational awareness and make the right interventions, CFIT accidents can be mostly avoided.

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