Contribution of Unstabilised Approaches to Aircraft Accidents and Incidents

Description

The Flight Safety Foundation (FSF) established that unstabilised approaches were a causal factor in 66 % of 76 approach and landing accidents and incidents worldwide between 1984 and 1997.

It was found that many low and slow (low energy) approaches have resulted in controlled flight into terrain (Controlled Flight Into Terrain (CFIT)) because of inadequate vertical position awareness. Low energy approaches may also result in "loss-of-control" or "land-short" events.

High energy approaches have resulted in runway excursions and also have contributed to inadequate situational awareness in some of CFIT accidents.

It was found that a crew’s inability to control the aircraft to the desired flight parameters (airspeed, altitude, rate of descent) was a major factor in 45 % of 76 approach-and-landing accidents and serious incidents.

Flight-handling difficulties have occurred in situations which included rushing approaches, attempts to comply with demanding ATC clearances, adverse weather conditions and improper use of automation.

Consequences

Unstabilised approaches can be followed by:

  1. Runway excursions
  2. Landing short
  3. Controlled flight into terrain
  4. Hard landings
  5. Tail Strike

Contributory factors

Weather conditions or approach types which can increase the chances of an unstabilised approach are:

  1. wake turbulence
  2. strong winds
  3. low visibility
  4. heavy precipitation
  5. an approach with no visual references (e.g. night or Instrument Meteorological Conditions (IMC))
  6. visual approach
  7. circling approach

Aircraft Accidents and Incidents Related to Unstabilised Approach Listed on SKYbrary

On 4 October 2017, an Airbus A320 slightly overran the end of runway 22 at Surat during an early morning daylight landing. A temporarily displaced landing threshold meant the runway length was only 1,905 metres rather than the 2,905 metre full length. The aircraft remained on a paved surface and was undamaged. Its crew did not report the excursion which was only discovered when broken runway lighting was subsequently discovered. The Investigation found that the non-precision approach made was unstable and that a prolonged float in the subsequent flare meant that only 600 metres of runway remained ahead at touchdown.

On 2 September 2016, an ATR72-600 cleared to join the ILS for runway 28 at Dublin continued 800 feet below cleared altitude triggering an ATC safe altitude alert which then led to a go around from around 1000 feet when still over 5nm from the landing runway threshold. The Investigation attributed the event broadly to the Captain’s inadequate familiarity with this EFIS-equipped variant of the type after considerable experience on other older analogue-instrumented variants, noting that although the operator had provided simulator differences training, the -600 was not classified by the certification authority as a type variant.

On 13 September 2016, a Boeing 737-300 made an unstabilised approach to Wamena and shortly after an EGPWS ‘PULL UP’ warning due to the high rate of descent, a very hard landing resulted in collapse of the main landing gear, loss of directional control and a lateral runway excursion. The Investigation found that the approach had been carried out with both the cloudbase and visibility below the operator-specified minima and noted that the Captain had ignored a delayed go around suggestion from the First Officer because he was confident he could land safely as the two aircraft ahead had done.

On 29 January 2015, a Boeing 737-800 crew attempting to fly an NDB approach to Bergerac, with prior awareness that it would be necessary because of pre-notified ILS and DME unavailability, descended below 800 feet agl in IMC until an almost 1000 feet per minute descent when still over 8 nm from the runway threshold triggered an EGPWS ‘TERRAIN PULL UP’ warning and the simultaneous initiation of a go-around. The Investigation found that the PF First Officer was unfamiliar with NDB approaches but had not advised the Captain which resulted in confusion and loss of situational awareness by both pilots.

On 26 August 2019, an Airbus A320 attempted two autopilot-engaged non-precision approaches at Birmingham in good weather before a third one was successful. Both were commenced late and continued when unstable prior to eventual go-arounds, for one of which the aircraft was mis-configured causing an ‘Alpha Floor’ protection activation. A third non-precision approach was then completed without further event. The Investigation noted an almost identical event involving the same operator four months later, observing that all three discontinued approaches appeared to have originated in confusion arising from a slight difference between the procedures of the aircraft operator and AIP plates.

 

Stabilised Approach Awareness Toolkit for ATC

Further Reading

CANSO

Part of the Stabilised Approach Awareness Toolkit for ATC

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