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Serious incident: Irish ATR-72 descends below glideslope in instrument conditions.
13 June 2014
Altitude versus Distance to threshold of RWY 26 (AAIU)

Altitude versus Distance to threshold of RWY 26 (AAIU)

The Irish AAIU concluded their investigation into a serious incident in which an ATR-72 descended below the glide path in IMC while on approach to Kerry Airport, Ireland.

On 19 December 2011, an ATR-72 of Aer Arann was being operated on a domestic passenger flight from Dublin to Kerry in Ireland. There were 13 passengers and four crew members on board.
The flight crew comprised a training captain (commander) and a captain, who was being line checked by the commander.

While the aircraft was conducting an ILS approach to runway 26 at EIKY with the autopilot engaged, difficulty was experienced in following the glideslope and the aircraft descended below the glide path.
As the aircraft passed over a ridge on the approach the Enhanced Ground Proximity Warning System (EGPWS) activated. At that time the aircraft was descending through an altitude of 2,246 ft, at a Radio Altimeter height of 959 ft above the ground and at a distance of 10.02 NM from the threshold of runway 26. At that time the rate of descent was 2,400 ft/min. The Terrain Warning occurred at an altitude of 2,100 ft when the Glideslope Deviation was showing a valid signal but which incorrectly showed that the aircraft was between 1 and 1.25 dots high.
A go-around was then initiated. Following this, a non-precision approach was flown which resulted in a successful landing. During that approach similar problems with the glideslope were experienced.

Probable Cause:
The absence of a Glideslope Antenna Deflector resulted in unstable glideslope signal reception which led to the autopilot descending the aircraft below the glide path in IMC.

Contributory Cause(s):

  1. Ineffective monitoring and lack of situational awareness by the Flight Crew.
  2. Inability of the EIKY ATC to monitor the aircraft due to lack of a radar display.

More information: