A plane asked to perform a go-around at Aberdeen Airport descended for 57 seconds without air crew noticing, according to a report.
The Tui operated Boeing 737 was flying from Majorca to Aberdeen on September 11 last year when the incident occurred.
Air traffic controllers asked the crew onboard the flight to delay their approach due to a search and rescue helicopter waiting to take off.
The aircraft initially climbed but before it reached the required cleared altitude of 3,000ft, it began to descend.
A ‘serious incident’
It descended around 1,200ft for 57 seconds before action was taken.
The Air Accidents Investigation Branch (AAIB) said it was likely unnoticed by crew due to being overloaded by the “high workload” onboard during the go-around.
After seeing the “unexpected” descent, the radar controller contacted crew to instruct them to pitch back into a climb just as onboard crew had taken action.
The Tui aircraft, holding 67 passengers and six crew, climbed again before it landed safely with no further problems.
The report said it was a “serious incident” that showed a “significant deviation” from the expected flight path.
Acknowledging that crew might have been distracted by the high workload at the time, the report also noted the air crew’s lack of flying hours due to Covid could also have contributed to the incident.
More training and changes to procedures put in place
Following the unnoticed descent, the report said safety actions have been implemented.
It said: “Aberdeen ATC changed its procedures for aircraft being broken off from the approach, and the aircraft manufacturer issued guidance to pilots about the behaviour of the Autopilot and Flight Director System (AFDS) and autothrottle during go-arounds.
“The aircraft operator informed all its pilots about the event; included extensive go-around training in its training cycle; and completed a full review on pilot recency, which introduced additional restrictions to manage pilots through periods of reduced flying.”
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