Date:	Friday 9 April 2021
Time:	05:19 UTC
Type:	British Aerospace ATP
Owner/operator:	West Air Sweden
Registration:	SE-LPS
MSN:	2043
Year of manufacture:	1991
Engine model:	Pratt and Whitney Canada PW126A
Fatalities:	Fatalities: 0 / Occupants: 3
Aircraft damage:	None
Category:	Serious incident
Location:	Isle Of Man-Ronaldsway Airport (IOM/EGNS) -   United Kingdom
Phase:	Approach
Nature:	Cargo
Departure airport:	East Midlands Airport (EMA/EGNX)
Destination airport:	Isle Of Man-Ronaldsway Airport (IOM/EGNS)
Investigating agency:	AAIB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
BAe ATP SE-LPS was on approach to the Isle of Man with the co-pilot as Pilot Flying. As the aircraft approached the minimum descent altitude, the co-pilot attempted to disconnect the autopilot. There was no audio tone to indicate the disconnection and the co-pilot felt there was resistance in the controls. Both pilots checked the cockpit indications which seemed to show that the autopilot had been successfully disconnected. The commander took control, and also felt resistance in the controls. He pressed and held the synchronisation (SYN) button on the control column which he felt released the controls and he was able to land normally.

AAIB Conclusion
The investigation concluded that the anomalies with the audio warnings were probably associated with corrosion and moisture caused by water ingress through the DV windows.

The AAIB was unable to replicate the reported anomalies in the autopilot system, but theoretical analysis by the autopilot manufacturer identified a scenario involving the autopilot disconnect button and the associated debounce circuit that could lead to a partial disengagement of the autopilot. This scenario could explain the previous occurrences on G-BUUR and SE-MHF but would only partially explain the occurrence to SE-LPS.

Although the aircraft abnormal and emergency checklist did contain a procedure for the failure of the autopilot to disengage, the commander reacted instinctively due to his awareness of a previous occurrence that he had read about in an AAIB report. While the slipping clutch is designed to allow the crew to overpower an autopilot that does not disengage, a substantial increase in the force required to operate the flying controls when late on the approach could present an increased safety risk to the aircraft. The commander used the syn button which allowed him to operate the controls without hindrance and land the aircraft without further incident

1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/62fe888d8fa8f504c2518280/BAe_ATP_SE-LPS_10-22.pdf
2. https://www.planespotters.net/airframe/british-aerospace-bae-atp-se-lps-west-air-sweden/rzw2xz
3. https://www.flightera.net/en/planes/SE-LPS
4. https://en.wikipedia.org/wiki/West_Air_Sweden
5. https://en.wikipedia.org/wiki/Isle_of_Man_Airport

During a flight descending to Ronaldsway Airport on the Isle of Man in April 2021, a BAe ATP (SE-LPS) had resistance in the flying controls after the autopilot failed to disengage.

Read the report: https://t.co/BiQjIMuAn9#AviationSafety pic.twitter.com/cGvl0hyyN0

— AAIB (@aaibgovuk) August 25, 2022

Anniversary statement on the AAIB investigation into a serious incident involving a BAe ATP, SE-LPS, at Isle of Man / Ronaldsway Airport on 9 April 2021.https://t.co/1yIAGNjual

Read more about how we investigate aircraft accidents:https://t.co/1ptiUNyF14 pic.twitter.com/QhSGSg1o1b

— AAIB (@aaibgovuk) April 8, 2022

British Aerospace ATP West Air Europe SE-LPS , landing at Runway 22 at Birmingham (BHX) on 15 May 2022: British Aerospace ATP-F of West Atlantic on approach to Runway 33 at Birmingham (BHX), 15/09/18. British Aerospace ATP-F of West Atlantic Sweden at East Midlands (EMA), 02/06/22.

#WestAir #Sweden, British Aerospace #BAe #ATP SE-LPS at East Midlands Airport 6th August. New to #BritishAirways in 1991 as G-BTPM. #BAeATP #BritishAerospace #Cargo #AvGeek #AvGeeks #PlaneSpotting #potn #Aviation pic.twitter.com/2HRfr6Znip

— aviationathan (@aviationathan) September 3, 2020

Date/time	Contributor	Updates
29-May-2022 18:06	Dr. John Smith	Added
25-Aug-2022 12:20	harro	Updated [Time, Departure airport, Source, Embed code, Damage, Narrative, Accident report]
25-Aug-2022 16:35	Dr. John Smith	Updated [Source, Embed code, Narrative]