Date:	Wednesday 10 August 2022
Time:	16:40 LT
Type:	Bombardier CL-600-2B16 Challenger 604
Owner/operator:	Air Independence GmbH
Registration:	D-AAAY
MSN:	5602
Year of manufacture:	2004
Engine model:	General Electric CF34-3B
Fatalities:	Fatalities: 0 / Occupants: 10
Aircraft damage:	Minor
Category:	Serious incident
Location:	Farnborough Airport (FAB/EGLF), Farnborough, Hampshire -   United Kingdom
Phase:	Initial climb
Nature:	Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:	Farnborough Airport (FAB/EGLF)
Destination airport:	Málaga-Costa del Sol Airport (AGP/LEMG)
Investigating agency:	AAIB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
A Bombardier Challenger 604, D-AAAY, had an un-commanded flap extension, above the maximum flaps-extended speed in the climb after departing Farnborough Airport.

On the day of the occurrence, the crew arrived at Farnborough Airport at 13:00 hours to operate a private charter flight to Málaga – Costa Del Sol Airport, Spain. There were three crew and seven passengers on board.

The aircraft took off at 16:18 UTC on a private charter flight to Málaga–Costa Del Sol Airport, Spain. with three crew and seven passengers on board. Takeoff was performed from runway 06 using flap 20, after which the crew selected flap 0 to fully retract the flaps. Following a standard instrument departure to the south-west, the flight was cleared to climb to FL350. As the aircraft passed through FL190 at approximately 300 KIAS, with the autopilot engaged, the crew saw a FLAPS FAIL caution message on the EICAS display primary page. The co-pilot, who was the PF, reported that the aircraft pitched nose-up slightly and started to decelerate. The EICAS primary page also displays flap position information which indicated to the crew that the flaps were extending. The crew reported that the flap overspeed audio warning did not operate as they expected. The flap control lever was still in the flap 0 position selected by the crew after take-off.

The commander switched on the seatbelt sign and took control of the aircraft. He disengaged the autopilot, reduced thrust to slow down, and initiated a descent. The crew informed ATC of the situation, requesting a descent to FL100 and radar vectors to Gatwick Airport. Subsequently, they decided to divert to Farnborough as it was closer than Gatwick and avoided extending the flight longer than necessary.

The crew established that the aircraft was responding normally to control inputs and decided to maintain FL150 at approximately 180 KIAS, which was below the VFE of 189 KIAS for flap 45. They reported that it required nearly full power to maintain this condition. The autopilot was re-engaged. The cabin crewmember made a visual inspection of the flaps from the cabin and reported that they appeared to be fully extended and symmetrical. The crew consulted the ‘FLAPS FAIL’ procedure in the ‘Non-normal Procedures’ section of the Quick Reference Handbook and found that no further actions were required. They established that they would land approximately 1,000 lb over the maximum landing weight of 38,000 lb and planned to increase the landing reference speed (V REF) accordingly.

The aircraft was positioned for an ILS approach to runway 06 at Farnborough and the crew configured the aircraft for landing, selecting the flap control lever to the flap 45 position to match the observed flap position. The aircraft landed without further incident at 16:51 hours, at an airspeed of 135 Knots IAS.


Conclusion
This serious incident occurred because there was an uncommanded flap movement, which the flap protection system did not stop.
The reason for the uncommanded flap extension could not be identified.
The failure to arrest the uncommanded flap movement was caused by the welding of the D contacts in the No 1 flap retract relay which prevented it from operating. This welding probably occurred because of an unsuppressed back-EMF when the BDU brake solenoid was de-energised.

1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/65a7dcedb2f3c6000de5d42c/Bombardier_CL-600-2B16__604__D-AAAY_02-24.pdf
2. AAIB Special Bulletin #2, 2nd March 2023: https://www.gov.uk/government/news/aaib-special-bulletin-bombardier-cl-600-2b16-604-d-aaay
3. AAIB Special Bulletin S2/2022: https://assets.publishing.service.gov.uk/media/6329b74bd3bf7f75c989d8e4/S2-2022_Bombardier_CL-600-2B16__604__D-AAAY.pdf
4. https://www.gov.uk/government/publications/aaib-current-field-investigations/air-accidents-investigation-branch-current-field-investigations
5. https://forums.x-pilot.com/forums/topic/25721-cl60-d-aaay-uncommanded-flap-extension-aaib-initial-report/
6. https://www.radarbox.com/data/registration/D-AAAY
7. https://en.wikipedia.org/wiki/Farnborough_Airport

D-AAAY Bombardier 604 on approach to Runway 25L at Frankfurt (FRA) Germany, 16.8.2017.

A report into a serious incident involving a Bombardier CL-600 2B16 (604 variant), D-AAAY, in the climb from Farnborough Airport, Hampshire, 10 August 2022 has been published https://t.co/3DjCBcBnum#Aviation #AviationSafety pic.twitter.com/bAn28wwvBk

— AAIB (@aaibgovuk) January 18, 2024

Date/time	Contributor	Updates
24-Sep-2022 18:58	Dr. John Smith	Added
24-Sep-2022 19:00	Dr. John Smith	Updated [Time, Embed code, Narrative]
24-Sep-2022 19:01	Dr. John Smith	Updated [Operator]
26-Sep-2022 07:23	harro	Updated [Aircraft type, Location]
26-Sep-2022 07:34	harro	Updated [Operator, Source, Narrative]
02-Oct-2022 19:36	Dr. John Smith	Updated [Source, Narrative]
17-Oct-2022 21:24	Dr. John Smith	Updated [Destination airport, Narrative]
17-Oct-2022 21:24	Dr. John Smith	Updated [Narrative]
18-Jan-2024 20:29	Dr. John Smith	Updated [Location, Source, Embed code, Narrative, Category]
18-Jan-2024 20:32	harro	Updated [Other fatalities, Embed code, Damage, Narrative, Accident report]