Date:	Tuesday 22 March 2022
Time:	14:10 UTC
Type:	de Havilland Canada DHC-1 Chipmunk 22
Owner/operator:	Shipping And Airlines Ltd
Registration:	G-BXHA
MSN:	C1/0801
Fatalities:	Fatalities: 0 / Occupants: 2
Aircraft damage:	Minor
Category:	Serious incident
Location:	Sevenoaks, Kent -   United Kingdom
Phase:	Initial climb
Nature:	Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:	London-Biggin Hill Airport (BQH/EGKB)
Destination airport:	London-Biggin Hill Airport (BQH/EGKB)
Investigating agency:	AAIB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
DHC-1 Chipmunk G-BXHA sustained severe vibration due to cracked propeller assembly, over Sevenoaks, Kent.

During the initial climb after takeoff, the pilot noticed some subtle airframe vibration. However, due to a lack of recency on type, he could not recollect if the level of vibration was normal for the aircraft and elected to continue the flight.

During the flight the aircraft developed severe vibration requiring the pilot to return to the airfield where fatigue cracks were found in the propeller and its two mounting blocks. The cracks originated from fretting between the propeller assembly and splines on the engine hub.

While manoeuvring, the airframe vibrations increased abruptly and to a level that the pilot had difficulty reading the instruments. The pilot returned to the airfield where, during the taxi, the vibration caused the low voltage warning light to fall out of the instrument panel.

At the time of this event, the propeller had flown 97 hours since the Servicing Bulletin was last carried out in April 2017.

=AAIB Conclusion=
The initiating failure of the propeller assembly was caused by fatigue cracking of the forward boss block and propeller, resulting from fretting and corrosion. The existing Servicing Bulletin to inspect the propeller assembly does not specify inspection of the inner diameter of the boss blocks for wear or corrosion.

As a result of this investigation, the aircraft Type Responsibility Agreement holder, the CAA and LAA are taking the following Safety Action:

=Aircraft Type Responsibility Agreement holder=
Will promulgate a Technical News Sheet to its subscribers which will include enhanced guidance for continued airworthiness of Fairey Reed propellers. This will include the use of Non-Destructive Testing, and inspections for corrosion, fretting and correct surface finish.

NOTE: Although the AAIB report refers to "Sevenoaks, Kent", G-BXHA operates out of London Biggin Hill Airport (BOH/EGKB). Sevenoaks, Kent is where the incident took place, as the aircraft flew south east from Biggin Hill, which is approx. 12 miles away.

1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/63c807c6e90e07684cde3e56/DHC-1_Chipmunk_22_G-BXHA_02-23.pdf
2. AAIB Annual Safety Review 2023 p.101: https://assets.publishing.service.gov.uk/media/6604534991a320001182b13d/AAIB_Annual_Safety_Review_2023.pdf
3. https://www.ukserials.com/results.php?serial=WP
4. Owners Website: https://shippingandairlines.co.uk/historic-aircraft/chipmunk/
5. https://en.wikipedia.org/wiki/London_Biggin_Hill_Airport

WP925 was manufactured at de Havilland\\\'s Broughton (Hawarden) factory in late 1952 and then was delivered into service with the Royal Air Force on the 6th January 1953. She was then stored until 27th May 1953 when she was issued to the Light Aircraft School at Middle Wallop. She served here until the end of the AAC use of the Chipmunk for training on 27th March 1997. Struck off charge and civil registered as G-BXHA 20th May 1997. The aircraft has had seven UK-registered civilian owners since then, including a spell as G-HVII between 14 May 2019 and 30 March 2020, after which date it reverted to G-BXHA

DHC-1 Chipmunk G-BXHA (still in original military markings as "WP925") at Turweston Aerodrome (EGBT) - VAC Spring Fly In 15 April 2023

Date/time	Contributor	Updates
30-Mar-2024 07:01	Dr. John Smith	Added
30-Mar-2024 07:01	ASN	Updated [Narrative, Accident report]