Date:	Wednesday 2 January 2019
Time:	12:55 UTC
Type:	Bell 429 GlobalRanger
Owner/operator:	Wiltshire Air Ambulance
Registration:	G-WLTS
MSN:	57191
Year of manufacture:	2014
Engine model:	Pratt and Whitney Canada PW207D1
Fatalities:	Fatalities: 0 / Occupants: 2
Aircraft damage:	None
Category:	Serious incident
Location:	Melksham Airfield, Bowerhill, Melksham, Wiltshire -   United Kingdom
Phase:	Take off
Nature:	Test
Departure airport:	Melksham Airfield, Bowerhill, Melksham, Wiltshire
Destination airport:
Investigating agency:	AAIB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
AAIB investigation to Bell 429 GlobalRanger, G-WLTS: Un-commanded yaw during Power Assurance Check, Melksham, Wiltshire, 2 January 2019. The AAIB Final Report was published on 30 April 2020, and it should be noted, the report refers to two separate events with the same helicopter, one on 15 June 2018, and one on 2 January 2019. The following is the summary from that report:

"The report considers two events which occurred while the pilot was conducting a Power Assurance Check. In one, an un-commanded yaw pedal movement caused a rapid rotation of the helicopter through two and a half complete rotations; in the other, a trim runaway was contained by the pilot. The trim runaway was found to be an unknown feature of the Automatic Flight Control System logic.

Following these events, safety action was taken by the helicopter manufacturer and Transport Canada to help crews respond to a yaw trim runaway and to address the underlying causal factor. Also, the flight recorder manufacturer improved the way it reported the results of CVR recording inspections.

Two Safety Recommendations are made: one to Transport Canada in relation to conduct of the Power Assurance Check; and one to the European Union Aviation Safety Agency to ensure that the installation of new equipment on aircraft does not have a detrimental effect on existing equipment".

There is also an entry on Wikipedia which refers to these incidents (see link #3):

"2018 service interruptions
The helicopter was out of service for over a month in June and July 2018, while a technical failure was investigated. Flight operations were also suspended for two weeks in August 2018 as the aircraft, vehicles and airbase buildings were examined to ensure no contamination resulting from the 2018 Amesbury poisonings was present. The aircraft did not respond to the poisonings as it was again grounded due to a technical failure, but there was concern that traces of Novichok agent may have been transferred onto equipment used by critical care paramedics who responded in rapid response vehicles (RRV). The charity later said the interruption had resulted in additional costs of £100,000.

2019 grounding
In early January 2019, the helicopter was grounded after an incident during pre-flight checks, which was similar to the June 2018 incident. The situation was complicated by the entry into voluntary liquidation of Heli Charter, who supplied the aircraft and were the holder of the air operator certificate (AOC). Medical provision continued by way of RRV, before the service returned to flying on 11 January 2019 with the delivery of a temporary MD 902 supplied by Specialist Aviation Services, the company that supplied the aircraft shared with Wiltshire Police until 2014.

The charity declared its intention to apply for its own AOC to allow it to operate the Bell 429 directly, but cautioned that this could not occur until the cause of the January incident had been established.[19] In response to this incident and two more elsewhere, the helicopter's manufacturer issued changes to the Flight Manual in April. The Civil Aviation Authority (CAA) completed inspections in August and issued the AOC in November, enabling the Bell 429 to re-enter service. The CAA's delay had been criticised by local MP Michelle Donelan in October, and in December Private Eye magazine claimed that the CAA had "dragged its feet" and stated that the charity had made a formal complaint to the CAA.

In April 2020, the Air Accidents Investigation Branch (AAIB) published their report into the 2018 and 2019 incidents, which were together classed as a "serious incident". The report called for Bell Textron, the helicopter manufacturer, to improve the procedure for conduct of the Power Assurance Check; Bell also undertook to make future improvements to the flight control system software. The AAIB also found that the cockpit voice recorder had been affected by the fitting of TETRA communications equipment in 2015, and the defect had not been found during annual checks by the recorder's manufacturer, leading to a recommendation to the European Aviation Safety Agency regarding checks to be made after adding equipment".

1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/5f45120dd3bf7f69a9d62652/Bell_429_G-WLTS_05-20.pdf
2. AIB Annual Safety Review 2020 (pp.87-88): https://assets.publishing.service.gov.uk/media/60d2e72ed3bf7f4bd4662d67/Annual_Safety_Review_2020.pdf
3. https://en.wikipedia.org/wiki/Wiltshire_Air_Ambulance#2019_grounding
4. https://en.wikipedia.org/wiki/Bowerhill
5. https://www.wiltshireairambulance.co.uk/wiltshire-air-ambulance-resumes-flying-operations
6. https://www.wiltshiretimes.co.uk/news/18294498.mps-battle-get-air-ambulance-100-000-compensation-novichok-attacks/
7. https://helihub.com/2019/01/04/wiltshire-air-ambulance-grounded-by-heli-charter-liquidation/
8. https://www.wiltshireairambulance.co.uk/wiltshire-air-ambulance-to-resume-flying-this-week
9. https://www.airport-data.com/aircraft/G-WPAS.html
10. https://www.wiltshireairambulance.co.uk/keeping-you-updated
11. https://ad.easa.europa.eu/ad/CF-2019-16
12. https://www.swindonadvertiser.co.uk/news/18028122.wiltshire-air-ambulance-back-air/
13. https://michelledonelan.co.uk/wiltshire-air-ambulance/
14. https://www.gazetteandherald.co.uk/news/18418583.report-investigates-out-of-control-wiltshire-air-ambulance-helicopter/

G-WLTS Bell 429 Helicopter Wiltshire Air Ambulance on 18 April 2018

Date/time	Contributor	Updates
26-Jun-2021 21:34	Dr. John Smith	Added
26-Jun-2021 21:35	Dr. John Smith	Updated [Embed code, Narrative]
26-Jun-2021 21:35	Dr. John Smith	Updated [Nature]
26-Jun-2021 21:37	Dr. John Smith	Updated [Source, Narrative]
29-Apr-2022 19:02	harro	Updated [Accident report]