26th September 2016
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Autopilot recommendations after lightning strike on Sumburgh-bound flight

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A Sumburgh-bound aircraft carrying 30 passengers nose-dived after being struck by lightning because efforts by the crew to lift the aeroplane’s nose and climb were overruled by the onboard autopilot system.

An air accident report into the December 2014 incident has found the Loganair Saab 2000 fell rapidly after being struck on its journey from Aberdeen.

Passengers spoke at the time of hearing a bang like a “gunshot” along with a big white flash.

The plane quickly lost altitude and reached a peak descent rate of 9,500 feet per minute. However, the aircraft started to climb after reaching a minimum height of 1,100 ft above sea level.

The new Saab 2000 aircraft operated by Loganair/Flybe made its first landing at Sumburgh on Wednesday. The aircraft is currently undergoing trials and training before being brought into service on the Sumburgh route later this year. Photo: Ronnie Robertson

A Saab 2000 aircraft operated by Loganair/Flybe like the one which was struck by lightning in December 2014. Photo: Ronnie Robertson

It flew back to Aberdeen where it made a safe landing.

The Air Accident Investigation Branch has made a series of safety recommendations concerning the autopilot system.

In a 74-page report released today, the AAIB says: “During the approach phase of a routine flight the aircraft was struck by triggered lightning. Procedures intended to prevent flight in areas where lightning may be encountered do not protect against triggered strikes.”

The report adds that the lightning caused only minor damage. Functional tests and inspections carried out after the aircraft had landed did not reveal any faults.

However, it states evidence from the manufacturer’s simulation work indicated the aircraft had responded “as expected” to the recorded control deflections.

“The commander’s actions following the lightning strike were to make manual inputs on the flying controls, which appear to have been instinctive and may have been based on his assumption that the autopilot would disconnect when
lightning struck.

“However, the autopilot did not disconnect and was attempting to maintain a target altitude of 2,000 feet amsl [above mean sea level] by trimming nose-down while the commander was making nose-up pitch inputs.

“The control forces felt by the commander were higher than normal because the autopilot was opposing his inputs and he may have attributed this to a flight control malfunction caused by the lightning strike.”

The report adds that the commander applied and maintained “full aft control column (nose-up elevator) input”. However, the autopilot’s “nose-down elevator trim authority exceeded the commander’s elevator nose-up authority and the aircraft pitched nose-down and descended, reaching a peak descent rate of 9,500 ft/min”.

“The autopilot then disengaged … and this allowed the commander’s nose-up pitch trim inputs to become effective. “The aircraft started to pitch up just before reaching a minimum height of 1,100 ft above sea level.

“If the autopilot system had been designed such that operating the pitch trim switches resulted in autopilot disengagement, the autopilot would also have disengaged early in the sequence of events.”

The main thrust of the five safety recommendations are that the design of the Saab 2000’s auto-pilot system be reviewed and modifications made to ensure the system “does not create a potential hazard when the flight crew applies an override force to the flight controls”.

 

The autopilot did not disconnect and was attempting to maintain a target altitude of 2,000 feet.

Loganair’s director of flight operations Andy Thornton said: “We welcome the findings of the report published by the AAIB and take on board its content.

“Immediately following this incident, Loganair issued enhanced guidance in consultation with the aircraft manufacturer to all company pilots flying the Saab 2000.

“We also amended our training syllabus and worked with our third-party provider to augment and refine training procedures to include a scenario similar to that experienced by our flight crew in December 2014.

“Our pilots regularly go through extensive training and Loganair prides itself on the excellent standards and quality of its pilot workforce.”

AboutRyan Taylor

Ryan Taylor has worked as a reporter since 1995, and has been at The Shetland Times since 2007, covering a wide variety of news topics. Before then he reported for other newspapers in the Highlands, where he was raised, and in Fife, where he began his career with DC Thomson. He also has experience in broadcast journalism with Grampian Television. He has lived in Shetland since 2002, where he harbours an unhealthy interest in old cars and motorbikes.

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