'Ice build-up behind air emergency'

The flight was bound for Belfast City airport

A build-up of ice or of de-icing fluid may have caused an air emergency on a Belfast-bound flight in which four people were injured.

A report by the Air Accident Investigation Branch said further investigations would be carried out after it failed to find conclusive reasons for the incident.

Four people sustained injuries during an emergency on a flight from Birmingham in December last year.

The crew of the Flybe aircraft, formerly British European, reported an emergency situation after the plane underwent a "severe and unexpected movement" during the flight to Belfast City Airport.

A male flight attendant suffered a broken leg when he was knocked to the ground while a female crew member sprained her ankle.

Airline passenger Alan Lowry

Another crew member suffered head injuries and all three were taken to hospital.

A passenger also suffered minor head injuries but did not need hospital treatment.

One passenger on the plane said the aircraft shuddered violently before going into a brief nose dive.

Alan Lowry said the pilot quickly brought it under control and circled a few times before landing at Belfast.

The BAe 146-200 aircraft was carrying 36 passengers and five crew.

'Contained grease'

The branch, part of the Department of Transport, said the UK Low Level Forecast for the route had warned of severe icing in freezing rain and moderate icing in cloud on the day of the incident.

It said initial analysis of data showed symptoms of increased stiffness in the elevator servo tabs in the control system, possibly due to freezing.

The report said further investigations would examine the possibility of natural airframe icing, the effects of de-icing fluid residues and the implications of component failures within the pitch control system.

The branch revealed that when the aircraft elevators were disassembled, bearings which should have contained grease were found to contain "a dried, almost powdery residue which provided no lubrication properties".

"This raises concerns that moisture ingress into the bearing cage void could cause the bearings to seize as the moisture freezes in flight," it said.