This serious incident was notified to the Air Accidents Investigation Branch (AAIB) by ATC at the Isle of Man (Ronaldsway) Airport, at 1855 hrs on 23 May 2005. The following Inspectors participated in the investigation:
Mr P T Claiden Investigator in Charge
Mr T Atkinson Operations
Mr A H Robinson Engineering
Mr P Wivell Flight Recorders
Under the Isle of Man Civil Aviation (Subordinate Legislation) (Application) Order 1992, the United Kingdom Civil Aviation (Investigation of Air Accidents) Regulations 1989 are applicable in the Isle of Man. Accordingly, Inspectors of Air Accidents from the AAIB carried out an investigation into this occurrence.
The aircraft was configured with 64 seats; 33 passengers were on board. Shortly after takeoff, a seal associated with the retraction line for the hydraulically operated integral airstairs at the front left cabin door, failed. This allowed hydraulic fluid to escape in the form of a fine mist, depleting the contents of the main hydraulic system. This misting was perceived by the cabin crew as smoke, and they informed the flight crew accordingly. In flight, this line is normally de-pressurised but, owing to a jammed airstairs UP selection switch and a stuck door safety microswitch, it had remained pressurised.
The intensity of the misting in the forward section of the cabin led the cabin crew to reposition the passengers towards the rear of the cabin. As a result, the aircraft’s centre of gravity (CG) position moved beyond the operator’s specified aft limit.
An emergency was declared to ATC and the aircraft returned to Ronaldsway. During the approach, the EGPWS system alerted the crew to an incorrect flap setting for landing.
After landing, the aircraft was taxied clear of the runway but difficulties encountered with the nosewheel steering system forced the commander to stop the aircraft short of the terminal buildings. One passenger, who was asthmatic, was taken to a local hospital but later discharged as medical treatment was not considered necessary.
The investigation identified the following causal factors:
A combination of a stuck door safety microswitch plunger and a jammed-on airstairs UP switch caused hydraulic pressure to remain applied to the airstairs retraction actuators in-flight.
The failure of the hydraulic seal associated with the airstairs operating mechanism occurred in-flight; this resulted in the fluid contents of the main hydraulic system being discharged as a fine mist into the passenger cabin.
At the time of the incident, there were no periodic inspection or maintenance checks required on the airstairs operating system.
The rearward movement of the aircraft’s CG position beyond the aft limit as specified by the operator, was caused by the cabin crew moving passengers towards the rear of the cabin in an attempt to minimise their exposure to the ‘smoke’.
There was no requirement for cabin crews to obtain agreement from the commander prior to moving passengers towards the rear of the cabin although, on this occasion, the commander was informed of their actions.
The flight crew’s non-adherence to SOPs (Standard Operating Procedures) and associated checklists put the aircraft and its occupants at unnecessary increased risk from potential handling problems as well as risk of fire and prolonged exposure to hydraulic fluid mist.
One safety recommendation is made.
Download full report:
AAR 1/2007 - G-JEMC.pdf (1,444.41 kb)