Description

On 1 August 2008, an Embraer 195 being operated by Flybe on a scheduled passenger service from Manchester to Belfast City with the No 2 air conditioning pack inoperative in accordance with the Minimum Equipment List (MEL) was passing FL 156 in the climb in day Instrument Meteorological Conditions (IMC) approximately 40 nm northwest of Liverpool when the No 1 Air Cycle Machine (ACM) failed, releasing smoke and fumes into the aircraft. A MAYDAY was declared to ATC and a diversion to the Isle of Man was carried out. After donning oxygen masks the pilots had great difficulty communicating with each other, ATC and cabin crew, because of technical problems with the masks. During the subsequent emergency evacuation ordered by the aircraft commander, the right over-wing emergency exit door became jammed and unusable and five of the 94 occupants sustained minor injuries when using the main exit slides.

Investigation

An Investigation was carried out by the UK AAIB. The aircraft was fitted with two DVDRs from relevant data were downloaded. It was noted that the Captain, who had been PF for the flight, had a total 6500 flying hours which included 410 hours on type. In addition to the failure of the only serviceable ACM, this examined crew and RTF communications difficulties whilst the pilots wore oxygen masks and difficulties which became apparent during the emergency evacuation.

Examination of the failed No 1 pack ACM showed that its rotor had seized, the same component fault which had led to the failure of the No 2 air conditioning system on the same aircraft four days earlier. It was found that both ACMs had suffered Stage 2 turbine blade failures with the resultant imbalance resulting in contact between the turbine blade tips and the ACM casings which produced hot, finely divided, metallic particles that were released into the cabin air system, creating the reported symptoms of haze, ‘smoke’ and fumes inside the aircraft. The blade fatigue failures were both close to the blade root and were attributed to fatigue cracking originating in a location of high stresses associated with a known blade resonance condition. The Investigation was told that a new Stage 2 turbine housing was under development to address the problem.

In respect of crew communications, it was found that intercom and radio use whilst the flight crew had been wearing their oxygen masks had proved very difficult due to technical problems with the masks. Because of this, the cabin crew had to implement emergency procedures to gain access through the locked flight deck door to receive their instructions. The First Officer also had to repeat calls to ATC to make himself understood and communications between the two pilots were rendered so poor that they had to resort to shouting. In the light of findings by the Investigation on the reasons for these problems, the mask manufacturer reported having undertaken a detailed review of its design and manufacturing processes which resulted in design modifications and the addition of manufacturing quality checks.

Difficulties with the emergency evacuation included use of the over-wing exits. The right over-wing exit became jammed and unusable because of an inappropriate trim design at the exit and passengers who evacuated via the left over-wing exit reported than having been unsure of the right way to get from the wing down to the ground. It was also found that none of the passengers had evacuated the aircraft via D1R which was attributed to the staggered layout of the front two emergency exits with D1L being the main access door and the first to be encountered and D1R being further forward, behind a galley bulkhead and not a door normally used by passengers. Many passengers commented that they had found the main exit slides very steep and were surprised by the speed at which they slid down them and that the slides ended without any round-out at the bottom causing them to slide straight onto the ground at speed. This, and attempts by people to slow themselves on the slides, were the main causes of minor injury to five occupants of out the 95 persons on board during the evacuation. It was noted that the issue of ambiguous over-wing exit escape route markings had been the subject of an AAIB Safety Recommendation in 2002 in respect of certification of such exits on all types, but that this had been ignored by the JAA.

Two Safety Recommendations , the first of which was a re-issue of a 2002 one to the former JAA which had been ignored, were made as follows:

• that the European Aviation Safety Agency review the design, contrast and conspicuity of wing surface markings associated with emergency exits on Public Transport aircraft, with the aim of ensuring that the route to be taken from wing to ground is marked unambiguously.

[2010-007]

• that Embraer modify the over-wing emergency exits on Embraer 195 aircraft, to eliminate the possibility of the exit door jamming due to interference between the door trim panel and the ceiling edge panel.

[2010-008]

The Final Report of the Investigation was published on 10 June 2010.

Further Reading

• Airworthiness - The System
• Defect Assessment
• Unidentified Fire On Board (OGHFA SE)
• Decision-Making (OGHFA BN)