A Flybe de Havilland Dash 8-400, registration G-FLBB performing flight Be-664 from Knock (Ireland) to Manchester,EN (UK) with 74 people on board, was climbing through FL180 out of Knock when the crew reported smoke in the cockpit and decided to divert to Dublin. Dublin tower advised other aircraft on frequency about the ongoing emergency stating there was smoke on board of the aircraft, they subsequently lost communication with the aircraft, the aircraft was just squawking emergency. The crew subsequently later reported on frequency, stated they had mist and a burning odour rather than smoke, the aircraft landed safely on Dublin’s runway 28 about 18 minutes after stopping the climb.
The airline reported a toilet smoke detector triggered.
On Jun 20th 2016 the AAIU released their final factual report without formal conclusion, however stating the engine manufacturer’s conclusions:
high unbalance of the HP rotor resulted in distress of the carbon seals resulting in oil leak into the gas path
The AAIU stated that the aircraft was climbing through FL170, first officer was pilot flying, when the flight crew detected an unusual odour on the flight deck, checked the engine instruments and found the left hand engine’s InterTurbine Temperature (ITT) was higher than the right hand engine’s, however, was still within acceptable operational limits. Shortly after cabin crew informed the flight deck that a lavatory smoke detector had activated and there was visible smoke near the ceiling of the cabin. The flight crew levelled the aircraft at FL190, donned their oxygen masks, observed smoke on the flight deck apparently emanating from the panels to the left of the captain’s (63, ATPL, 7,264 hours total, 2,354 hours on type) seat. The crew declared PAN, descended the aircraft to FL100 and explored nearest suitable airfields with ATC where to divert to, then decided to divert to Dublin. After landing the captain assessed, that an immediate evacuation was not necessary, emergency services did not detect any source of fire or heat, and the aircraft taxied to the apron, where passengers disembarked normally.
The source of the smoke could not be immediately identified.
Two days later, an operator’s engineer intended troubleshooting and started the #1 engine for a low power engine run and was immediately alerted to a lot of smoke coming from an engine vent and the drain mast and shut the engine down. A large amount of engine oil was found in the engine’s ducting, the oil quantity appeared low. A borescopic inspection identified an oil leak at the Handling Bleed-Off Valve (HBOV). The engine was removed and sent for overhaul.
The maintenance facility identified the #4 bearing key washer showed distress and concluded: “high unbalance of the HP rotor resulted in distress of the carbon seals resulting in oil leak into the gas path”.
The AAIB reported the engine manufacturer took following actions:
On 26 January 2016, the Engine Manufacturer issued a Service Information Letter (SIL No. PW150-058) to all operators highlighting the root cause and preventative action to be taken.
The Engine Manufacturer identified that:
‘The distress condition of some washers, had resulted in metal chips being released into the oil system with possible symptoms being reported as loss of oil sealing, loss of oil pressure, cabin air contamination and in some cases In Flight Shut Down (IFSD) of the affected engine’
The cause of the washer wear (distress) was identified as stress in the filet radius of the key washer which may initiate cracks that could propagate until there is material release.
An improved key washer with an ‘infinite life’ was designed by the Engine Manufacturer and was made available from 29 February 2016. In the interim period until such replacements were made, the Engine Manufacturer developed and implemented several actions aimed to reduce the incidence of events related to the distress of the Key washer component.
The AAIU commented that the crew actions were appropriate, the necessary actions were taken.
The AAIU further commented: “The Engine Manufacturer has identified the cause of the No. 4 Bearing Key washer distress and issued guidance for inspection and replacement of the part. In addition, the part has been redesigned for an ‘infinite life’ on replacement and accordingly this Investigation does not sustain any Safety Recommendations.”
The #4 bearing key washer showing distress (Photo: AAIU):
To read the Av Herald report click here