DH8D, en route, west-northwest of Dublin Ireland, 2015

DH8D, en route, west-northwest of Dublin Ireland, 2015


On 31 July 2015 a Bombardier DHC8-400 crew detected the presence of abnormal fumes on the flight deck and were then advised by the cabin crew that the forward toilet smoke alarm had been activated and that smoke was visible in the cabin. Smoke then appeared in the flight deck and a PAN was declared. A diversion to Dublin was subsequently made. The Investigation found that debris from a fractured bearing washer had compromised engine oil seals leading to fumes/smoke entering the aircraft through the air conditioning system. The manufacturer has since introduced a new infinite life bearing washer.

Event Details
Event Type
Flight Conditions
Flight Details
Type of Flight
Public Transport (Passenger)
Intended Destination
Actual Destination
Take-off Commenced
Flight Airborne
Flight Completed
Phase of Flight
En-route Diversion
Non-Fire Fumes
PAN declaration
Engine - General
Component Fault in service
Damage or injury
Aircraft damage
Non-aircraft damage
Non-occupant Casualties
Number of Non-occupant Fatalities
Number of Occupant Fatalities
Off Airport Landing
Causal Factor Group(s)
Aircraft Technical
Safety Recommendation(s)
None Made
Investigation Type


On 31 July 2015 a Bombardier DHC8-400 (G-FLBB) on a scheduled international passenger flight from Ireland West/Knock to Manchester, UK and climbing through FL170 in day VMC experienced smoke and fumes in both the passenger cabin and the flight deck. A 'PAN' was declared to ATC, a descent to FL100 accomplished and oxygen masks were donned by both pilots. The smoke and fumes situation persisted but stabilised and a diversion to Dublin was made. After engine shutdown, the smoke/fumes began to clear and it was not possible to identify the source of the fumes/smoke. No ill effects were reported to have been suffered by any of the 78 occupants.


The event was investigated by the Irish Air Accident Investigation Unit (AAIU). The 63 year-old Aircraft Commander was recorded as having 7,264 hours total flying experience which included 2,354 hours on type.

It was established that with the First Officer acting as PF and the aircraft climbing through FL170, the pilots had both detected the presence of “a strange odour/ fumes” on the flight deck. The No. 1 engine ITT indication was noted to be “significantly higher” than that for the No. 2 engine, although it was within allowable limits. Soon after this, the senior member of the Cabin Crew advised that the forward toilet smoke alarm had activated and that there was smoke visible near the passenger cabin ceiling. The aircraft was levelled at FL 190 and both pilots donned their oxygen masks. By this time, smoke was also evident on the flight deck and “observed to be emanating from panels to the left of the Commander’s seat”. A ‘PAN’ was declared to ATC and an immediate descent made to FL 100. After considering the situation and diversion options, the Commander informed ATC that it was their intention to divert to Dublin.

The situation stabilised and the diversion was completed without any further complications with the First Officer continuing as PF. After landing, the Commander decided that an immediate evacuation was not necessary and after a visual external check of the aircraft by the AFS, the aircraft taxied to its parking stand and the passengers disembarked normally. An AAIU Inspector then spoke with the flight crew.

When a Company engineer tasked with investigating the problem subsequently started the No. 1 engine with the intention of carrying out a low power engine run, “he was alerted to a large amount of smoke coming from an engine vent and the drain mast” on that engine and shut it down immediately. Inspection disclosed a large quantity of oil in the engine ducting and a very low oil quantity indication. Borescope inspection was used to trace the fault to oil leaking from a Handling Bleed-Off Valve (HBOV) on the No. 1 engine and it was removed and sent for overhaul. It was noted that the removed Pratt & Whitney Canada P&W PW150A engine had been installed in the No. 1 position on G-FLBB in March 2011 having previously accumulated 820 hours and 5233 cycles since new. At the time of removal, the engine had reached 13,001 hours and 14,583 cycles.

Inspection of the engine at the overhaul facility to which it was sent found that the No. 4 Bearing Key washer had fractured and that as a direct consequence, the “high unbalance of the HP rotor resulted in distress of the carbon seals resulting in oil leak into the gas path”.

The fractured No 4 bearing key washer [Reproduced from the Official Report]

The Operator advised that including this event, there had been four unscheduled engine removals on its DH8-400 fleet in 2015 attributed to “oil smell/fumes” and a further six attributed fractures of the No. 4 Bearing Key washer, of which two had been associated with smoke and fumes.

Pratt & Whitney Canada advised that since December 2014, they were aware of 19 events in which the No. 4 Bearing Key washer on PW150A engines had failed and “in most cases the engine was subject to an unscheduled removal”. Four of the 19 events were stated to have involved an in-flight shutdown (IFSD) of the affected engine and in one case, the shutdown had been uncommanded.

Safety Action taken by Pratt & Whitney Canada in response to these events included the following:

  • In December 2015 it was decided to routinely replace the No. 4 bearing washer at each shop visit.
  • On 26 January 2016, a SIL had been issued to affected Operators /MROs explaining the root cause of the problem and preventative action to be taken. This advised 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” and that “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”.
  • On 29 February 2016, an improved key washer with an ‘infinite life’ was made available and until such replacements were made, interim actions to reduce the incidence of washer distress events were taken.

The Conclusions of the Investigation were that:

  • The Aircraft Commander had made appropriate decisions and took necessary actions during the event.
  • The cause of the No. 4 Bearing Key washer distress has been identified and the part has been redesigned so that an ‘infinite life’ will now apply on replacement with interim guidance for inspection and replacement of the pre-modification parts provided.

It was decided that “accordingly this Investigation does not sustain any Safety Recommendations”.

A Factual Report of the Investigation was published on 20 June 2016.

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