The aircraft had departed Ireland West Airport (EIKN) and was climbing through 17,000 ft when the Flight Crew were alerted by a strange odour/fumes on the flight deck followed by activation of the forward toilet smoke alarm. With smoke becoming visible in both the cabin and flight deck, the Flight Crew donned their oxygen masks. The flight diverted to Dublin Airport (EIDW) where it landed at 17.41 hrs, without further incident. There were no injuries.
Subsequent trouble-shooting by maintenance personnel revealed the presence of oil in the Handling Bleed-Off Valve (HBOV) caused by failure of carbon seals due to distress and rupture of the No. 4 Bearing Key washer in the No. 1 engine. Contamination of the secondary oil system due to the damaged seals caused fumes to enter the cabin and flight deck.
The AAIU was notified by the Air Traffic Control (ATC) Station Manager at Dublin Airport at 16.34 hrs while the aircraft was still airborne. One Inspector of Air Accidents travelled to Dublin Airport and spoke with the aircraft crew.