The day before the incident, during a cross-bleed engine start, the co-pilot noticed a brief acidic smell that returned just before takeoff and twice during the climb. The commander was unable to detect anything unusual until they were in the cruise, when the smell returned with increasing intensity. The smell was strongest in the area of the co-pilot’s rudder pedals and side-stick controller but there were no symptoms in the passenger cabin. The crew initiated the Smoke/Fire/Fumes emergency checklist and with the smell becoming stronger, they diverted to Bordeaux, where the landing was uneventful.
The smell could not be reproduced on the ground but the avionics blower fan was inhibited before the aircraft departed the following day on a re-positioning flight to London Gatwick. The smell returned when the crew initiated their descent and they donned their oxygen masks and declared a PAN.
Investigation by the operator did not identify the definitive source of the smell, although a number of components were replaced. These included the right brake master cylinder which was found to be leaking hydraulic oil. The aircraft has completed over 30 flights since the incident without recurrence.