During taxi for take-off, the crew of the BAe146-100 aircraft noticed a 'yellow' hydraulic system 'low quantity' warning light on the aircraft's master warning system panel.
At approximately the same time, a cabin crewmember opened the flight deck door to alert the flight crew to the presence of fumes in the cabin. Passengers and two off-duty cabin crew reported a slowly moving white haze, low on the right side of the passenger cabin, in the vicinity of row 6. The haze was acrid and transparent and caused coughing and breathing difficulties.
An off-duty cabin crewmember also went to the flight deck and told the captain that the situation in the cabin had worsened, that there was smoke on the right side of the cabin and that passengers were having difficulty breathing. Because of the urgency of the report the pilot stopped the aircraft on a taxiway and instructed the cabin crew to prepare to evacuate passengers through the left doors. After shutdown procedures were completed, he ordered the evacuation.
The two operating cabin crewmembers opened the forward and rear left doors and deployed the escape slides. The two off-duty cabin crewmembers evacuated first, one through each door, to assist passengers at the base of the slides.
A passenger reported that cabin crew who stood at the aircraft doors to control the evacuation and block access to the right doors were out of view of the cabin. Therefore, the cabin crew could not see other passengers attempt to retrieve cabin baggage; an action that clogged the aisle and slowed progress to the exits. However, cabin crewmembers reported that cabin baggage did not delay the evacuation.
A cabin crewmember at the base of a slide reported that early in the evacuation, some passengers struck others that had not yet cleared the slide. Some fell as they reached the slide base and she lifted people to avoid a bank-up and the possibility of injury. Later, the evacuation proceeded in a more orderly manner. Cabin crew reported that they did not request assistance from able-bodied passengers during the evacuation.
Medical assistance
The airport Rescue Fire Fighting Services attended shortly after the evacuation was completed. They offered medical assistance and administered oxygen to two passengers. Medical assistance was also offered to passengers and crew on arrival at the airport terminal. None of the passengers requested medical attention.
Aircraft crew actions
Company emergency procedures required flight crew to don oxygen masks at any time that smoke or fumes were detected in the cabin. The procedures also required the flight deck door to remain closed to avoid flight crew incapacitation from fumes.
Both the pilot and the cabin crewmember that opened the door to speak to the flight crew reported that they were aware of the emergency procedure requirements. However, the pilot reported that the flight crew did not don oxygen masks as there were no fumes in the area and because the urgency of the cabin crew messages conveyed the need for an immediate evacuation. The cabin crewmember reported that it was quicker to open the flight deck door and safe to do so as there were no fumes in the area.
Cabin crew who had inhaled vapours, or who had assisted passengers off the escape slide, reported that during the continued tour of duty they suffered effects that included extreme tiredness, sore muscles and minor throat and chest problems.
Hydraulic system
Two independent systems provided hydraulic power to the aircraft flight controls and landing gear. These hydraulic systems were designated 'green' (left) and 'yellow' (right).
The power generation components were housed in the hydraulic bay, situated immediately forward of the main landing gear bay, below the forward rows in the passenger cabin. A light on the flight deck instrument panel provided a low hydraulic quantity warning when the fluid level fell below the operating level.
An inspection by the operator found that a leak in a hydraulic coupling allowed fluid under pressure to escape as vapour into the hydraulic bay and enter the passenger cabin via gaps in the sidewall lining. The 'o' ring seal for the coupling was replaced and the leak stopped. After a number of subsequent flights the coupling leak re-occurred. On closer inspection it was found that the coupling had a crack along its threads. The coupling was replaced.
The company reported that a subsequent Non Destructive Test (NDT) examination of the cracked coupling revealed that the coupling had failed through the bottom of a thread due to overload, which was consistent with having been done up too tightly.
Hydraulic equipment bay sealing
The aircraft manufacturer had generated three service bulletins that either required or recommended remedial action to improve sealing between the hydraulic bay and the passenger cabin. A zonal inspection was also conducted in the area at regular intervals.
At the time of the occurrence the operator had incorporated the first two service bulletins and had scheduled, but had not commenced, the third.