During taxi from the terminal, when the British Aerospace BAe 146-100 was approximately 150 metres from the parking bay, and while making the pre-flight safety public address, a flight attendant began coughing due to a slight irritation in her throat and was unable to finish the presentation. When the second flight attendant went to the front of the cabin to assist, she too developed a cough. Both flight attendants saw what they described as a grey, smoky gas in the airstair region of the left door.
At approximately the same time, the first officer experienced an involuntary cough and stinging eyes and donned an oxygen mask. A short time later a flight attendant opened the flight deck door and advised the flight crew that smoke, or fumes, were filling the forward section of the passenger cabin. The flight crew turned off both air conditioning packs and the Auxillary Power Unit and immediately returned to the parking bay after advising Air Traffic Control and the ground handling company. During the return to the bay, the captain opened the left flight deck window and the flight attendants moved the forward seated passengers to the rear cabin and instructed passengers to cover their nose and mouth.
When the flight crew reported their intention to return to the terminal, the ground handling company requested that passengers remain on board the aircraft at the terminal. The first officer advised the company that this was not possible as there were fumes in the cabin. The aircraft arrived back at the parking bay approximately four minutes after the fumes were first noticed.
Upon arrival at the terminal the captain instructed the flight attendants to open the doors. A flight attendant returned to the front of the aircraft from the rear cabin and opened the forward left door. The second flight attendant opened the rear left door. The flight attendants reported that there were no portable stairs available when the doors were opened. The forward flight attendant called to ground staff in the area and portable stairs were brought to the forward left door. The flight attendants elected not to attempt airstair activation as that was believed to be the source of the smoky gas.
To avoid delay, flight attendants disembarked passengers through the forward door, in the vicinity of the fumes. They reported that, as they were coughing, they could not speak to passengers during the disembarkation.
The company later reported that the urgency of the situation might not have been conveyed to ground services during the initial advice of the aircraft's return to the terminal.
After passengers had disembarked, Aviation Rescue Fire Fighting (ARFF) personnel advised the flight attendants to sit outside the aircraft for ten minutes. The flight attendants later underwent a medical check at the recommendation of the company. Neither the captain nor first officer sought medical attention following the incident. All crewmembers have since returned to duty.
Some passengers later reported that they experienced coughing, watering of the eyes, and respiratory irritation during the event. They also reported that medical attention was not available at the terminal. The ground handling company reported that when passengers reached the terminal, staff did not call a doctor when requested by passengers. They also reported that ARFF personnel had recommended that passengers go outside into the fresh air but few passengers had followed that advice.
Subsequent investigation revealed that neither the operator nor the ground handling company had emergency response procedures in place to cover the situation of an aircraft emergency return to the terminal from a taxi position.
The aircraft was fitted with an integral stairway (airstair) at the forward left door. However, portable stairs were often used in place of the narrow integral stairs for convenience and ease of boarding.
The operator reported that the forward door airstair had been in use before the flight but had been retracted and replaced by portable stairs prior to boarding passengers.
The airstair was operated from inside the aircraft. It was extended manually, but retracted by hydraulic pressure when the airstair-selector `retract' switch was pressed and held in position. This procedure allowed hydraulic fluid (Skydrol) to pass under pressure through a series of lines and valves to activate airstair retraction. When the airstair was retracted, and the airstair-selector switch was released, the rocker-type switch was designed to spring back to the `off' position. The airstair was then pushed along tracks to a rearward, stowed position out of the doorway.
While the aircraft was on the ground with engines off, an electric stand-by pump was used to top-up and maintain pressure for airstair retraction. After engine start-up, engine driven pumps delivered pressure to the airstair hydraulic system.
An examination of the integral airstair by company engineers revealed that the airstair selector switch had stuck in the `retract' position, and also revealed a failed `o' ring in the retraction jack `banjo' fitting in the airstair actuator. During the examination, other `o' rings had also shown signs of deterioration.
The operator reported that an internal failure caused the switch to be stuck in the `retract' position and also noted that the switch was flush with the surrounding panel. The operator considered it possible that the body of the switch became fouled on the panel and remained in the `retract' position.
The operator also reported that the aircraft maintenance manual stated that the airstair `retract' switch should have had a hinged flap cover. The flap was missing and an engineering order had not been raised for its removal.
Crew emergency procedures and manuals
Flight crew emergency procedures for smoke or fumes required flight deck crew to don oxygen at any time that smoke or fumes were evident. The captain reported that he did not don the oxygen mask when he was alerted to the presence of smoke or fumes as the fumes did not affect him. He also considered it more important to return the aircraft to the parking bay to disembark passengers than to stop and don his oxygen mask.
Flight crew emergency procedures for smoke or fumes also required that the flight deck door remain closed. However, this procedure was not reflected in the flight attendant emergency procedures manual. The flight attendants were unaware of the requirement to keep the flight deck door closed.
The electric stand-by pump would have been switched off from the flight deck shortly after airstair retraction, thereby reducing hydraulic pressure even though the retract switch was stuck in the `on' position.
However, after engine start, the engine driven hydraulic pumps would have delivered pressure to the airstair hydraulic system. Sustained hydraulic system pressure would then have been delivered to the airstair retraction system when the pump was engaged.
The failure of the retract switch allowed sustained pressure to be delivered over an undetermined, but excessive time, to the airstair retraction system. That exposure resulted in the failure of the `o' ring and consequent leakage of fluid, as a fine mist, into the cabin.
Instead of using the crew interphone, to contact the flight crew, the flight attendants followed common practice and opened the flight deck door to tell the flight crew about the fumes. This action exposed the flight crew to the fumes.
The captain's decision not to don his oxygen mask could have resulted in flight crew incapacitation through exposure to smoke or fumes.
The information exchange between the flight crew and ground staff should have indicated a need for portable stairs at the rear door. The decision to disembark the passengers through the forward door was not appropriate. Use of the rear door would have provided passengers and flight attendants better protection from the fumes.
The absence of suitable emergency ground procedures, delay in response from ground staff, and the provision of stairs to only the front door, increased the exposure to fumes for passengers and crew.
- The airstair retract switch remained in the `on' position, thereby allowing sustained hydraulic pressure to be delivered to the airstair retraction system.
- The airstair actuator banjo fitting `o' ring failed.
- The non-use of the crew interphone system exposed the flight crew to the fumes.
- Cabin crew opened the flight deck door allowing the mist/fumes into the flight deck.
- Emergency response teams did not provide portable stairs in a timely manner.
- Cabin crew disembarked passengers through the fumes affected forward left door.
Local safety action
As a result of the investigation the operator has:
- Scheduled detailed visual inspection of airstair actuators and fittings during routine maintenance.
- Issued maintenance instructions to check that:
- airstair retract switch covers are fitted and correctly aligned with the rocker switch;
- adequate tolerances exist when replacing panels around the retract switch so that the switch cannot be fouled by surrounding panels; and
- the retract switch operates without obstruction and springs back to the `off' position.
- Amended maintenance schedules to include:
- Operational check of the airstair hydraulic system;
- Inspection for evidence of hydraulic leakage from the `retract' actuator banjo fittings and airstair hydraulic coupling and banjo fitting; and
- Regular change of airstair banjo fitting `o' rings, as required, during heavy maintenance checks.
- Amended flight attendant emergency procedure manuals and training sessions to reflect the requirement for cockpit doors to be closed in the event of smoke or fumes.
- Amended flight crew and flight attendant training modules to include scenarios that reflect aspects of this occurrence, including information regarding suitable evacuation paths for passengers and crew.
- Formed a working group within the Australasian Aviation Ground Safety Council. The working group will develop a Recommended Industry Practice procedure for response to an aircraft that has an emergency return to the terminal from a taxi position
|Date:||24 May 2001||Investigation status:||Completed|
|Time:||0555 hours WST|
|State:||Western Australia||Occurrence type:||Fumes|
|Release date:||18 September 2002||Occurrence class:||Operational|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||British Aerospace PLC|
|Aircraft model||BAe 146|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Perth, WA|
|Destination||Barrow Island, WA|