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THE AVIATION INDUSTRY, like many other industries, has some unique traditions. Water salutes, for example, were historically initiated by airport fire services to celebrate special events such as an inaugural flight, final airline service, or the retirement of a respected pilot.
Typically, a water salute involves two or more fire vehicles, parked perpendicularly outside the taxiway, spraying a water jet in an arc above a taxiing aircraft. The spray pattern is adjusted to a high-velocity jet, to achieve the necessary spray height and distance.
Clearly, a water salute is a novel and riskfree celebration and cannot cause any harm, so what has this tradition to do with aircraft accident and incident investigation?
On 20 September 2018, an Airbus A320 arrived from Jeddah International Airport, Saudi Arabia, with two flight crewmembers, five cabin crewmembers and 119 passengers onboard. The flight and the landing were uneventful and the aircraft taxied to gate C58 as instructed.
After turning towards the terminal, two fire-fighting vehicles, which were located on either side of the taxiway, started spraying water to welcome the aircraft with a water salute in celebration of the Saudi Arabian National Day.
One of the fire-fighting vehicles experienced a problem in controlling the roof turret causing the high-pressure water jet to suddenly spray a jet of water upwards, then downwards, just as the aircraft passed underneath. The water jet struck the opening latch of the aircraft emergency exit hatch, causing the hatch to release and to fall into the cabin. This resulted in the deployment of the left overwing emergency slide ramp.
The flight crew were alerted to the opening of the left hand forward emergency hatch by the master warning system. The aircraft was stopped immediately and the engines were shutdown.
The crew believed that a passenger had opened the hatch from the inside and might be exiting the aircraft. However, this was not the case.
The aircraft was towed to the gate with the slide ramp attached, where the passengers disembarked normally from the forward left passenger door.
The opening of the over-wing emergency exit hatch into the cabin slightly injured a passenger seated in the window seat. The passenger received medical attention at the airport medical center and decided to continue the journey after being medically cleared.
The flight crew was not aware that a water salute had been arranged and therefore could not inform the cabin crew or passengers prior to the event.
The water salute was also unexpected, as the Saudi Arabia National Day was three days later.
SO WHY DID THIS HAPPEN?The A320 is equipped with four floor level type I emergency exits, which are the forward and aft passenger doors on the left side and the two service doors on the right side of the cabin. The aircraft is additionally fitted with four type III emergency exits on either side of the cabin at seat rows 35 and 36. These exits are called ‘hatches’ because they are not hinged and are designed to fall into the cabin, from where they are picked up and thrown outside by the passenger seated nearest to the hatch. Each emergency exit hatch weighs approximately 15 kg. Opening either of the passenger or service doors in the armed position automatically deploys a slide to assist evacuation. The opening of any of the overwing emergency hatches deploys a slide ramp over the trailing edge of the wing to provide the evacuee with a safe escape path. Similar to the passenger doors, the over-wing emergency hatches are only operational when the cabin pressure is equalized. They are accessible from the outside via the upper surface of the wing and are opened by applying a moderate force to a push panel. When the water jet struck the hatch push panel the hatch release mechanism operated and the hatch fell into the cabin. |
A320 (EMERGENCY EXIT) DOOR CONFIGURATION |
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As a result of the opening of the overwing emergency exit hatch, the slide ramp deployed and inflated as designed. An inspection of the slide ramp approximately one hour after the incident, identified that the slide deployment mechanism operated, the slide ramp deployed, and the slide remained inflated, as designed and certified. A company engineer inspected the emergency exit hatch and the airframe hatch attachments. No damage was found to the aircraft, and the emergency exit hatch was refitted. |
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WHY DID THE FIRE VEHICLE WATER JET STRIKE THE EMERGENCY EXIT LATCH?
The investigation focused on the firefighting vehicle and found that a failure in the operator’s hand controller, resulted in
an unresponsive, erratic turret movement, which sprayed the high-velocity water jet against the aircraft fuselage and the hatch release push panel.
HOW CAN THIS BE PREVENTED IN THE FUTURE?
The intent to carry out a water salute must be properly communicated in advance to all parties, including the flight crew. If the pilots feel confident that the water salute will not pose a threat, it may proceed.
This will prevent any confusion on the ground and onboard the aircraft, and the cabin crew can brief the passengers.
This briefing is critical, as unsuspecting passengers may panic and behave erratically, which could escalate to unsafe
passenger actions and pose a threat to the safety of those onboard.
The process of water salutes is not generally formalized by airlines, airport operators, or airport fire services. While water salutes are celebratory in nature, they are also non-normal practices with the potential for harm and damage. Therefore, airport operators, airlines and airport fire services need to have a risk assessment process in place to ensure that damage and injury can be avoided.
The correct functioning of fire vehicle water turrets is critical and not only in an emergency situation. Because, as this
incident has shown, they have the potential to cause injury, hinder fire-fighting or rescue activities, or cause damage to aircraft, or equipment. A routine “dry” turret check procedure was recommended to ensure that malfunctioning turrets are identified prior to their operation with water or foam.
WHAT CAN WE LEARN FROM THIS EVENT?
Even apparently benign events can cause unforeseen safety significant problems.
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Written by: Mr. Hans Meyer, Senior Air Accident Investigator, GCAA, UAE
Published on: The Investigator Magazine, Volume 1, Issue 12, July 2019