Saudia HZ-AS55

An uneventful arrival from Jeddah

Saudia Airlines flight SV566 landed at Dubai International Airport at 10:38 local time on 20 September 2018. The flight from Jeddah King Abdulaziz International Airport had been uneventful. The Airbus A320-214, registered HZ-AS55, carried 119 passengers, two pilots and five cabin crewmembers. After landing, the pilots followed instructions to taxi towards gate C58.

The aircraft had been delivered to Saudia in 2017 and had accumulated 4,977 flight hours and 3,933 landings. Its cabin contained 12 business-class and 132 economy-class seats. AAIS found that it was airworthy before the incident and that it had been certificated, equipped and maintained in accordance with the applicable requirements. Both flight crewmembers held appropriate licences and valid aviation medical certificates.

Dubai Airports Aviation Business Development had requested a water salute to celebrate Saudi Arabia National Day. The request reached the Airport Fire Services Operation Center and the airline operations manager. It did not reach the pilots or the ground handlers waiting at the gate. The national day itself was three days later, on 23 September.

An uncontrolled jet opens the hatch

After the aircraft turned towards the terminal, two firefighting vehicles began spraying water from opposite sides of the taxiway. Their turret operators selected forceful jets to form a far-reaching arc above the aircraft. The vehicle on the left, FIRE 8, was a Rosenbauer Panther 8X8. Its roof turret stopped following commands from the operator's hand controller.

As HZ-AS55 passed beneath the water, FIRE 8's high-pressure jet moved upwards and then downwards. It struck the left forward over-wing emergency exit. AAIS found that the jet's high kinetic energy pushed the external opening panel inwards. The hatch opened, fell into the cabin and caused the left over-wing emergency slide ramp to deploy.

The passenger in the adjacent window seat sustained minor injuries from the falling hatch. A warning alerted the flight crew that the exit had opened. The pilots initially suspected that a passenger had operated it from inside. They immediately stopped the aircraft, applied the parking brake and shut down both engines to protect anyone who might be leaving the cabin. The external cause became apparent later.

The aircraft was towed to the gate with the inflated slide ramp still attached. Passengers disembarked normally. The injured passenger received medical attention, was medically cleared and chose to continue the journey. AAIS found no aircraft damage, and the summary also records no damage to property or the environment.

The exit and slide operated as designed

HZ-AS55 had four floor-level Type I emergency exit doors and four Type III over-wing emergency exit hatches. The over-wing exits were at rows 35 and 36. Opening an over-wing hatch activated a slide ramp over the trailing edge of the wing to help occupants leave the aircraft.

The Type III exits were always considered armed during aircraft operations. Their opening mechanism became operational when cabin pressure was equalized, and the installation prevented opening while the cabin was pressurized. From inside, a person could remove a cover and pull a handle. From outside, the exit could be reached from the upper wing surface and opened by pressing a red panel.

Each hatch weighed approximately 15 kg. The hatches were unhinged and opened inwards, after which the person beside the exit was expected to pick up the hatch and throw it outside. The investigation noted the value of an exit that an untrained person could open from outside during an emergency. It was unable to identify another similar occurrence in which these exits had opened unexpectedly.

An inspection approximately an hour after the incident confirmed that the slide deployment mechanism had activated and that the ramp remained inflated as designed. An airline engineer inspected the emergency hatch, its airframe attachments and its mechanism, found no damage, and refitted the hatch. After investigators had collected the relevant evidence, the inflated ramp was detached.

Repairing FIRE 8 and authorizing another flight

FIRE 8 was removed from service after the event. The vehicle manufacturer sent a maintenance team to examine and repair the turret, with an AAIS investigator attending. The work traced the loss of vertical turret control to a fault in the elevation control potentiometer on the hand controller. The potentiometer was replaced and the turret movement recalibrated before the vehicle returned to service.

The manufacturer said that no similar turret control problems had previously been reported. Maintenance records for the airport fleet contained no similar problem in the preceding 12 months. However, maintenance technicians told investigators that they had seen similar movements before and had corrected them by recalibrating the turret and hand-controller movements. AAIS considered that the failure to follow controller commands appeared to have occurred before this incident.

Saudia's Technical Services department issued Engineering Authorization S25-A10024 for one flight with the left over-wing slide ramp removed. It required an inspection under the aircraft maintenance manual procedure, securing the hatch during flight, and informing every crewmember that the ramp was inoperative and unavailable for an emergency.

The authorization also required rows 33 to 44 to be blocked and identified. This reduced the permitted passenger seating capacity from 144 to 72. The aircraft departed Dubai at 16:22 local time as a commercial flight following what the summary describes as a four-hour delay.

Findings and safety recommendations

AAIS concluded that erratic directional movement of the water jet onto the external push panel caused the hatch to open and fall into the cabin. It identified two contributing factors: the failed potentiometer that controlled the roof turret, and the airport fire service's failure to formally describe and risk-assess the water-salute process. The possibility of erratic turret movement had therefore gone unidentified.

The investigation also examined communication. Because the pilots had received no warning of the salute, they could not prepare the cabin crew or passengers. Cabin crewmembers became concerned when they saw the fire vehicles spraying the aircraft. The passengers' reaction was unknown. AAIS found that the pilots followed known procedures using the information available to them when confronted with the unexpected events.

AAIS issued two safety recommendations to the UAE General Civil Aviation Authority for aerodromes allowing water salutes. SR07/2019 called for a formal risk assessment and a procedure to mitigate identified risks. SR08/2019 called for a routine dry turret check to identify malfunctioning equipment during maintenance or before operation with water or foam.

The investigation connected reliable turret control with firefighting and rescue capability as well as ceremonial spraying. Its analysis described the potential for a controller fault to injure people, damage aircraft or equipment, and hinder emergency operations. Checking turret movement before spraying would allow operators to detect a failure to follow hand-controller inputs.