What happened
On 11 September 2008, a Boeing 737-800, registration EI-DYD, was performing a scheduled public transport flight from Dublin to Stansted. During the takeoff roll from Runway 28, the aircraft experienced a physical impact that the crew initially perceived as a bump. While the aircraft continued its climb, the crew was initially uncertain of the cause of the impact.
As the aircraft reached Flight Level 120, the commander attempted to assess the situation. After a period of assessment, the commander concluded that a tailstrike had likely occurred. Following the established 'Tailstrike on Take and Off' checklist, the crew opened the pressurization outflow valve. Because the aircraft was already pressurized at this altitude, this action caused an immediate loss of cabin pressure.
The sudden depressurization triggered the cabin altitude warning horn. Because the aircraft was below 14,000 feet, the passenger oxygen masks did not deploy automatically. The flight crew had to manually deploy the oxygen system. During the descent back to Dublin, the cabin crew reported that some oxygen masks had failed to drop from their overhead units. The aircraft declared an emergency and returned to Dublin Airport, landing safely without injuries to the 148 passengers or 6 crew members.
The investigation
The AAIU investigation focused on the sequence of events leading to the loss of pressure and the technical state of the aircraft. Investigators examined the tail skid assembly, finding only superficial scoring on the shoe and noting that the green indicator band remained visible, signifying a low-severity strike.
Regarding the passenger oxygen system, the investigation found that while three Passenger Service Units (PSUs) initially failed to deploy masks, the issue was resolved when the crew re-activated the oxygen switch on the ground. The manufacturer had previously noted similar isolated incidents involving improperly stowed masks. The investigation also reviewed crew interviews, noting that the cabin service supervisor played a vital role in alerting the flight deck to the decompression.