What happened
On 4 October 2023, an Airbus A321-253NX, registration G-OATW, was operating a commercial passenger flight from London Stansted to Orlando. Shortly after takeoff, passengers and crew noticed unusual noise and a drop in temperature within the cabin. A loadmaster identified that a window seal was flapping and a windowpane had shifted.
As the aircraft climbed, the situation deteriorated. While the aircraft's pressurization remained stable, the crew eventually decided to return to Stansted. Upon landing, a post-flight inspection revealed significant damage: two complete window assemblies were missing, a third window had a dislodged seal and pane, and a fourth window was protruding from the fuselage. Additionally, pieces of acrylic were found inside the left horizontal stabiliser, which had been punctured by debris.
The investigation
The AAIB investigation focused on the aircraft's activities the previous day, during which it had been used for a filming event. To simulate a sunrise, high-intensity halogen lights were positioned near the aircraft. The investigation found that six Maxibrute 12 lights, providing a combined 72,000 W, were used. These lights were positioned between 6 and 9 metres from the windows, which was closer than the manufacturer's recommended 10-metre minimum distance.
Examination of the damaged windows showed that the acrylic had shrunk and deformed. Specifically, some panes showed a reduction in size of up to 7%. The investigation also found melted foam on the cabin liners near the affected windows, confirming significant heat exposure. The investigation noted that the gaffer in charge of the lighting setup was unaware of the specific thermal limitations or the manufacturer's datasheet for the equipment.
Findings
- The primary cause of the damage was thermal deformation of the acrylic windowpanes caused by infrared energy from high-intensity halogen lights.
- The low thermal conductivity of the acrylic prevented heat from dissipating, leading to temperatures that caused the material to soften, shrink, and distort.
- The distorted window dimensions prevented the panes from maintaining an effective seal, allowing them to be dislodged by airflow and pressure changes during flight.
- The risk assessment for the filming activity focused on personnel safety rather than the potential for technical damage to the aircraft structure.
- Knowledge of similar previous occurrences involving high-intensity lights and window damage was not widely shared within the aviation community.