What happened
On February 14, 2002, a World Airways McDonnell Douglas DC10-30, registration N 526MD, was descending toward Shannon Airport when the crew observed several cockpit warnings. The incident began approximately ten minutes before landing when a cargo smoke caution and the master caution light illuminated. As the crew initiated emergency checklists, the situation escalated with the activation of a No. 2 pneumatic manifold failure light, followed by multiple cargo smoke warnings and a cargo fire warning.
The flight crew, wearing oxygen masks and smoke goggles, requested an expedited approach. Upon landing on Runway 24, the aircraft was met by several sections of the Airport Fire Service. An emergency evacuation of the three crew members and two passengers was conducted via a rescue ladder at the front left door. There were no injuries during the event.
The investigation
The investigation focused on identifying the source of the smoke and the cause of the pneumatic manifold failure. While the smoke cleared after landing, subsequent fault-finding revealed that the smoke reappeared whenever the Auxiliary Power Unit (APU) was operated.
Technical analysis of the aircraft's hardware revealed that the air bleed duct from the No. 2 engine had ruptured. This rupture allowed high-pressure hot air to escape, which subsequently charred the surrounding insulation and released smoke into the cargo compartments. Laboratory testing of the titanium duct material showed that the metal had become brittle and significantly thinned.
Findings
The investigation established that the primary cause of the duct rupture was hydrogen embrittlement. This chemical degradation was triggered by the presence of decomposed hydraulic fluid on the exterior of the duct.
It is believed that during a previous maintenance or servicing period, hydraulic fluid escaped from an adjacent line and became trapped between the titanium duct and its insulation. The heat from the operating duct accelerated the decomposition of the phosphate ester fluid, which then etched the metal. This process reduced the duct wall thickness to only 40% of its original specification, eventually causing the material to fail under operating pressure.