Boeing 747 Freighters Vulnerable to Water-Related System Failures
A Boeing 747-433(BDSF) freighter aircraft, operated by One Air and registration G-ONEE, experienced a series of events that put it at risk on February 8, 2024. The incident occurred during a flight from London-Heathrow to Hong Kong with no cargo on board.
The investigation found that the loss of two alternating current buses (AC bus 1 and 4) was caused by water contamination in the Generator Control Units (GCU). This led to the disconnection of the heating for all Pitot tubes, resulting in unreliable speed indications due to ice buildup in the probe.
The aircraft landed safely at Amsterdam-Schiphol without any injuries or structural damage. The investigation revealed a chain of defects that allowed water to enter the Main Equipment Centre (MEC), including missing sealant at the access mat and cracked or missing waterproof tape on the floor.