A Boeing 747-433 freighter, registration G-ONEE, encountered multiple electrical problems and unreliable airspeed shortly after taking off from London Heathrow Airport on 8 February 2024. The flight, bound for Hong Kong International Airport, was forced to divert and land safely at Amsterdam Schiphol Airport.
The Air Accidents Investigation Branch (AAIB) report, published today, states that water entered the main cargo deck before departure because the L1 door was left open during rain. This water ingress led to the loss of two AC electrical buses, causing numerous system failure messages and the loss of all pitot tube heating.
While attempting to divert, the aircraft entered icing conditions, freezing the pitot tubes and causing all three airspeed indicators to show erroneously low readings. The autopilot pitched the aircraft nose-down to regain indicated airspeed, resulting in a 6,240 ft/min descent rate before correct airspeed was regained.
The investigation found weaknesses in water ingress protection measures and noted previous similar events on 747-400 aircraft. The AAIB has made four safety recommendations to address maintenance concerns regarding repetitive inspections of drip shields, floor panel seals, waterproof tape, power drive units, and the L1 door floor mat.