Photo: Shutterstock AI A cargo door left open during a rainy night led to a chain of serious malfunctions on a Boeing 747, causing it to dive at more than 6,000 feet per minute and prompting an emergency declaration in the air, according to the official investigation report from the British Air Accidents Investigation Branch (AAIB).
The incident occurred on February 8, 2024, but the full investigation report was published in September 2026 and is now included in the Authority's new monthly newsletter. Only five crew members were on board, and none were injured. There was no reported damage to the aircraft.
The plane was a Boeing 747-433 cargo plane scheduled to fly from London Heathrow Airport to Hong Kong. The plane took off empty, weighing approximately 299 tons.
The night before the flight, the technical crew performed maintenance on the aircraft, during which they had to exit and re-enter the aircraft several times. As a result, the front left L1 door was left open overnight.
In the two hours before the work was completed, approximately 4.6 mm of rain fell in the area, and the wind blew toward the open door. When the flight crew boarded the aircraft, they noticed water on the carpet near the door and on some of the floorboards.
Despite this, the flight took off. According to the report, the first error message appeared after the plane had already exceeded the decision speed during the takeoff run, a stage at which takeoff would normally continue.
During the climb, numerous fault messages related to the electrical system began to appear in the cockpit. The autothrottle system disconnected, and some of the autopilot's navigation modes stopped functioning.
A few minutes later, the plane also lost power to another channel. The crew reset one of the systems several times, but it disconnected again and was finally left without power.
The loss of both power channels caused other systems to shut down, including pitot tube heating, which is used to measure the plane's speed. Without heating, the sensors could freeze in freezing conditions and give pilots incorrect speed data.
The crew initially declared a PAN and began exploring alternative landing options. After receiving information on weather conditions at various airports, the crew decided to divert to Schiphol Airport in Amsterdam, which had long runways and relatively favorable conditions.
However, during the flight, a decompression problem also developed. The cabin altitude began to rise, and the crew had to begin descending to avoid using oxygen masks.
As the plane descended through an altitude of about 12,000 feet, it entered stall conditions. The three airspeed indicators began to show a sharp and erroneous decrease in the plane's speed after the pitot sensors froze.
The autopilot remained engaged and attempted to return the aircraft to the selected speed by lowering the nose. The aircraft's pitch angle reached 7.6 degrees downward, and the rate of descent jumped to approximately 6,240 feet per minute.
As the plane emerged from the bald layer, the sensors disengaged and the airspeed reading jumped by about 85 knots in four seconds. The speed peaked at 383 knots, triggering an overspeed alert that lasted 55 seconds.
At this point, the crew declared a MAYDAY. After the plane emerged from the clouds, the speed data became reliable again and it continued on its way to Amsterdam.
During landing preparations, the crew also received an alert about a flap malfunction. The crew recalculated the landing distance and was required to land at a higher speed than usual.
The flight controllers gave the crew additional time to complete the checks and directed the aircraft to runway 06 at Schiphol Airport. The landing was completed safely, and the aircraft taxied to the parking stand, where maintenance crews were waiting for it.
The investigation determined that water entering through the cargo door area reached the generator control units, located in the main equipment center below the cargo deck floor. The water intrusion disconnected two power lines and disabled several vital systems.
The investigators could not determine the exact route the water took from the floor to the control units, but identified several weaknesses in the protection against water ingress.
The report also found other incidents of water ingress into electrical and electronic systems in this area on 747-400 aircraft in the past. Following the investigation, the AAIB issued four safety recommendations to strengthen inspection and maintenance requirements for waterproofing and protection measures.
The report defines the event as a "serious incident" and highlights the chain of events that arose from a malfunction that initially seemed relatively simple: a door left open during a downpour.