Incident Overview
On 17 January 2012, a Boeing 747-4B5F freighter, registration HL-7601, was operating a commercial cargo flight from Chicago O'Hare Airport to Brussels National Airport. The aircraft was cruising at Flight Level 340 over the Irish Sea when the flight crew received a fire warning for the main deck cargo compartment. The main deck was carrying 390 head of cattle.
Crew Actions
Upon receiving the warning, a crew member proceeded to the main deck to investigate but observed no evidence of smoke or fire. Suspecting the alert might be false, the crew nonetheless decided to follow the Quick Reference Handbook procedure for 'Main Deck Cargo Compartment Suppression'. This procedure required donning oxygen masks, initiating a controlled cabin depressurisation, and commencing a rapid descent.
Landing and Aftermath
The crew descended and subsequently made an uneventful landing at London Heathrow Airport. Emergency services met the aircraft upon arrival but found no indications of smoke or fire.
Pilot's Assessment
The commander, holding an Airline Transport Pilot's Licence with 16,231 total flying hours (7,312 on type), believed that the high humidity levels resulting from the presence of the cattle on the main deck were the cause of the fire warning.
Damage and Injuries
There was no damage to the aircraft and no injuries to the three crew members on board. Passengers were not carried on this cargo flight.