What happened
On 17 January 2012, a Boeing 747-4B5F, registration HL-7601, was performing a commercial cargo flight from Chicago O’Hare International Airport to Brussels National Airport. The aircraft was transporting 390 cows on its main deck. While cruising at flight level 340 over the Irish Sea, the crew received a fire warning indicating a fire in the aft cargo compartment.
In response to the alert, the crew donned oxygen masks and initiated a controlled descent to a lower altitude. One crew member inspected the main deck but observed no visible signs of smoke or fire. Following the descent, the aircraft proceeded to London Heathrow Airport, where it landed without further incident. Emergency responders met the aircraft on the ground but found no evidence of fire or smoke damage.
The investigation
The investigation examined the circumstances surrounding the fire warning and the subsequent emergency procedures. The crew initially suspected that the warning might have been erroneous. The investigation considered the environmental conditions within the cargo hold, specifically noting that the transport of live cattle likely resulted in higher-than-normal humidity levels within the main deck compartment.