A Delta Airlines flight, number 159, made an emergency return to the Detroit Metropolitan Wayne County Airport on May 21. The flight had left Detroit and was somewhere over Lake Michigan when a warning light came on in the cockpit, indicating that an external cargo door was open.
Such a condition potentially creates a serious problem for the aircraft, a Boeing 747-400, due to the fact that it is pressurized and flies at 30,000 to 40,000 feet. At this level, at external door being opened in the cargo hold would mean that the only thing keeping the cabin from catastrophically decompressing would be internal doors, which are not designed to be used as primary pressurization bulkheads.
The flight was forced to circle above Lake Michigan for approximately one hour, dumping fuel to get down to a safe landing weight. The aircraft took off from Detroit Metropolitan Wayne County Airport at nearly its maximum gross takeoff weight. In the 747-400, the maximum takeoff weight is considerably higher than the maximum safe landing weight. For this reason, the plane was forced to dump some 200,000 pounds of fuel.
While the plane is capable of landing at higher weights than the maximum safe landing weight, doing so entails a fairly dangerous maneuver. The aircraft would have to be landed with the flaps set at just 20 degrees. This is because, at maximum takeoff weight, the normal flap setting imposes too much drag on the wings. The aircraft simply does not have enough power to do anything but descend with the flaps extended to the normal 30 degrees for landing. One consequence of this is that the landing speed is dramatically increased. A speed of 160 knots, or 184 miles per hour would be needed to safely flare the 747 on landing. At this speed, it is quite possible that the aircraft would not be able to safely come to a complete stop, even on a 10,000 foot runway.
The fuel was successfully dumped and the plane landed without incident. Some passengers were understandably annoyed. However, the pilots were taking the necessary precautions and acting with professionalism. Anything that could even potentially endanger a flight is an unacceptable risk.
The aborted flight comes on the heels of Delta proclaiming that inconvenienced customers would be authorized to receive up to $10,000 in vouchers. The company stated that the passengers on flight 159 would be adequately compensated and put on a different flight.