Jumbo Jet - Gross Jet Upset

This phenomenon affects all commercial aircraft, including the Boeing 747 "jumbo". When the aircraft does fall below its stall speed while cruising, the aircraft is liable to be affected by what used to be called "gross jet upset", and stalls and descends uncontrollably.

In fact, this has happened to a jumbo jet. It happened in February 1985 to a Boeing 747SP operated by Taiwan's China Airlines while the aircraft was cruising at FL410 (41,000 feet) over the Pacific. I recall reading that there was only about a 10-knot difference between the maximum cruise speed and the aircraft's stall speed at that altitude, at that weight.

The 747SP -- a shortened version of the 747 built in the 1970s and early 1980s to offer more range than the standard-body version of the time -- rolled over rapidly to the right and plunged some 30,000 feet in a very steep dive after one engine flamed out and the pilot in control switched off the autopilot. (The pilot in control was blamed for not inputting enough left rudder after disconnecting the autopilot. The left rudder input was required to counter the asymmetrical thrust from the three remaining engines.)

The three engines did not have enough power to maintain the aircraft at a speed above stall speed at that altitude, a factor that no doubt helped induce the very steep dive. However, because modern commercial jets are designed to withstand stresses far beyond those they are ever expected actually to encounter, the 747SP did not break up and the pilots were able to recover control at an altitude below 11,000 feet. It limped into San Francisco with major structural damage and two people onboard seriously injured.

Note from the article above that the condition of the debris found suggests that the Air France A330 which crashed in the Atlantic did not actually break up in the air, but only when it hit the water. Had the aircraft not been flying at night