Aircraft Upset - Jet Upset

The phrase jet upset refers to past accidents (some crashed and some recovered, usually with significant damage to the structure), where a jet airliner was "upset" and went into a high dive. That phenomenon was almost unknown in the days of piston-driven propeller airliners, which is why those accidents were referenced as "jet" upsets: because it was a repeated phenomenon that was unique to jet airliners, with swept-back wings, jet engines and movable horizontal stabilizers, none of which were found on the piston/propeller airliners. With the phasing out of piston-driven propeller airliners, that phrase has gradually given way to "loss of control," which includes, but is not limited to, the upset/high-dive type of accidents. The term jet upset was most heavily used in the 1960s and 1970s as the phenomenon was not well understood and was still being researched. Contemporary authors tend to group the phenomenon under loss of control.

There have been a variety of causes and contributing factors, in past jet upset accidents:

• February, 1959: A Pan American B-707 Clipper Washington N712PA upset and went into a high dive while cruising over the Atlantic at flight level 350. Control was not recovered until reaching 6,000 ft. After landing safely at Gander, extensive structural damage was found, but there were only a few minor injuries. The Captain was in the cabin when the autopilot disconnected without adequate warning to the First Officer, who was distracted with a "howgozit" report form. It wasn't until the first officer felt the stall buffet that he realized they were descending rapidly and about to turn upside down. He was unable to level the wings. Fortunately, the Captain was able to return to the cockpit strap into his seat while enduring significant G-forces. He took over the controls, leveled the wings and pulled out of the dive.

• February, 1963: Northwest Orient Airlines Flight 705 - A Northwest Airlines B-720B was hit with a powerful updraft (it suddenly began climbing at 9,000 ft. per minute) while climbing through 17,000 ft as it tried to fly between thunderstorms shortly after takeoff. The nose pitched up so high that the pilot reacted by using full nose-down trim on the horizontal stabilizer (HS), while simultaneously pushing the elevators to the full down position. Then, an equally powerful down draft hit the plane and it went straight down in a matter of seconds. The pilot then pulled back on the yoke, moving the elevators to the full up position. This imposed high G-load on the plane, resulting in binding of the horizontal stabilizer jackscrew, such that it remained in a full trimmed down position. The plane came apart in the air, before hitting the ground.

• July, 1963: A United Airlines B-720, while climbing through FL 370, upset and dove until recovery at 14,000 ft. The plane encountered severe turbulence, downdrafts and updrafts, which caused the plane to stall. The plane was approaching the coffin corner of its flight envelope, when the turbulence was encountered. After that near disaster, the stall and mach buffet margins were widened on all jet aircraft, to preclude a plane getting into that situation again, where severe turbulence narrows the "coffin alley" margins so instantly that the pilots do not have time to avoid a high altitude stall.

• November, 1963: Trans-Canada Air Lines Flight 831 - All 118 on board a Trans-Canada Airlines DC-8-54F were killed, when the plane crashed 5 minutes after takeoff near Montreal, leaving a crater in the ground. Impact speed was over 500 mph. They found the pitch trim compensator actuator was in the extended position and the horizontal stabilizer trim setting was at 1.65 to 2 degrees nosedown (both were improper positions, for that stage of flight). "The probable cause of this accident could not be determined with certainty. Certain possible causes which were put forward could not be ruled out: 1) Icing of the Pitot system; 2) Failure of the vertical gyro; 3) An unprogrammed and unnoticed extension of the pitch trim compensator."

• February, 1964: Eastern Air Lines Flight 304 - An Eastern Airlines DC-8 crashed into Lake Pontchartrain about 5 minutes after taking off from the New Orleans Moisant Airport. All 58 on board perished. The water was only 20 ft. deep, yet only 60% of the wreckage was recovered, because the breakup was so extensive. The flight data recorder tape was too damaged to help the analysis. Instead, they used the maintenance records of that plane, and of other DC-8s, to conclude that the pilots had trimmed the stabilizer to the full nose-down position, to counter the excessive nose-up attitude that, in turn, was caused by a malfunctioning pitch trim compensator that had extended too far. Once the upset occurred, it was not possible to trim the HS back to the nose-up position, because of the severe G-forces generated by their pulling back on the yoke after the upset.

• February, 1985: China Airlines Flight 006: The number 4 engine flamed out on a China Airlines 747SP, while cruising at FL 410 over the Pacific Ocean. The captain ordered an attempt to restart the engine, while remaining at flight level 410 and with the autopilot controlling the plane. The airspeed was declining (because the remaining 3 engines did not have enough power to remain at a safe airspeed at that altitude). When the captain finally disconnected the AP, he failed to use left rudder to counteract the asymmetrical thrust, and the plane rolled rapidly to the right and entered a high dive attitude. He was unable to recover from the dive until below 11,000 ft. when they emerged from the clouds. The plane exceeded the maximum operating airspeed (Vmo) twice, during the dive. After recovery, the plane landed safely at San Francisco. It suffered major structural damage and 2 occupants received serious injuries.