19th of February 1985

A Boeing 747SP-09 was en route from Tapei (Taiwan) to Los Angeles (California, USA) on this day in aviation history in 1985. Onboard 23 crew and 251 passengers, the flight had been uneventful and the aircraft was cruising at FL410, approximately 300 nautical miles northwest of San Francisco (California, USA). A cloud layer stretched out below the flight path of the aircraft with tops reaching 37.000 feet. The autopilot was engaged and set to maintain 0.85 Mach (254 Knots Indicated Airspeed) At approximately 10.13lt the aircraft was approaching waypoint "REDOO" when the crew observed the speed fluctuating between 0.84 Mach (251 KIAS) and 0.88 Mach (264 KIAS), with the PMS (Performance Management System) continuously adjusting the throttles to maintain the target cruise speed.

Damage to the aircraft tail section, as seen after landing in San Francisco (Source NTSB)

This hunting of the throttles continued for a short while when at one point the speed increased to 0.88 Mach and the throttles were fully retarded to idle, with aircraft decelerating. When the speed dropped to 0.84 Mach the throttles moved forward, all engines responded, except engine #4. This engine was unresponsive. The Flight Engineer manually moved the throttle back and forward, with no response from the engine. A short while later he reported that the #4 had flamed out, On request of the Captain the Flight Engineer initiated the required checklist, and checked the performance data for a 3 engine cruise. Although the altitude limit for the inflight start was 30.000 feet for the aircraft the Captain ordered an inflight restart attempt while at 41.000 feet.

Damage to the aircraft tail section, as seen after landing in San Francisco (Source NTSB)

. During the attempt to relight the #4 engine the speed decayed and the aircraft started to roll to the right, nosed over, and dropped out of the sky The crew had lost control and the aircraft was tumbling out of the sky. The aircraft entered the clouds and continued to drop, the crew only regained control at approximately 9500 feet.

Unbeknown to the crew the aircraft suffered major structural damage during the "descent" and recovery. FDR data analysis revealed that the maximum vertical acceleration forces recorded during the descent were 4.8Gs and 5.1Gs as the airplane descended through 30,552 feet and 19,083 feet 2 of the occupants received serious injuries during the upset and recovery. A diversion to San Francisco was initiated where a safe landing was made.

The aircraft attitude during the descend due to the loss of control (Source Public Domain)

The National Transportation Safety Board investigated the incident and the full report is available by clicking here. They concluded that the Captain's preoccupation with the engine failure caused him to no longer properly monitor the aircraft's instruments, and an over-reliance on the autopilot system, which resulted in the crew losing control of the aircraft.

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