Boeing 747History, variants & specifications

China Airlines 006, 19 February 1985

A 747SP lost an engine at 41,000 ft, rolled inverted-ward and fell 31,500 ft in under 2.5 minutes. It was recovered and landed with 24 injured.

On 19 February 1985, China Airlines Flight 006 — a Boeing 747SP, registration N4522V — lost control at 41,000 feet over the Pacific and fell 31,500 feet in under two and a half minutes.

It was recovered, and it landed. That it did so at all is the remarkable part.

How it started

The number 4 engine failed in the cruise. On a four-engined aircraft that is an inconvenience, not an emergency — but it produces asymmetric thrust, pulling the aircraft towards the dead engine, which the crew must counter with rudder.

The flight engineer attempted a restart but did not close the bleed valve as the checklist required. Meanwhile the captain became absorbed in the engine problem and in the decaying airspeed, and left the autopilot engaged.

That was the trap. The autopilot held the wings level using aileron alone, up to its authority limit — silently absorbing the yaw the captain should have been countering with rudder. It masked the developing problem until it ran out of authority, at which point the aircraft rolled sharply right.

The upset

The 747SP rolled past 60 degrees, entered a steep descent and fell into cloud, where the crew lost outside reference entirely. Passengers experienced up to 5g.

The captain regained control at about 9,500 feet.

What the airframe took

The damage found afterwards is the reason engineers still talk about this flight:

  • The wings were bent permanently upward by about two inches.
  • Landing gear doors were torn away.
  • Large outer sections of the horizontal stabiliser were ripped off.

The aircraft had been loaded far beyond anything it would meet in service, and it held together well enough to fly on and land at San Francisco. Of the 274 aboard, 24 were injured, two seriously — a fractured foot and a back strain.

This is what the structural margins demonstrated in testing — wings pulled to 150 percent of limit load — actually buy.

The NTSB finding

The Board concluded the captain was distracted first by evaluating the engine malfunction and then by the decaying airspeed, and that he over-relied on the autopilot, which concealed the approaching loss of control. He also failed to apply the rudder needed to counter the asymmetry.

Why it still gets taught

Like Korean Air Lines 007, this is an automation accident rather than a mechanical one. In both cases the autopilot did exactly what it was designed to do, and in doing so hid a developing problem from the people responsible for it.

The lesson — that automation can mask a deteriorating situation until it abruptly hands it back — shaped how modern flight decks annunciate what the automation is doing and when it is running out of authority.

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