Turbulence alone, or turbulence followed by other misjudged actions, can kill. Oh yes, it CAN bring down an airliner.
Let’s see a story of a near-crash that started with entry into turbulence. Seeing, or reading, is believing; not someone’s wishful thinking.
Air travel has its risks. We accept those risks, and fly. We used to apply the same logic to travel by ship. Tell any airline to sell you a ticket on a guaranteed accident-free flight. They will show you the door.
This was a Boeing 747SP (a shorter, faster, baby jumbo jet) on a flight from Taipei to Los Angeles International Airport. Ten hours into the flight, about 300 nautical miles from destination while in cruise at 41,000 feet it flew through severe clear air turbulence. This resulted in a loss of power from number four engine (the outboard, starboard engine); despite the efforts of the flight engineer, engine four eventually flamed out.
Although the crew began procedures to relight the engine, they did it well above Boeing’s recommended maximum altitude of 30,000 feet. A lack of rudder input meant the crew were not doing enough to correct the yaw caused by drag from the dead engine; although the autopilot was making corrective actions, the autopilot installed in 747s at the time only controlled the ailerons (which control roll, or bank) and not the rudder (which controls yaw). Both were needed to effectively counteract the extra drag, and in the absence of this the aircraft began gradually rolling to starboard.
The drag on the aircraft was also reducing its airspeed, and adjusting the autopilot for a shallow dive did not improve matters, so the captain disengaged the autopilot to increase airspeed manually. Unfortunately at the time the autopilot was applying maximum port aileron to counteract the drag from the dead starboard engine; the crew should have matched this with their manual controls when disengaging the autopilot but didn’t, so the roll continued at a higher rate. The NTSB said in its report that the captain was focused almost exclusively on the airspeed problems at this point, and the aircraft was in cloud so there were no visual references to what the aircraft was doing.
After about 30 seconds the aircraft made a wing-over and rolled completely, descending rapidly at up to 60° down-angle and losing about 30,000 feet in less than two minutes. Speeds exceeded the airframe’s maximum mach number of 0.92 (92% of the speed of sound) on two occasions, and strong gee forces were felt for several minutes, up to a maximum of about five gees. About ten feet of the port tailplane and five feet of the starboard, including large parts of the elevators, were ripped off by aerodynamic forces during the descent, and during the periods of high gee the inboard main landing gear was forced down which also resulted in several of the landing gear doors falling off. There was sundry other damage to the empennage area and the landing gear bays.
At 11,000 feet the aircraft broke through the clouds allowing the captain to get visual references, and finally stabilise at about 8,500 feet, after which engine four was successfully relit. With part of the landing gear down and one of the hydraulic systems empty, it was impossible to reach LAX with the increased drag, so the captain diverted to San Francisco International Airport and made an emergency landing. There were several injuries caused by the high-gee portion of the incident but no fatalities.
The NTSB concluded that the incident was caused by “the captain’s preoccupation with an inflight malfunction and his failure to monitor properly the airplane’s flight instruments which resulted in his losing control of the airplane.”
Although the 747 was severely damaged by the incident—including the wings being permanently bent upwards—it was repaired and returned to service.
Author – Krishna Kumar Subramanian
