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In August 1983, two minutes after takeoff from Anchorage, pilots engaged the autopilot in “heading” mode and set it directly to the Bethel waypoint. From the black box recordings it appears the inertial navigation system never engaged. This could be because the aircraft was either more than 7.5 miles off the flight route to additional selected waypoints or it was not sufficiently headed in that direction. As a result, the 747 stayed in “inertial navigation armed” mode as the system resorted to the last set “heading” mode as it waited for the required conditions and continued to drift off course.
That early 747 apparently lacked an indicator that the heading mode was the one that was active. (Most likely, the only indication was that the indicator light for the inertial navigation system was amber when it should have been green). The aircraft continued off course and overflew the Soviet Kamchatka Peninsula, which juts into the Bering Sea, then headed straight toward a submarine base. Because of darkness the crew could not see this happening.
MiG fighters were scrambled and chased the 747 for a time, but turned back. By then the aircraft had drifted well off path and soon was over the Soviet territory of Sakhalin Island, where two more MiG fighters were dispatched. They misidentified the aircraft as a U.S. Air Force RC-135, essentially the same as a 747. The Korean aircraft was not on an emergency radio frequency. It was initiating communication with Tokyo, and it did not pick up any Soviet Air Force warning. At that moment Tokyo gave the instruction to climb. This was interpreted by the pursuing Soviet pilot as an evasive maneuver. The MiG pilot was instructed to shoot and did so (Degani, 2004).
2.2China Airlines 747 Engine Malfunction Near California (over-reliance on autopilot after fatiguing flight)
In February 1985, toward the end of a fatiguing flight from Taipei, the 747-SP lost the rightmost engine and began a right roll due to asymmetric thrust. The autopilot countered by trying to roll left. Since the pilot was hands off in trying to diagnose the cause, he did not notice the only indications of the autopilot effort: the control wheel left rotation, as well as a side slip and a reduction in speed. After some delay the pilot switched the autopilot from FMS to pitch-hold mode but still saw no indication that the autopilot was at its limit in trying to correct the rotation. The aircraft pitched down, the right wing finally dropped, and eventually the pilot switched to manual. The pilot was able to regain control at 9,500 feet (ft) and land safely at San Francisco. The event was attributed to fatigue and boredom at the end of a long flight, forgotten training that indicated manual takeover in such an event, and a lack of instrument indications (Degani, 2004).
2.3Simmons Airlines ATR-72 Crash Near Chicago (icing disengaged autopilot, surprise manual recovery failed)
In 1994, the ATR-72 encountered icing at 16,000 ft and was instructed to descend and maintain 10,000 and subsequently 8,000 ft. The crew could see the large amount of ice buildup on the wings (more on the right wing than the left). Unknown to the crew, the autopilot was countering a tendency to turn right. Eventually the autopilot reached the limit of its ability and (by design) automatically disengaged. This caused the aircraft to suddenly corkscrew into a sharp right turn, right roll, and 15-degree pitch down. The surprised crew was unable to regain control. Sixteen passengers perished in the crash (Degani, 2004).
2.4Lockheed L-1011 Crash Over the Florida Everglades (automation state change not communicated to pilot)
In this 1972 incident, the entire flight crew was engaged in troubleshooting a problem with a landing gear indicator light and did not recognize that the altitude hold function of the autopilot had been inadvertently switched off. Meanwhile the aircraft slowly descended into the Florida swamp.
Although several factors contributed to this accident, a major factor was poor feedback on the state of automation provided by the system. The disengagement of automation should have been clearly signaled to the human operator so that it could have been validated. Most current autopilots now provide an aural and/or visual alert when disconnected. The alert remains active for a few seconds or requires a second disconnect command by the pilot before it is silenced. Persistent warnings such as these, especially when they require additional input from the pilot, are intended to decrease the chance of an autopilot disconnect or failure going unnoticed. (National Transportation Safety Board [NTSB], 1973)
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