What happened
While cruising at FL350, the number 2 generator constant speed drive (CSD) failed. During the subsequent handling of the failure, the crew inadvertently disconnected the number 1 generator CSD. The crew attempted to start the APU, but these attempts were performed above the proper start envelope and were aborted following a hot start.
The aircraft descended using emergency electrical power. The crew elected to land at an airport that was inadequate for the aircraft type. For the approach, the crew chose a no-flap configuration and decided to extend the landing gear using the emergency method, even though both systems were functional via normal means. This decision was driven by the fact that landing gear and flap position indicators are unavailable when the aircraft is operating on battery power.
The aircraft touched down at a high speed and departed the end of the runway, causing damage to the number 1 engine and the landing gear. Following the stop, the crew failed to manually depressurize the cabin. The evacuation was delayed until a knowledgeable passenger entered the cockpit and performed the manual depressurization.
Findings
The investigation found that while the operator's aircraft operating manual included procedures for starting the APU, it did not include an APU start envelope chart.