On January 18, 1969, at approximately 18:21 PST, the Boeing 727 operating the flight crashed into Santa Monica Bay, Pacific Ocean, about 11.5 miles (18.5 km) west of Los Angeles International Airport, four minutes after takeoff, killing all 38 on board.
The crew of Flight 266 was Captain Leonard Leverson, 49, a veteran pilot who had been with United Airlines for 22 years and had almost 13,700 flying hours to his credit.
The crew radioed to departure control that they only had one functioning generator and needed to come back to the airport, but it turned out to be their last communication, with subsequent attempts to contact Flight 266 proving unsuccessful.
Consequently, the crew lost control of the aircraft and crashed into the ocean in a steep nose-down angle, killing everyone on board.
Three and a half hours after the crash three bodies had been found in the ocean along with parts of fuselage and a United States mail bag carrying letters with that day's postmark.
The wreckage was in approximately 930 feet (280 m) of water and had been severely fragmented, however the relatively small area in which it was spread indicated an extremely steep, nose-down angle at impact.
NTSB investigators could not explain the sparking seen by witnesses on the ground and theorized that it might have been caused by debris being sucked into the engine, a transient compressor stall or an electrical system problem that led to the eventual power failure.
Busy operating schedules and limited aircraft availability meant that repair work on N7434U was put on hold, with nothing that could be done in the meantime except to disable the #3 generator.
It was theorized that the non-activation of the backup electrical system might have been for one of several reasons: The CVR and FDR both lost power just after the crew informed ATC of the fire warning on engine #1.
The accident prompted the Federal Aviation Administration to require all transport-category aircraft to carry backup instrumentation, powered by a source independent of the generators.