United Airlines Flight 266
|Date||January 18, 1969|
|Summary||Mechanical failure leading to loss of electrical power|
|Site||Santa Monica Bay, California, USA|
|Aircraft type||Boeing 727-22C|
United Airlines Flight 266 was a scheduled flight from Los Angeles International Airport, Los Angeles, California to General Mitchell International Airport, Milwaukee, Wisconsin via Stapleton International Airport, Denver, Colorado with 38 on board. On January 18, 1969 at approximately 18:21 PST it crashed into Santa Monica Bay, Pacific Ocean about 11.5 miles west of Los Angeles International Airport four minutes after takeoff.
Rescuers (at the time) speculated that an explosion occurred aboard the plane, a Boeing 727. 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. Hope was dim for survivors because United's domestic flights do not carry liferafts or lifejackets. A Coast Guard spokesman said it looked "very doubtful that there could be anybody alive."
Up until 2013, United used "Flight 266" designation on its San Francisco-Chicago(O'Hare) route.
The 727 used on the flight had had a nonfunctional No. 3 generator for the past several days. Per standard procedure, the crew placed masking tape over the switches and warning lights for the generator. Approximately two minutes after takeoff, they reported a fire warning on Engine No. 1 and shut it off. 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 and subsequent attempts to contact Flight 266 were unsuccessful. Shortly after the Engine No. 1 shutdown, the No. 2 generator also ceased operating for unknown reasons. All of the available evidence produced during the course of the investigation, did not enable the NTSB to determine why the number two generator also failed, after it became the sole source of power for the plane, nor why the "standby electrical system either was not activated or failed to function."
Several witnesses saw Flight 266 take off and reported seeing sparks emanating from either Engine No. 1 or the rear of the fuselage while others claimed an engine was on fire. Salvage operations were conducted to recover the wreckage of the aircraft, along with what remains of the passengers and crew could be located, but not much useful information was gleaned as the cockpit instruments were not recovered. The wreckage was in approximately 930 feet (280 meters) 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. The No. 2 and 3 engines suffered severe rotational damage from high RPM speeds at impact, but the No. 1 engine had almost no damage due to having been powered off. No evidence of any fire or heat damage was found on the engines, thus disproving any of the witnesses' above-mentioned claims. The small portion of the electrical system that was recovered did not provide any relevant information. NTSB investigators could not provide any explanation for 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 perhaps an electrical system problem that led to the eventual power failure. They also were unable to explain the Engine No. 1 fire warning in the absence of a fire, however it may also have been due to electrical system problems or a cracked duct that allowed hot engine air to set off the temperature sensors. Assorted tests indicated that it was quite possible for the No. 2 generator to fail from an overload condition due to the operating load being suddenly shifted onto it following the No. 1 generator's shutdown, and this was maintained as a possible cause of the failure.
In regard to the nonfunctional No. 3 generator, Plane N7434U was recently been fitted with a generator control panel that had been passed around several different UAL aircraft due to causing assorted malfunctions. After being installed in N7434U the month prior to the ill-fated flight, it once again caused operating problems and the No. 3 generator was swapped with a different unit. Since that generator was subsequently tested and found to have no mechanical issues, the control panel was therefore held to be the culprit after it caused further malfunctions with the replacement generator. Busy operating schedules and a limited number of available aircraft meant that repair work on N7434U was put on hold and nothing could be done in the meantime except disable the No. 3 generator. The NTSB investigators believed that the inoperative No. 3 generator probably was not responsible for the No. 2 generator's in-flight failure since it was assumed to be isolated from the rest of the electrical system.
With the loss of all power to the lights and flight altitude instruments, while flying at night in instrument conditions, the pilots quickly became spatially disorientated and utterly helpless to know what inputs to the flight controls were necessary to keep the plane flying in the normal, upright attitude. Consequently they lost complete control of the aircraft and it crashed into the ocean in a steep nose-down angle, killing everyone on board. The flight control system would not have been affected by the loss of electrical power since it relied on hydraulic and mechanical lines, thus it was concluded that loss of control was due to the crew's inability to see around the cockpit. It was theorized that the backup electrical system had not been activated because the crew could not locate the switch for it in darkness.
At the time, a battery powered back-up source for critical flight instruments was not required on commercial aircraft. The accident prompted the Federal Aviation Administration to require all transport category aircraft to have new backup instrumentation installed, and powered by a source independent of the generators.
- The Board determines that the probable cause of this accident was loss of attitude orientation during a night, instrument departure in which the attitude instruments were disabled by loss of electrical power. The Board has been unable to determine (a) why all generator power was lost or (b) why the standby electrical power system either was not activated failed to function.
On January 13, 1969, just five days before the crash of United Flight 266, a Scandinavian Airlines DC-8 on final approach to Los Angeles International also crashed into Santa Monica Bay. The jet broke in half on impact, killing 15. Thirty people survived in a portion of the fuselage that remained afloat.