COPY
Mr. George S. Moore
Director
Flight Standards Service
Federal Aviation Agency
Washington, D. C. 20553
Dear Mr. Moore:
The United Air Lines Boeing 727 aircraft accident at Salt Lake City, Utah, on November 11, 1965, disclosed the possibility of mal-operation of the emergency lighting system which failed to illuminate the emergency exits for passenger escape to safety. To date there has been no substantiation of any lighting in the cabin area after the aircraft came to rest.
The system is designed to be operated by a three-position switch in the cockpit overhead electrical panel. An amber indicator light adjacent to the switch monitors switch position and availability of 28 V DC power from battery bus.
| OFF | — | lights "OFF," batteries not charging, indicator light "ON." |
| ARMED | — | lights "OFF," batteries charging if AC and essential DC power available, indicator light OFF. If AC and battery bus DC power fails, lights "ON." Indicator light remains "OFF." |
| ON | — | lights "ON," batteries-discharging, indicator light "ON." |
However, if the switch is left in the "ARM" position and the DC battery bus is still a complete circuit, the lights will-remain "OFF." This is the situation that undoubtedly took place.
To eliminate this physical operation during a period of emergency, it is recommended that a procedure be used so that the emergency lights are turned "ON" during all takeoff and landing operations of Boeing 707, 720, and 727 aircraft, as well as all other turbine powered aircraft with automatic emergency lighting systems. Also, the aircraft should be rewired so that a loss of electrical power source for normal cabin lighting activates
