1. An unusual incident was observed during a 10 September 1976 British European Airways (BEA) flight (number 831) from Moscow to London. Between 1800 and 1900 hours, the aircraft was crusing at an altitude of approximately 33 thousand feet (9,900 meters), apparently inside the border of Lithuania, when a blinding, single source, constant intensity, and stationary light was observed off the starboard flight path of the air-craft. The light's distance was estimated to be approximately 10 to 15 miles (16 to 24 kilometers) off the aircraft's path and approximately five to six thousand feet (1,500 to 1,800 meters) below the aircraft, somewhat above a lower cloud layer. The light, which resembled a sodium vapor lamp (yellowish in color), and which was too intense to view directly for any period of time, completely lit the top of the lower cloud layer, giving it a glowing cast. 2. The light was of such interest that the BEA piot came onto the aircrafts intercom network, stated that he was somewhat concerned over its presence, and said he had asked Soviet authorities for identification of its source. The Soviet authorities came back with a negative identification response, suggesting that he should not ask questions. The light was observed for approcimately 10 to 15 minutes, until the aircraft had flown past and left the light source behind.