What happened
During a scheduled mission from Dong Ha to Da Nang, an aircraft operated by the 138th Aviation Company went missing. The flight was conducted under visual flight rules (VFR), but the pilot encountered deteriorating weather conditions during the transit. At approximately 14:30 hours, the pilot established contact with Da Nang airfield radar control, reporting a heading of 125 degrees at an altitude of 3,000 feet and indicating that he was currently flying on instruments.
In an attempt to establish a clear radar picture, controllers instructed the pilot to activate his transponder; however, this action failed to resolve the visibility issues on the radar screen. After receiving a position report placing the aircraft 45 nautical miles from Dong Ha, Da Nang controllers directed the pilot to re-establish contact with Dong Ha, under the assumption that the aircraft was still within that station's coverage area. Following this instruction, radio communication was lost and never recovered.
The aircraft, carrying two fatalities (the pilot and one passenger), was last tracked in the region of South Vietnam situated roughly halfway between Da Nang and Hue. Due to active hostilities in the area at the time, a comprehensive search operation could not be conducted, and no trace of the crew or the airframe was ever found.
Findings
An investigation into the disappearance determined that if the pilot had maintained his reported course, the aircraft would have struck a mountainside in the vicinity of Hue.