What happened
On 18 May 1969, at approximately 12:05, a US Marine Corps KC-130F tanker departed Da Nang Air Base to perform a scheduled in-flight refueling mission near the Hue Phu Bai area. During the operation, the tanker was flying southbound along the South Vietnam coastline while providing fuel to two McDonnell F-4B Phantom fighter aircraft, identified by registrations 152270 and 151450. The aircraft were performing a descending maneuver known as tobogganing.
Simultaneously, another F-4B Phantom (registration 151001) was traveling westbound toward the Hue Phu Bai military zone. This third fighter approached the tanker and its refueling formation at a high closing speed of roughly 700 knots. The collision occurred when the F-4B struck the number four engine and the starboard refueling pod of the KC-130F. While the radome of the colliding fighter cleared the propeller, the cockpit impacted the engine. This impact caused the F-4B to crash into the sea, resulting in 2 fatalities for the crew of that aircraft.
The collision also affected the other aircraft in the formation. One refueling F-4B (151450) was struck by debris and sprayed with fuel after plugging into the starboard drogue, leading to a loss of engine power and an uncontrolled inverted flight before crashing at sea; however, both crew members successfully ejected and were rescued. The second refueling aircraft (152270) sustained minor structural damage but was able to return to Chu Lai Air Base safely. Following the impact, the KC-130F also crashed into the ocean.
Findings
An investigation into the event determined that the primary cause of the collision was a near head-on convergence between the westbound F-4B and the southbound tanker formation at extremely high closing speeds.