On April 21, 1968, Captain Floyd W. Olsen, aircraft commander; WO1 Robert C. Link, pilot; Sp5 Frankie B. Johnson, Jr., crew chief; Sp4 Larry C. Jamerson, doorgunner; SFC Lyle E. Mackedanz and Sp4 James E. Creamer, passengers; were aboard a UH1H helicopter (serial #66 16209) which was flying a combat mission with other aircraft in South Vietnam.

The aircraft remained with the assault aircraft during most of the operation until it was required to depart from Phu Bai, South Vietnam with rigging equipment for a recovery from LZ Zeghel. During the flight, Cpt. Olsen acknowledged a radio transmission which stated the aircraft's secondary mission, the recovery operation at LZ Zeghel, had been cancelled because of the tactical situation and inclement weather conditions. Following the acknowledgement of the cancelled mission, the aircraft was lost. Although there were several unsuccessful attempts to contact him, the ram checks of all airfields and camps in the area were conducted, no further contact was made with Cpt. Olsen.

On April 22, an extensive, though unsuccessful air search was conducted from dawn until 1830 hours. On May 8, elements of the 8th ARVN Airborne Division found the ID tags of Sp5 Johnson in a 3/4-ton truck, non-U.S. On May 25, a UH1C gunship of the 101st Airborne Division sighted a tail boom of a crashed helicopter. On May 26, the downed aircraft was positively identified by its tail number by a gunship of the 17th Armored Cavalry Helicopter Company.

On May 27, an on-ground inspection was conducted by 1st Battalion, 327th Airborne Infantry. They found the main rotor blades of the missing helicopter in a river bed 200 meters west of the tail boom. The area became insecure, and a search team came under enemy fire, curtailing search efforts prior to finding the main cabin section of the UH1H. Further investigation revealed that the helicopter was downed due to anti-aircraft artillery fire. Although the cabin section was not located, and no remains were found, the families of the men were informed that all aboard had been killed. No explanation was given as to why Johnson's dog tags had been found in a non-U.S. truck.

In the fall of 1985, a CIA document was declassified which contained drawings of a Viet Cong detention center which held U.S. servicemen in 1969 prior to their being sent north to Hanoi. In the document were greatly detailed drawings, lists of personnel, and lists of U.S. servicemen identified from photographs. Lyle Mackedanz' name was on a list of positively identified prisoners. Along with Mackedanz were the names of several POWs who were released in 1973. One of them has verified the authenticity of the report as far as the camp itself is concerned.