The second of two prototypes, this Piasecki YH-16A Transporter broke apart in mid-air on 5 January 1956, when the rear rotor shaft failed, allowing the blades to desynchronize and wobble into the plane of those of the forward rotor. Although the cause of the failure was determined not to be a design defect the program was scrapped.

The H-16 was the world's largest helicopter when first flown on 23 October 1953. The second and last example, seen here, was modified to turbine power and first flew as the YH-16A in June 1955, but crashed on 5 January 1956. The US Air Force and Army judged the type unsuitable for operational use. Photo from: Piasecki