However, Republic of Vietnam Air Force pilots had severe difficulties operating the B-57. Vietnamese crews suddenly began to complain of various illnesses, which grounded many trainees and brought their training to a standstill. In addition, on 8 January 1966 a B-57 was destroyed in a training accident, further lowering morale. Some Vietnamese crews flatly stated that they could not physically perform the maneuvers required in the B-57. To make matters even worse, Major Nguyen Ngoc Bien, the leader of the VNAF B-57 program, was killed in a freak ground accident on 23 February 1966 at Da Nang. The death of Major Bien, who was well-liked and well-respected by both Vietnamese and Americans, resulted in a complete loss of any incentive for the Vietnamese crewmen to stay with the B-57, and from this point on there was very little Vietnamese activity in the B-57 program. On 20 April 1967, the VNAF B-57 operation was formally terminated.