DEN07FA079 · Robinson R44 II

The local instructional flight was scheduled for a east departure from the airport and a flight south along the coastline. Several witnesses observed the helicopter approximately 200-500 feet above ground level (agl) in cruise flight along the coastline on a south heading. One witness, a former pilot and mechanic, reported he observed the helicopter in straight and level flight, then heard a change in "rotor noise, followed by a bang/pop/twang sound." The helicopter then "snap-rolled" to the left and descended into the terrain in a nose low attitude. Examination of the helicopter's flight control system revealed that the right forward servo to swashplate push-pull tube joint was disconnected and the attach hardware (bolt, lock nut, two washers, pal nut) was missing. The left forward servo to swashplate push-pull joint was connected; however, the nut was found partially engaged on the bolt threads, and the torque was "finger tight"; no pal nut was noted. Material analysis of the components revealed that only one of the two nuts for the left and right connections were installed, and then only finger tight. The nut on right servo connection rotated off during flight which allowed the bolt to extract itself and disconnect the servo from the push-pull tube. Prior to the accident flight, an inspection, which required the push-pull tubes to servo connections to be disassembled, was performed on the helicopter, and a 0.5-hour maintenance test flight. The mechanic who preformed the inspection, stated he forgot to properly secure the hardware for the left and right servo connections. The mechanic stated the reasons for the error were the following: 1. He was pulled," in all directions" by company personnel since his arrival at that facility; 2. The "reassembly was not opposite of the disassembly," which was a personal maintenance practice he used to eliminate errors; 3. Two nights prior to the completion of the inspection and the maintenance test flight, the apprentice providing assistance, wanted to stay late to finish with the mechanic a certain section of the inspection. As a result, the mechanic forgot to go back and secure the hardware connecting the two push-pull tube to servo joints; 4. The company was understaffed with maintenance personnel. According to the company's maintenance quality control program, any maintenance completed on a helicopter was to be inspected by another mechanic. A review of the program revealed that the mechanics were not following the program, and the company was not providing oversight and enforcing the program.

Verbatim NTSB analysis and probable cause from the NTSB dataset