What happened
On May 21, 2011, a Bell 204B helicopter, registration OB-1891-P, operated by Servicios Aéreos de Los Andes S.A.C., was performing a maintenance test flight at Cusco's Velasco Astete International Airport. The flight was intended to verify engine parameters following recent maintenance work.
Shortly after takeoff, while the pilot was increasing collective pitch, the aircraft experienced a sudden right-hand bank. The helicopter entered an uncontrolled lateral roll and translation at a very low altitude. Approximately 40 meters from the initial takeoff position, the aircraft struck the ground near the side of Runway 10. The impact was violent, causing the left skid to fracture and the transmission to detach. The pilot, a mechanic, and a quality inspector were on board; all three occupants sustained minor injuries and were treated by airport emergency services.
The investigation
The CIAA investigation focused on the aircraft's maintenance history and the mechanical state of the flight controls. Investigators discovered that a bellcrank (part number 204-001-352-1C2) had been removed from the aircraft to be used as a loan for another helicopter. Although maintenance logs indicated that the part had been reinstalled on April 16, 2011, physical evidence at the crash site proved that this work had not actually been performed.
Investigators also found that the maintenance personnel had falsified the aircraft's inspection records to show the discrepancy as resolved. The mechanic involved stated that the failure to reinstall the part was due to an excessive workload and the pressure of servicing multiple aircraft simultaneously. Furthermore, the investigation noted that the aircraft's Emergency Locator Transmitter (ELT) was not installed according to manufacturer recommendations, and the passenger manifest had omitted the weight of the third occupant.
Findings
- The primary cause of the accident was the loss of lateral cyclic control during takeoff due to the missing bellcrank in the flight control system.
- Maintenance personnel recorded the reinstallation of the missing component in the aircraft logs without physically performing the task.
- The process for managing part loans between aircraft did not follow the company's General Maintenance Manual procedures.
- High workload and inadequate oversight contributed to the failure to identify the missing component before flight.