What happened
On February 15, 2000, a Bell 407 helicopter, registration PT-YZJ, operated by the Brazilian Federal Highway Police (Departamento de Polícia Rodoviária Federal), was conducting training maneuvers in Brasília, DF. Following a rappelling training session, the instructor pilot performed an autorotation maneuver from a hover, transitioning into a running landing.
During the flare phase of the landing, a crew member in the passenger cabin reported hearing a noise. Upon completing the landing on the sloped terrain, the crew discovered that the left vertical finlet of the horizontal stabilizer had been severed. There were no injuries reported during the incident.
The investigation
CENIPA investigators examined the aircraft and the circumstances of the landing. The investigation focused on whether the pilot applied excessive cyclic input to arrest the aircraft's movement on the sloping ground. While the aircraft's flight manual instructs pilots to disregard the cyclic limit warning light during running landings on uneven terrain, the investigation looked into the mechanical interaction between the rotor blades and the tail structure.
The investigation also reviewed the suitability of the training site. The area used for the autorotation training was not a certified landing site and lacked the necessary infrastructure for emergency response. Maintenance records were reviewed, and no mechanical failures or deviations from operational limits were found in the main rotor, transmission, or skids. The investigation noted that similar incidents involving the Bell 407 have been recorded globally, though the manufacturer had not issued specific alerts regarding this issue at the time.
Findings
- Improper training location: The instructor pilot selected an uncertified, sloped area for performing high-risk autorotation maneuvers.
- Inadequate supervision: The operational training department permitted maneuvers to be conducted in a location unsuitable for such instruction.
- Excessive control input: It is highly probable that the pilot applied excessive cyclic aft input to stop the aircraft's forward motion on the slope, causing the main rotor blades to flex downward and strike the left vertical finlet.
- Design factors: The aircraft's design, which includes a leftward mast tilt and aerodynamic lift variations between the advancing and retreating blades, contributed to the rotor disk dipping toward the left stabilizer during the maneuver.