What happened
On January 25, 2013, a Cessna 208, registration PT-OGL, was performing a local parachute launching flight at the Centro Nacional de Paraquedismo in Boituva, Brazil. During the short final approach to runway 06, the pilot reduced engine power for landing. The pilot reported that the propeller unexpectedly entered reverse pitch without being commanded, leading to a loss of control. The aircraft struck a ravine located just before the runway threshold, impacting the ground 78 meters ahead of the threshold. The impact caused substantial damage to the aircraft, including damage to the landing gear, flaps, and windshield, while the pilot sustained minor injuries.
The investigation
CENIPA investigators examined the engine and propeller components to verify the pilot's report of an uncommanded reverse pitch. The Pratt & Whitney PT6A-114 engine was subjected to borescope inspections and bench testing. While investigators found that the clearance at the carbon block working on the Beta ring (0.032 inches) exceeded the manufacturer's maximum limit of 0.010 inches, they determined this wear would cause the propeller to move toward a feathering pitch rather than reverse pitch. Furthermore, testing of the propeller governor showed normal operation without any ability to enter reverse mode.
Analysis of the propeller blades revealed characteristics of an impact occurring without power. Investigators also noted that the aircraft's approach speed was approximately 61 knots with full flaps, which was close to the stall speed, and that the pilot had performed nine landings earlier that day. The investigation concluded that the aircraft was not authorized by ANAC for parachute launching operations and noted that several maintenance logbook records were outdated.
Findings
- The pilot likely reduced engine power to idle before reaching the runway threshold while at a speed near the stall limit.
- This reduction in power resulted in a loss of lift, causing the aircraft to descend into the ravine.
- The pilot's judgment may have been compromised by the high number of landings performed during the same day.
- The propeller did not actually enter reverse pitch; the impact occurred with the engine not producing power.
- The aircraft was operating in a capacity (parachute launching) not authorized by the national aviation authority.