DEHAVILLAND DHC-6-100 near Hampton, GA — 2011-03-08

Probable cause

The pilot did not maintain airspeed while maneuvering, which resulted in an aerodynamic stall.

NTSB narrative

The airplane had not been flown for about 5 months and the purpose of the accident flight was a maintenance test flight after both engines had been replaced with higher horsepower models. Witnesses observed the airplane depart and complete two uneventful touch-and-go landings. The airplane was then observed to be struggling to gain altitude and airspeed while maneuvering in the traffic pattern. One witness, who was an aircraft mechanic, reported that he observed the airplane yawing to the left and heard noises associated with propeller pitch changes, which he believed were consistent with the "Beta" range. The airplane stalled and impacted trees in a wooded marsh area, about 1 mile from the airport. It came to rest about 80-degrees vertically. Examination of the wreckage did not reveal any preimpact malfunctions; however, the lack of flight recorders and the condition of the wreckage precluded the gathering of additional relevant information. Damage observed to both engines and both propellers revealed they were likely operating at symmetrical power settings and blade angles at the time of the impact, with any differences in scoring signatures likely the result of impact damage. The reason for the yawing and the noise associated with propeller pitch changes that were reported prior to the stall could not be determined.

Analysis

Primary failure mode

Loss of control

First missed decision gate

Pilot could have aborted the approach when engine noise fluctuated and altitude was not gained.

NTSB coding

• Loss of control in flight · Approach

Evidence available

• Photos
• 27 docket documents

Docket documents27

• NTSB Party Representative Form and Gudianceform
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Witness Statementsinterview
• Airplane Bill of Saleother
• Maintenance Records (excerpts)other
• Pilot Logbook (excerpts)other
• Refueling Recordsother
• Weather Observationsother
• Hartzell Propeller Teardown Report (includes 12 photographs)photos
• Photograph # 1 – Airplane as it came to rest (viewing right-underside)photos
• Photograph # 10 – Detailed view of right engine compressor turbine disc, blades, and shroud (Taken by Pratt & Whitney Canada).photos
• Photograph # 11 – Detailed view of scoring observed on right engine power turbine shroud (Taken by Pratt & Whitney Canada).photos
• Photograph # 12 – Left engine after recoveryphotos
• Photograph # 13 – Left engine data platephotos
• Photograph # 14 – Detailed view of left engine compressor turbine disc, blades, and shroud (Taken by Pratt & Whitney Canada).photos
• Photograph # 15 – Detailed view of scoring observed on left engine power turbine shroud (Taken by Pratt & Whitney Canada).photos
• Photograph # 16 – View of all six propeller blades after recovery and hub disassembly.photos
• Photograph # 2 – Airplane as it came to rest (viewing right-topside)photos
• Photograph # 3 – Airplane as it came to rest (viewing left side)photos
• Photograph # 4 – View of left wing suspended in treesphotos
• Photograph # 5 – View of left propeller assembly as found, partially buried in the groundphotos
• Photograph # 6 – Right propeller assembly as found, attached to right enginephotos
• Photograph # 7 – Left side and forward section of airplane after recoveryphotos
• Photograph # 8 – Right engine after recoveryphotos
• Photograph # 9 – Right engine data platephotos
• FAA Forensic Toxicology Accident Reportreport
• Pratt & Whitney Canada Engine Report (Exceprts)report

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