Amateur-built Titan T-51 N51FB accident near Goodyear, Arizona

Probable cause

Failure of the propeller speed reduction gearbox input drive gear during the airplane’s initial climb for reasons that could not be determined due to extensive damage.

NTSB analysis

The airline transport pilot indicated that, immediately after takeoff for the local flight, the experimental, amateur-built airplane began to vibrate. As he transitioned the airplane to the downwind leg, the vibration increased, and the engine then experienced an overspeed and lost all power. The cockpit filled with smoke and the pilot subsequently performed a forced off-airport landing, which resulted in substantial damage to the left wing and aft fuselage.

The airplane had accrued about 43 flight hours since its construction, which was completed about 2 years before the accident.

Examination of the propeller speed reduction gearbox revealed that the teeth of the input drive gear had separated, which caused a loss of drive continuity to the propeller. The drive and idler gears did not appear to meet the manufacturer's case hardness requirements; however, evidence suggests that the gearbox had undergone severe heat buildup during the failure sequence, which may have subsequently altered the hardness. Oil starvation or exhaustion likely did not occur, as the gearbox bearings were intact and largely undamaged. Due to damage sustained to the gears, an accurate assessment of the initial failure mode could not be determined. Thus, the investigation could not determine the reason for the failure of the propeller speed reduction gearbox input drive gear.

Text from the NTSB. Open the NTSB docket for WPR17LA121 for the full record.