Grumman AA5 N74420 accident near Brazoria, Texas

Probable cause

The propeller blade separation due to a fatigue fracture.

NTSB analysis

The student pilot and his flight instructor were conducting a local instructional flight when the airplane began to shake violently. A reduction of engine power revealed that the one of the propeller blades had separated about midspan. The flight instructor took control of the airplane and completed an uneventful forced landing in a nearby field. A postaccident examination revealed several fractured engine mounts.

A laboratory examination of the propeller revealed that about one-half of one blade had fractured. Further examination of the flat portion of the fracture surface revealed a pattern of crack arrest lines and striations that were consistent with fatigue cracking. The pattern of crack arrest lines indicated that the fatigue cracking emanated from the trailing edge tip of the blade. Damage to the fracture surface at the trailing edge tip of the blade obscured the exact initiation point of the fatigue cracking. The propeller had accumulated about 4,499 hours since its last overhaul, and about 11 hours since it was last examined during an annual inspection.

Text from the NTSB. Open the NTSB docket for CEN18LA292 for the full record.