Amateur-built TCOW SMITH CUB N810GL accident near Cascade, Idaho

Probable cause

A gouge in the right brake master cylinder piston O-ring, which resulted in a loss of brake pressure and reduced effectiveness after landing. Contributing to the accident was the pilot’s decision to operate the airplane with an ongoing brake issue.

NTSB analysis

The private pilot/owner of the ultralight airplane was conducting a personal flight. He stated that, after landing, he applied the brakes to slow the airplane. He did not feel any right brake resistance, and the airplane swerved left due to left brake application. He attempted to correct with rudder inputs, but the airplane ground looped to the left, which resulted in the right landing gear collapsing and damage to the right wing. The pilot stated that the he had recently been having ongoing difficulty with the airplane's right brake function.

Examination and disassembly of the right brake master cylinder revealed that the master cylinder piston O-ring had a gouge in it. The gouge likely allowed brake fluid to bypass the seal, which resulted in a loss of brake pressure and, therefore, reduced effectiveness after landing.

Text from the NTSB. Open the NTSB docket for WPR15LA218 for the full record.