Accident Overview
On September 17, 2009, about 0940 Alaska daylight time, a Grumman G-44A airplane, registration N86627, sustained substantial damage during a loss of control after landing at Merrill Field Airport, Anchorage, Alaska. The airplane was being operated as a visual flight rules postmaintenance check flight under 14 CFR Part 91. The commercial pilot and a maintenance technician were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Merrill Field about 0915.
Pilot's Account
The pilot stated that the purpose was a postmaintenance check flight after repairs to the right brake assembly. On approach, he lowered the landing gear and depressed both brake pedals to test hydraulic back-pressure. After an uneventful touchdown on Runway 07, a dry paved runway, he applied brakes. While depressing both pedals, the right brake pedal unexpectedly went to the floor, and the airplane swerved left. He released pedal pressure, applied full right rudder, but could not correct the swerve, resulting in a ground loop to the left, striking the right wing on the runway. The right wing and aileron sustained substantial damage. Postaccident examination revealed a broken hydraulic supply line fitting on the right brake assembly, with hydraulic fluid sprayed in the wheel-well.
Maintenance Technician's Account
The technician who performed the repairs stated that the hydraulic supply line fitting was not removed during his work. After the accident, he inspected the broken fitting and suspected it might be an unapproved or "bogus" part due to an atypical thread pattern, despite having an "AN" stamp.
Pilot/Owner Statement
The pilot/owner noted that the brake line fittings had not been changed during his ownership. Review of maintenance logbooks did not show any previous work on the hydraulic fittings.
NTSB Materials Laboratory Examination
The broken fitting was sent to the NTSB Materials Laboratory. Examination on November 18, 2009, revealed two distinct fracture surface textures: one dull and grainy (overload), and one shiny and smooth with multiple ratchet marks and crack arrest marks consistent with fatigue.
Fitting Identification
The fitting was marked "AN", indicating approval for aircraft use. However, a nearly identical industrial fitting (JIC) is available. The two are visually indistinguishable except for the "AN" mark. The key difference is in thread design: JIC uses a class 2 thread with a flat or partially rounded root, while AN uses a class 3 thread with controlled root radius for higher fatigue strength. Measurement of the fractured fitting's thread pitch diameter was consistent with a class 2 (JIC) fitting, not intended for aircraft use.
FAA Advisory
On July 22, 2008, the FAA issued Advisory Circular 21-29C, change 1, providing guidance for detecting and reporting suspected unapproved parts.
Aftermath
The airplane owner/pilot replaced all "AN" hydraulic fittings to ensure no remaining unapproved parts.