NTSB Factual Report

On November 12, 2016, about 1215 Alaska standard time, a tailwheel-equipped Cessna A185F airplane, N4918Q, sustained substantial damage during the landing roll at the Ninilchik Airport, Ninilchik, Alaska. The certificated airline transport pilot and the pilot-rated passenger sustained no injuries. The airplane was registered to, and operated by, the pilot as a visual flight rules (VFR) flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91. Visual meteorological conditions prevailed at the time of the accident, and a VFR flight plan had been filed. The flight originated from the Soldotna Airport, Soldotna, Alaska, about 1200.

During a telephone interview with the National Transportation Safety Board (NTSB) investigator-in-charge on November 13, the flying pilot, who was seated in the right seat at the time of the accident, stated that after an uneventful touchdown on the slightly wet and gravel surface of runway 10, the right-side brake system did not function as designed, which resulted in an asymmetrical braking condition. As the airplane continued the landing roll, the airplane ground looped to the left and the right wing and right horizontal stabilizer impacted the runway surface. The airplane came to rest on the runway without further incident.

The accident pilot stated that the previous landing was accomplished by the pilot-rated passenger and she reported no issues with the brake system during that landing sequence. The pilot further stated at the time of the accident, the wind condition originated from the north, about 10 to 15 knots. The airplane sustained substantial damage to the right wing and the right horizontal stabilizer.

In a written statement from a Federal Aviation Administration (FAA) aviation safety inspector (ASI) on November 16, he reported that he conducted an onsite examination of the airplane's brake system. He reported that he attempted to actuate the right brake, but the brake just went to the full travel stop. The right brake master cylinder filler plug was removed and a small tie wrap was utilized as a dip stick, and no fluid was observed on the tie wrap. The bottom of the fuselage and the right brake caliper were visually examined, and no signs of fluid leaks were observed. The accident pilot was asked if he previously observed the ground under the brake calipers at his parking space for evidence of any fluid leaks and the pilot reported he did look and did not observe any signs of fluid. The ASI additionally reported that the runway utilized by the accident pilot was in a useable condition, and that ice patches on the side of the runway were not a factor with the accident sequence.

In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot stated that the accident may have been avoided if he depressed the brakes prior to landing to confirm both were functioning.

METEOROLOGICAL INFORMATION

The closest weather reporting facility was the Homer Airport, Homer, Alaska. At 1153, an Aviation Routine Weather Report (METAR) was reporting in part: wind from 080 degrees at 17 knots, gusting 24 knots; visibility 6 statute miles; sky condition broken 3,600 feet; temperature 45 degrees F; dew point 37 degrees F; altimeter 29.11 inHg.

TESTS AND RESEARCH

In a written statement from the accident pilot on December 20, he reported that the entire brake system was tested. The testing revealed that the right brake had an "extremely small leak (one drop)" from both o-rings at 500 pounds per square inch. The rest of the brake system appeared normal and no signs of brake fluid were found on the underside of the fuselage. He reported he assumed the leak was small and that only under pressure would it show signs of leaking, that is why no evidence of leaking was observed on any preflight activity prior to the accident. He further reported the o-rings on both calipers were replaced, the brake system was pressurized, and no further leaks were found.

In a written statement from the pilot on April 4, he reported that after replacing the brake lines, the right brake did not readily take fluid when pumped from the caliper. The right brake master cylinder was disassembled, and the spring was observed to be deformed. He reported that in certain positions, the spring would block the flow of fluid in or out.

ADDITIONAL INFORMATION

The FAA has published the Aviation Maintenance Technician Handbook – Airframe FAA-H-8083-31 (2012). This document discusses airplane brake systems and states in part:

Brake seals are very important. Without properly functioning seals, brake operation will be compromised or the brakes will fail. Over time, heat and pressure mold a seal into the seal groove and harden the material. Eventually, resilience is reduced and the seal leaks. New seals should be used to replace all seals in the brake assembly. Acquire seals by part number in a sealed package from a reputable supplier to avoid bogus seals and ensure the correct seals for the brake assembly in question. Check to ensure the new seals have not exceeded their shelf life, which is typically three years from the cure date.

NTSB Probable Cause

A loss of brake system fluid due to leaks in the o-rings, which resulted in asymmetrical braking and a subsequent loss of directional control during the landing roll.