What happened
On June 10, 2016, a Cessna 310G, registration N8943Z, was involved in an accident at Orlando Apopka Airport (X04) in Apopka, Florida. The flight was a post-maintenance test flight following an annual inspection, and the aircraft had not been operated for two years prior to this flight.
After departing X04, the pilot performed two touch-and-go landings on runway 33. Following a go-around necessitated by another aircraft on the runway, the pilot attempted a full-stop landing. The pilot reported that the touchdown was normal and occurred in the typical location. After retracting the flaps and allowing the aircraft to slow aerodynamically, the pilot applied the brakes near the end of the runway.
At that time, the left brake failed to function. The aircraft began drifting to the right, and as the speed decreased, the deviation became more pronounced. The pilot attempted to pump the left brake and apply pressure, but the pedal went to the floor without effect. To prevent the aircraft from leaving the runway, the pilot secured the engines and applied the right brake to maintain control. The aircraft exited the right side of the runway and struck upsloping terrain, resulting in substantial damage to the left horizontal stabilizer. The pilot was not injured.
The investigation
An FAA operations inspector performed initial testing of the pilot-side brakes and found no discrepancies. However, testing of the co-pilot-side brakes revealed a discrepancy with the right brake. No leaks were found in the brake system, and fluid levels in both master cylinders were correct.
Subsequent examination of the brake master cylinders by an FAA airworthiness inspector revealed that while the right brake worked perfectly when removed, the left brake failed during testing. After the first actuation, the actuating rod in the left master cylinder leaked internally to the bottom. Disassembly of both cylinders showed that the o-rings were in reasonable condition with no visible cuts or tears. Both cylinders contained a dark, crusty compound and a small washer in the reservoir. Due to hydraulic fluid damage, the data plates on the master cylinders were illegible, making it impossible to identify part or serial numbers.