N114MK

HISTORY OF FLIGHT On May 11, 2012, about 1435 Pacific daylight time, a Maule MX-7-235, N114MK, was substantially damaged when it veered off the runway and struck a ditch after landing at Roche Harbor airport (WA09), Roche Harbor, Washington. The pilot/owner was not injured. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no Federal Aviation Administration (FAA) flight plan was filed for the flight.

According to the pilot, he departed from Anacortes airport (74S) Anacortes, Washington, for the brief flight to WA09. Based on his observation of the wind sock, there was no wind, and he utilized 40 degrees of flap extension for the three-point landing on runway 7. Immediately after touchdown, the airplane veered "sharply left." The pilot applied full right rudder and some right brake, but he could not keep the airplane on the runway. The airplane departed the left (north) side of the runway, traversed a grassy area bounding the runway, and struck a drainage ditch located about 50 feet off the runway. The propeller, cowling, fuselage, and both main landing gear were damaged. The pilot stated that he believed that a mechanical malfunction of the braking system had occurred.

PERSONNEL INFORMATION

FAA information indicated that the pilot held a private pilot certificate with airplane single-engine land and instrument airplane ratings. The pilot reported a total flight experience of 1,600 hours, including 9 hours in the accident airplane make and model. He received his tailwheel endorsement in the accident airplane on May 6, 2012. His most recent flight review was completed in November 2011, and his most recent FAA third-class medical certificate was issued in June 2011.

AIRCRAFT INFORMATION

The airplane was manufactured in 1985, and was equipped with a Lycoming IO-540 series engine. The most recent annual inspection was completed on April 2012, when the airplane had a total time in service of about 1,373 hours. At the time of the accident, it had accumulated about 1,379 hours total time in service.

The airplane was involved in a previous landing accident in 2003, before it was acquired by the current owner. The National Transportation Safety Board determined that the previous accident was due to mechanical malfunctions of the normal and parking brake systems.

METEOROLOGICAL INFORMATION

The 1453 automated weather observation at an airport located 7 miles southeast of WA09 included winds from 360 degrees at 9 knots, clear skies, temperature 14 degrees C, dew point -1 degrees C, and an altimeter setting of 30.30 inches of mercury.

AIRPORT INFORMATION

The airport was equipped with a single paved runway, designated 07/25. The runway was asphalt, and measured 30 feet by 3,593 feet. Airport elevation was 100 feet above mean sea level.

FAA design and construction guidance for airports is contained in a series of FAA Advisory Circulars (ACs). Although airports such as WA09 that do not serve air carriers are not required to be in compliance with those ACs, the AC information is the only FAA-published airport design guidance.

AC 150/5300-13A, "Airport Design" defines a zone designated as the Runway Safety Area (RSA), which "enhances the safety of aircraft which undershoot, overrun, or veer off the runway." The AC specifies that the RSA must be clear "of objects, except for objects that need to be located in the RSA because of their function," and that the RSA must be "graded and have no potentially hazardous ruts, humps, depressions, or other surface variations." RSA dimensions are a function of the size aircraft that the airport serves. For the accident airplane, the AC specified an RSA width of 120 feet (60 feet each side of the centerline), meaning that if the airport was to be in compliance with the CA, the ditch would have to be located at least 60 feet from the runway centerline.

The drainage ditch roughly paralleled most of the WA09 runway, and meandered variously between 40 and 70 feet from the runway centerline.

ADDITIONAL INFORMATION

Brake System

The airplane was equipped with two independent wheel brakes that were actuated by two separate brake master cylinders, one each for the left and right brake. The only set of brake pedals and cylinders were at the pilot's position. Depression of the brake pedal actuated a piston rod in the master cylinder, which applied hydraulic pressure to the brake pad. Release of the pedal permitted the piston rod to be back-driven by a spring, which in turn released brake pressure at the wheel. There were no provisions for a pilot to directly move the piston rod to release brake pressure.

The parking brake system utilized a cable-actuated lever on each master cylinder to grip and hold each brake master cylinder piston rod in place, in order to retain applied brake pressure. According to Maule documentation, the brake master cylinders, including their piston rods, were designed and produced by at least three different vendors (Scott, Gerdes, and Cleveland) as a generic component for applications on multiple aircraft; they were not specifically designed for the airplane or the airplane manufacturer. The parking brake lever was designed and installed by the airplane manufacturer.

Except for the tactile and transitory feedback from the normal procedure where pilots apply brakes to stop wheel spin shortly after liftoff, there are no provisions for a pilot to detect whether brake pressure is applied when the airplane is airborne. Once airborne, the pilot has no way to detect, prevent, or eliminate a locked wheel.

Observed Installation and Damage

On June 20 2012, an aircraft mechanic conducted a detailed examination of portions of the brake control mechanism, and observed a mechanical condition that can result in inadvertent and irreversible brake application by locking the brake master cylinder piston rod in position. Information provided by the mechanic confirmed that the brake master cylinder installed on the airplane was the correct component specified by Maule.

The observed deficient condition was a result of the parking brake lever which, during normal operation, mechanically damaged the left brake master cylinder piston rod. The lever formed multiple circumferential gouges and ridges on portions of the piston rod. The nominal outside diameter (OD) of the rod was 0.308 inches, but the damaged areas exhibited an OD of 0.312 inches. The nominal inside diameter (ID) of the brake master cylinder bushing, through which the rod normally translated, was 0.311 inches. This resulted in an interference fit between the damaged rod and the bushing. If the brake pedal was depressed sufficiently to drive the damaged portion of the rod into the bushing, the rod would no longer be free to slide unrestricted through the bushing. The spring used to return the rod to the 'no brake pressure' position was of insufficient strength to overcome the resistance of the interference fit. Therefore the rod would not return to release brake pressure, and the wheel would be partially or fully locked.

The investigation was unable to determine whether all the parking brake lever hardware was installed, or was installed correctly, on the affected brake master cylinder, but the examining mechanic did not report any anomalies with the assembly, and the pilot did not report any problems with the functioning of the parking brake. The mechanical properties (material, hardness, etc.) of the piston rod and the lever were not determined, or compared to their design specifications.

The examining mechanic suggested that an increase in the clearance between the piston rod and its bushing in the brake master cylinder would help eliminate the problem. Due to agency resource limitations, the lack of certain technical information, and the potential for unintended consequences of such a design change, the investigation did not pursue the viability of this suggestion.

The pilot did not report any previous incidents of dragging or stuck brakes on this airplane. The investigation was unable to determine the total time in service of the damaged brake master cylinder piston rod. This condition has been observed on other Maule airplanes, and was the cause of a previous accident to the same airplane, with a different pilot and owner, in 2003.

Maule Service Information

In July 2011, Maule Aircraft issued Service Letter (SL) 71, entitled "Parking Brake Control." The SL was applicable to all Maule airplanes, was assigned a "mandatory" status by Maule, and was prompted by inadvertent and/or undetected brake application by the parking brake system. The SL was based on a similar end problem (uncommanded locking of the brake master cylinder piston rod in the 'brakes applied' position) but cited and corrected a different potential cause – improper rigging of the parking brake actuation cable. The accident airplane parking brake cable was found to be properly rigged, in compliance with the Service Letter.

The airplane maintenance manual did not contain any specific inspection citations or component life limits for the brake master cylinder piston rod, and no Maule Service Letters or Service Bulletins concerning the brake master cylinder piston rod have been issued.

Inspection Information

Paragraph (c) of 14CFR Part 43.15 stated "Annual and 100-hour inspections. (1) Each person performing an annual or 100-hour inspection shall use a checklist while performing the inspection. The checklist may be of the person's own design, one provided by the manufacturer of the equipment being inspected or one obtained from another source. This checklist must include the scope and detail of the items contained in appendix D to this part."

14CFR Part 43, Appendix D "Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual and 100-Hour Inspections" contained the following guidance to perso...