NTSB Factual Report

HISTORY OF FLIGHT

On June 11, 2013, about 0915 central daylight time, an experimental, amateur-built Rogers T-51 Mustang kit airplane, N548RR, impacted terrain during a forced landing following a loss of engine thrust near St Francis, Kansas. The pilot was uninjured. The airplane sustained substantial damage. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a test flight. Visual meteorological conditions prevailed for the flight, which did not operate on a flight plan. The local flight originated from the Cheyenne County Municipal Airport (SYF), near St Francis, Kansas, about 0900.

The pilot reported that he had been flying about 15 minutes, at a cruise altitude of 4,000 to 5,000 feet, when the propeller control had no effect on engine rpm. He said, "After several attempts to slow the rpm's, the prop cycled to full bite, lugging the engine." The propeller remained that way until the pilot performed a wheels up landing on a rough county road.

PERSONNEL INFORMATION

The 65-year-old pilot held a private pilot certificate with a single-engine land rating. He held a FAA third-class medical certificate that was issued on May 2, 2013, with a limitation to wear corrective lenses. He reported that he had accumulated 2,415 hours of total flight time and 50 hours of total time in the same make and model as the accident airplane. His last flight review was on August 1, 2011.

AIRCRAFT INFORMATION

The airplane, serial number M08SV6SOHK0142, was a low wing, tandem, two-seat, dual control kit airplane. FAA records indicated that its application for a U.S. airworthiness certificate 8130-6 form was endorsed on March 9, 2012.

The airplane was powered by a Honda 3.5L V6 engine with serial number J35A6-1206695, which drove a composite, constant speed, 4-bladed, 84 inch, Whirl Wind Hydraulic Propeller with serial number 100-4-84-171. A Jihostroj P-910-028/A governor with serial 102-008 controlled the propeller's pitch. The pilot reported that the airplane had accumulated 50 hours of total time at the time of the accident, and it had 20 gallons of aviation gasoline on board when it departed on the accident flight.

According to the kit manufacturer, the T-51D was rated at a +6g / -4g load limit capability at a weight of 1,650 lbs. When equipped with the Honda 3.5L V6 engine and the landing gear retracted, the T-51D cruised around 180 mph and had a climb rate of approximately 2,500 feet per minute. In landing configuration, the stall speed was in the 50 mph range. The airplane had a fuel capacity of 25 gallons.

The P-910-028/A propeller governor is a centrifugal hydraulic governor designed for control of single-acting hydraulic aircraft engine propellers. The governor regulates the set speed of the propeller by means of adjusting the blade angle depending on immediate flight conditions. The governor uses high oil pressure to increase the propeller blade angle. The force of spring, aerodynamic moments of propeller blades, and mass moments of propeller blades or weights act against this pressure.

METEOROLOGICAL INFORMATION

At 0935, the recorded weather at SYF was: Wind calm; visibility 10 statute miles; sky condition clear; temperature 27 degrees C; dew point 10 degrees C; altimeter 29.78 inches of mercury.

WRECKAGE AND IMPACT INFORMATION

A Federal Aviation Administration (FAA) inspector examined and documented the airplane at the accident site. A review of images revealed the airplane sustained substantial wing and fuselage damage consistent with a wheels up landing.

TESTS AND RESEARCH

The accident engine was removed from the airplane by the pilot and was shipped to the airplane kit manufacturer where it was test run under the supervision of a FAA inspector. The engine was operational and gauge readings, taken from a pressure gauge plumbed into the line from output of propeller governor to gearbox, were observed. With uncontrolled engine rpm, oil pressure was constant and propeller pressure cycled as designed in its specified pressure range. After testing was completed, the propeller gearbox was drained of the fresh oil. The oil presented a used appearance consistent with oil that had not been changed as recommended by the manufacturer.

The propeller governor was bench tested. The governor did not meet test specifications. The governor was subsequently torn down. Separation of the actuator valve face from the body revealed the presence of foreign debris intrusion. Its spool valve movement was restricted and not self-retracting. The flyweights were unable to function as required due to the stiffness and resistance created by the spool valve. Witness marks consistent with wear were observed on the spool valve spring, spool valve spring face, and on the actuator valve face. The spool valve and flyweights did not move freely and were extracted with the use of pliers. The governor was cleaned and re-assembled. It was operational during a subsequent bench test.

The propeller hub was tested with the application of shop air and no anomalies were observed during its test.

The accident propeller governor was subsequently shipped to its manufacturer in the Czech Republic by the kit manufacturer. An investigator from the Air Accidents Investigation Institute oversaw the testing and examination of the accident propeller governor. The governor was operational during their testing, however a post-test disassembly revealed wear consistent with abrasion debris or impurities.

ADDITIONAL DATA/INFORMATION

The Jihostroj Operation and Installation Manual for Constant Speed Propeller Governors, in part, stated:

Dirty Engine Oil

Contaminants in dirty engine oil can cause blockage of close tolerance passages in governor, leading to erratic operation.

Solution: Flush the governor in order to cleaning out contaminated oil.

Pollution of Engine Oil

Excessive dirt in the engine oil pollution can cause governor seizure.

Solution: Overhaul the governor.

The kit manufacturer returned the accident engine to the pilot along with a replacement governor. The pilot reported that the accident airplane was repaired, the engine and new governor were re-installed, and the airplane is operating without any anomalies.

NTSB Probable Cause

Foreign debris in the propeller governor, which led to excessive wear in the governor and its subsequent in-flight failure.