ERA17LA105

The private pilot of the experimental, imported military airplane, stated that, after takeoff and while retracting the landing gear, he noticed that the pneumatic pressure was low. He then attempted to extend the landing gear using normal and emergency procedures, but the right main landing gear (MLG) remained retracted. The pilot subsequently conducted an emergency landing with the right MLG retracted. During the landing roll, he was able to keep the right wing from contacting the runway for about 1,000 ft. Once the wing contacted the runway, the pilot was unable to maintain directional control, and the airplane exited the right side of the runway. The right aileron sustained substantial damage. Examination of the airplane revealed that the pneumatic cylinder actuator that released the right MLG uplock was not functioning properly. Subsequent teardown examination of the right MLG uplock actuator revealed that moisture had entered the actuator over a period of time and corroded the internal components. The corrosion led to the failure of the actuator.

On February 1, 2017, about 1715 central standard time, an experimental S C Aerostar S A Yak-52, N624PT, was substantially damaged while landing at St. Elmo Airport (2R5), St. Elmo, Alabama. The private pilot was not injured. The airplane was operated by the private pilot as a personal flight conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the local flight that originated from 2R5 about 1700.The pilot reported that the landing gear was a pneumatic system. Shortly after takeoff and retracting the landing gear, he noticed that the pneumatic pressure was low. He then attempted to extend the landing gear using normal and emergency procedures, but the right main landing gear remained retracted. The pilot subsequently performed an emergency landing with the right main landing gear retracted. During the landing roll, he was able to keep the right wing from contacting the runway for about 1,000 feet. Once it contacted the runway, the pilot was unable to maintain directional control and the airplane came to rest upright in a grass area off the right side of the runway. The airplane was manufactured in the former Soviet Union in 1985, imported to the U.S. in 2003 and issued an FAA experimental airworthiness certificate. Some of the maintenance records did not import and the total time on the airframe could not be determined. The airplane's most recent annual condition inspection was completed on October 1, 2016. At that time, the engine had accumulated about 504 hours since overhaul. The airplane had been operated for 18 hours from the time of that inspection, until the accident. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed substantial damage to the right aileron. The inspector and a local mechanic also noted that the pneumatic cylinder actuator (P/N 524705-30) that released the right main landing gear uplock was not functioning properly. The mechanic subsequently performed a teardown examination of the actuator, which revealed that moisture had entered the actuator and corroded the internal components. The mechanic further stated that he planned to install a dryer system on the compressor of the airplane to prevent moisture from accumulating in the pneumatic lines. He also planned to subsequently disassemble and inspect the landing gear actuators every 2 or 3 years for corrosion. An organization of the make and model airplane owners were alerted regarding the issue found with the landing gear actuator.