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On October 12, 2006, at 1216 eastern daylight time, a Beech BE-200, N528WG, was substantially damaged while landing at St. Mary's County Regional Airport (2W6), Leonardtown, Maryland. The certificated airline transport pilot, the certificated commercial pilot, and the systems operator were not injured. Day visual meteorological conditions prevailed, and no flight plan was filed for the local test flight conducted under 14 Code of Federal Regulations Part 91.
According to the pilot, the airplane departed 2W6 to conduct a flight test in the Patuxent River restricted area at approximately 1115. After approximately 1 hour, they returned to 2W6 for a landing.
After entering the traffic pattern for runway 29, the flight crew completed the descent and before landing checklists. The checklists included verifying the landing gear position by visual observation of the landing gear indicator lights, which indicated "three green lights" and no "in-transit" lights. This was also reported over the intercom system to the systems operator, who was seated at his station in the cabin.
After flying the approach to runway 29, the airplane landed on the main gear in a "firm but normal" landing. The airplane touched down approximately 1,200 feet down the runway and within 4 to 5 feet to the right of the runway centerline. Immediately after touchdown, the pilots heard the landing gear warning horn sound intermittently for several seconds, and the right wing began to "drop." The airplane then veered to the right, so the pilot took over the flight controls and attempted to stop the right wing from dropping, but the right propeller struck the runway.
The pilot then moved both fuel condition levers to cutoff, and closed both firewall shutoff valves. The airplane continued to veer right, and the right wing contacted the unimproved grassy area to the right of the pavement, slowing the airplane to a stop. Moments later, the systems operator reported "fire right side," and all three crew members evacuated out of the main cabin door after securing the airplane.
According to Federal Aviation Administration (FAA) records, the pilot held an airline transport pilot certificate with ratings for airplane single and multi-engine land, and a type rating for the BE-200. He reported a total flight time of 7,140 hours, with 6,010 hours in multi-engine airplanes and 900 hours in the BE-200. His most recent FAA second-class medical certificate was issued on March 10, 2006.
According to FAA records, the copilot held a commercial pilot certificate with ratings for airplane single engine land, multi-engine land, and instrument airplane. He reported a total flight time of 1,100 hours, with 110 hours in multi-engine airplanes and 59 hours in the BE-200. His most recent FAA second-class medical certificate was issued on August 24, 2006.
According to FAA and maintenance records, the airplane was a twin-engine, pressurized turbo-prop, manufactured in 1979. It was licensed in the experimental category and was used for research and development by the operator.
The airplane's most recent continuous airworthiness inspection was completed on March 31, 2006, and at that time, the airplane had accumulated 11,077 total hours of operation.
A weather observation taken at Patuxent River Naval Air Station (NHK), Patuxent River, Maryland, approximately 8 nautical miles east of the accident site, at 1200, included winds from 260 degrees at 6 knots, 7 miles visibility, scattered clouds at 1,500 feet, a broken ceiling at 3,000 feet, temperature 70 degrees Fahrenheit, dew point 57 degrees Fahrenheit, and an altimeter setting of 29.62 inches of mercury.
St. Mary's County Regional Airport was a public use airport. It had one runway, oriented in an 11/29 configuration. The runway was asphalt, in good condition, and was 4,150 feet long by 75 feet wide.
WRECKAGE AND IMPACT INFORMATION
A postaccident examination of the airplane and accident site by a Federal Aviation Administration (FAA) inspector revealed that the right main landing gear had collapsed and penetrated the right main fuel tank. Skid and paint transfer marks were visible beginning at the approximate point of the airplane's touchdown and continued to where the airplane came to rest. Gouges in the pavement consistent with propeller strike marks were also evident. The right outer wing panel, right inboard wing panel and the majority of the right side of the fuselage were consumed by fire.
Examination of the airplane's landing gear system by National Transportation Safety Board investigators revealed that the left main landing gear, and nose landing gear were undamaged. The right main landing gear assembly, however, had been exposed to fire and it's landing gear actuator, actuator link, release link, overcentering guide assembly, downlock hook, upper and lower drag legs, and downlock plate were burnt and partially melted.
Further examination of the right main landing gear revealed that the downlock plate was bent and it's upper and lower drag legs were in the retracted position.
Comparison of the right main landing gear assembly to the undamaged left main landing gear assembly revealed, that the downlock plates were of different configurations and both had been installed with their beveled surfaces facing aft.
During examination of an exemplar airplane, it was discovered, however, that this installation differed with the exemplar and a review of the manufacturer's engineering drawings showed that the accident airplane's downlock plates should have been installed with their beveled surfaces facing forward.
TESTS AND RESEARCH
Materials Laboratory Examination
Examination of the main landing gear components by the Safety Board's Materials Laboratory revealed that, the throat of the right main downlock hook where the downlock plate was trapped during operation, was generally intact and had retained its approximate original shape.
Cleaning of the downlock hook revealed horizontal contact marks extending across the lower portion of the face, and "raised lips" (deformation), at the inboard and outboard edges. The face markings and deformations were consistent with forceful sliding contact with the downlock plate.
Measurements made with the downlock plates installed as found on the accident airplane revealed, that the mutual contact area between the downlock plate and the throat of the downlock hook was less than 0.05 inch.
When the lock plates were installed in accordance with the manufacturer's engineering drawings, the engagement area between the downlock plate and the downlock hook increased to about 0.25 inch, which was approximately the full depth of the downlock hook throat.
Maintenance Records Examination
Examination of the accident airplane's maintenance records revealed that the landing gear and actuator assemblies had accumulated 38.7 hours of operation at the time of the accident. They had been purchased from an FAA approved repair station and installed on the accident airplane by the operator in accordance with the manufacturers approved maintenance program.
According to the repair station's records, all of the overhauled components had been inspected and assembled in accordance with the manufacturer's component maintenance manual (CMM).
Review of the manufacturer's CMM revealed that, no guidance regarding downlock plate orientation during installation was included.
On December 16, 2006, the repair station advised the Safety Board that they notified their customers that main landing gear downlock plates may have been incorrectly installed at their facility and inspected all landing gear assemblies that were in their possession.
On November 1, 2007, the airplane manufacturer revised their component maintenance manual to, "ensure that the lock plate is installed with the beveled edge down," and to ensure "the end of the lock plate makes contact with the back of the downlock hook."