NYC01LA160

The pilot was performing takeoffs and landings. After each landing, he would back-taxi on the runway for the next evolution. While back-taxiing with the tail raised, and a quartering tailwind of 7 to 8 knots, he encountered a wheel shimmy. He dampened the shimmy with rudder input, after which the airplane abruptly departed the runway to the right. The left main landing gear collapsed, and the left wing and propeller contacted the ground. Metallurgical examination of the failed landing gear brace revealed that it had failed in compression, consistent with the ground loop, and there was no evidence of fatigue or corrosion. The strut was the proper material, and its hardness was within specification. The diameter of the strut was correct; however, it wall thickness was thinner than specified. Computations indicated the lower wall thickness reduced the overall bending strength of the strut by 24 percent.

On June 30, 2001, at 1844 eastern daylight time, a homebuilt Avid Mark IV, N1968N, was substantially damaged during a high speed taxi at the Salisbury-Ocean City Wicomico Regional Airport (SBY), Salisbury, Maryland. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed for the personal flight. No flight plan had been filed for the local flight that was conducted under 14 CFR Part 91.

According to the pilot:

"A series of practice aborted takeoff were being executed at SBY: the craft was rotated into the air from R/W 23 at its best rotation speed, 65 knots, then flown down the runway at approx. 20 feet off the deck to a landing at the far end of the runway.

After approx. the sixth take-off and landing set, a failure of the left landing gear occurred while back-taxiing (at high speed) along RW 23, approximately 300 yards from the end of RW 23.

The aircraft shuddered momentarily, very briefly, then continued straight ahead for approximately 3 seconds. After which time, the craft veered violently to the starboard.

I pulled back power just as the craft left the runway and entered the grass. Next the left gear collapsed completely and the craft scraped its belly in the grass, breaking off the prop. I disconnected the seatbelt/ shoulder harness, turned off the fuel and master switch and scrambled out the passenger's door (mine was jammed shut 'cause the craft had collapsed on its port side).

Visibility was excellent, it was sunny and warm. There were gusts from the S.E. at approx 10 knots."

In a follow-up telephone interview, the pilot reported that he was able to dampen the shudder for a moment with rudder pedal input, after which, the airplane initiated a violent right turn. The pilot further reported that he had built the airplane. During its initial test flight in June 1999, another pilot landed it hard, and both landing gear collapsed. The landing gear were rebuilt and sections re-welded. This included the area of the fracture.

The pilot and an inspector from the Federal Aviation Administration (FAA), reported that the brace on the left main landing gear had fractured near its connection to the fuselage. Additional damage included bent longerons on the left side of the fuselage, and bending to the left wing and left wing flaperon.

According to archived weather reports for SBY, on June 30, at 1754, the winds were from 210 degrees at 8 knots, and at 1854, the winds were from 210 degrees at 7 knots.

According to the owner of Avid Aircraft, each main landing gear strut was connected to the outboard edge of the lower fuselage, and angled outward. Each main landing gear strut was fixed in place with a brace, which connected to the lower center of the fuselage, between the landing gear and terminated near the wheel. If the landing gear were exposed to a hard landing, each brace would be exposed to tension. If the airplane made an abrupt turn, or ground looped, the brace on the outboard landing gear was placed in compression, and the brace on the inboard landing gear was placed in tension.

The failed brace was examined by the Safety Board Materials Laboratory in Washington, DC. According to the metallurgists factual report:

"...The center bend in the brace and the direction of bending associated with the fractures were consistent with buckling of the brace from excessive compression loads."

Further metallurgical examination of the failed brace revealed the wall thickness was thinner than specified. The report stated:

"...the critical buckling load for the accident airplane's main landing gear brace was about 76 percent of the critical buckling load expected for a typical brace."

The pilot reported his total flight experience as 443 hours, with 21 hours in type, including 16 hours in the preceding 90 days which included 7 hours in type.