ANC13LA016

The flight instructor was demonstrating a short field, three-point landing. The touchdown was normal, but during the landing roll a gust of wind pushed the airplane, and it began to turn to the right. The instructor applied left brake in an attempt to correct for the right turn, and the airplane’s left main landing gear broke. As the broken gear leg dug into the runway, the airplane pivoted 180 degrees to the left, and the left wing struck the runway. The airplane sustained substantial damage to the left wing and fuselage. The flight instructor stated that during the last annual inspection, about 4 months before the accident, he observed corrosion on the main landing gear legs and ground it off using a hand-held grinder. The service manual specified to carefully remove any rust by light sanding; the sanding must blend the damage into the adjacent area in an approximate 20:1 ratio. Examination of the landing gear revealed evidence of the improper maintenance and corrosion damage, which weakened the gear and led to fatigue cracking and an overstress fracture.

On December 13, 2012, about 1409 Alaska standard time, a tailwheel-equipped Cessna 150C airplane, N1901Z, sustained substantial damage while landing at the Juneau International Airport, Juneau, Alaska. The airplane was being operated as a visual flight rules (VFR) instructional flight under the provisions of Title 14, CFR Part 91, when the accident occurred. The student pilot, and the airline transport rated flight instructor (CFI) were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on December 14, the CFI stated that the accident flight originated at the Juneau International Airport, for a local flight to practice stop-and-go landings. At the time of the accident he was demonstrating a short field, three-point landing. He said that the touchdown was normal, but during the landing roll a gust of wind pushed the airplane, and it began to turn to the right. He applied left brake in an attempt to correct for the right turn, and the airplane’s left main landing gear broke. As the broken gear leg dug into the runway, the airplane pivoted 180 degree to the left, and the left wing struck the runway. The airplane sustained substantial damage to the left wing and fuselage. The CFI, who is also a certificated airframe and powerplant (A & P) mechanic, stated that during the annual inspection in August, he observed corrosion on the main landing gear legs. The corrosion was ground off with a hand held grinder, and Zinc Chromate Primer applied. The Cessna 100 Series Service Manual, Section 5-5A Corrosion Control on Landing Gear Springs specifies in part: Carefully remove any rust by light sanding; the sanding must blend the damage into the adjacent area in an approximate 20:1 ratio. The fracture face contained a crescent-shaped fracture on the upper forward surface which is consistent with features of fatigue cracking. The remaining fracture surface contained a coarse grainy appearance, clear chevron markings, and a shear lip, which are consistent of an overstress fracture. Corrosion damage and grinder marks were also present on the surfaces of the left landing gear leg. The closest weather reporting facility is Juneau International Airport. At 1353, an aviation routine weather report (METAR) at Juneau, Alaska, reported in part: wind, calm; visibility, 10 statute miles; light rain; few clouds at 2,000 feet; broken clouds at 3,900 feet; broken clouds at 5,000 feet; temperature, 36 degrees F; dew point 32 degrees F; altimeter, 29.44 inHG.