Accident Details
On September 26, 2016, at about 1420 Alaska daylight time, a tailwheel-equipped Helio Courier H-250 airplane, registration N6324V, sustained substantial damage during the landing roll at the Lake Hood Seaplane Base in Anchorage, Alaska. The certificated commercial pilot was not injured. The aircraft was operated by a private individual under 14 CFR Part 91 on a visual flight rules flight, and visual meteorological conditions prevailed. The flight originated from a private airstrip near Igiugig, Alaska, around 1200.
Pilot Report
The pilot stated in a written report that after an uneventful touchdown on the dry, gravel surface of runway 32, a medium vibration was felt as the brakes were applied. During the landing roll, both main landing gear legs sheared off. The propeller struck the runway, and the airplane came to rest on the bottom of the fuselage.
Aircraft and Landing Gear Information
The airplane sustained substantial damage to the fuselage. Postaccident inspection revealed that both main landing gear legs had fractured below a support bracket at the attachment points. The legs (left side part number 250-040-451-0; right side part number 250-040-451-1) were constructed of 1/8-inch steel, molded and welded into a 2-inch-square steel tube, and covered by a contoured fairing. The pilot reported the legs were manufactured in 1966, with about 3,500 total hours, 15,000 cycles, and 15 hours since the last inspection.
In a later statement, the pilot noted that he could not determine when the main landing gear was last inspected, as the legs were changed in 2013 for ski-wheel use, and he was unsure if a dye penetrant inspection was performed. The installed legs came from another aircraft with about 3,500 total hours.
Postaccident Examination
The main landing gear legs were sent to the NTSB Materials Laboratory in Washington, D.C. Examination revealed that both legs were fractured through the square tube section between 29 and 30 inches above the axle centerlines. Multiple fatigue regions were present in the vertically oriented, aft walls of both legs, particularly near the upper and lower corners. All fatigue regions initiated at multiple sites on the outer (aft) surfaces of the tube and propagated inward through the wall.
Pilot Recommendations
In the NTSB accident reporting form, the pilot recommended that the main landing gear be checked by specialists at annual inspections, especially when converting between ski-wheels and wheels, as hard landings and previous cracks can be difficult to detect.
Meteorological Information
At 1353, the Lake Hood Seaplane Base METAR reported: wind from 310 degrees at 5 knots; visibility 10 statute miles; overcast ceiling at 5,500 feet; temperature 46°F; dew point 36°F; altimeter 29.89 inHg.
Related Information
The NTSB materials laboratory examination report is in the public docket. A prior accident (ANC05LA097) involved a similar fracture of a right main landing gear leg on a Helio H-250. The Federal Aviation Administration Advisory Circular 43.13-1B (2001) provides guidance on landing gear inspection, stating that the entire structure should be examined for cracks, nicks, and other stress concentrations.