Monday, December 19, 2016

Stinson 108-3 Voyager, N812C: Accident occurred December 16, 2016 in Ionia County, Michigan

The National Transportation Safety Board did not travel to the scene of this accident. 

Aviation Accident Preliminary Report - National Transportation Safety Board:

FAA Flight Standards District Office: GRAND RAPIDS, MICHIGAN.

NTSB Identification: CEN17LA057
14 CFR Part 91: General Aviation
Accident occurred Friday, December 16, 2016 in Ionia, MI
Aircraft: STINSON 108-3, registration: N812C
Injuries: 1 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On December 16, 2016, about 1045 eastern standard time, a Stinson model 108-3 single-engine airplane, N812C, equipped with snow skis, was substantially damaged while landing at Ionia County Airport (Y70), Ionia, Michigan. The private pilot, the sole occupant, was not injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed for the flight that departed Lowell City Airport (24C), Lowell, Michigan, about 1030.

The pilot reported that shortly after takeoff from a snow covered runway he heard a thump and subsequently saw that the left main landing ski tip had rotated up, past vertical, and was in contact with the left wing strut. He decided to land at nearby Y70 because he anticipated requiring assistance upon landing and the departure airport was unmanned. Additionally, Y70 had a snow covered turf runway, south of the paved runway 9/27, that was typically used for glider operations. The pilot reported that upon touchdown, the left main landing ski separated from the axle, the left gear leg dug into the snow, and the airplane rapidly decelerated before it nosed over. The right wing, left wing strut, and vertical stabilizer were substantially damaged during the accident.

As designed, the main landing skis are supported by two 5/32 inch braided steel cables and bungee/shock cords. Both ends of the 5/32 inch steel cables are terminated with a thimble-eye and compressed/swaged plain copper oval nicropress sleeve (No. 18-4-P). On the accident airplane, the forward and aft support cables had pulled through their respective nicropress sleeves where the cables attached to the left ski's tip and tail. The nicropress sleeves for the left ski tip and tail attachments were not located during the investigation. However, a visual examination of the remaining nicropress sleeves, located where the support cables attached to the left landing gear leg, appeared to be inadequately compressed. Additionally, a visual inspection of the right main landing ski cables also revealed inadequately compressed nicropress sleeves. The width of the remaining nicropress sleeves, as measured with a dial-caliper, were between 0.440 and 0.446 inch.

According to manufacturer specifications, when properly formed, the width of a 5/32 inch nicropress sleeve should be less than 0.395 inch. A test cable eye was fabricated using 5/32 inch braided steel cable and two plain copper oval nicropress sleeves (No. 18-4-P). The first nicropress sleeve was compressed using a proper 5/32 inch swage tool. The other test sleeve was compressed using a larger 3/16 inch swage tool. The width of the properly formed test sleeve, using a 5/32 swage tool, measured 0.383-0.386 inch. The width of the other test sleeve, using a 3/16 swage tool, measured 0.442-0.452 inch. 

The pilot reported that the accident airplane was typically equipped with snow skis during the winter snow seasons. In February 2009, he purchased the main landing skis, Federal Aircraft Works model A-2500A, from a private individual. The skis were purchased used with an undocumented service history. The skis were purchased as complete assemblies, which included all cables, bungees, brackets, and hardware appropriate for a Stinson model 108-3 installation. The forward and aft support cables were already fabricated and installed on the skis when they were delivered to the pilot. Additionally, the pilot reported that the support cables were not repaired or replaced while he owned the skis.

On December 14, 2016, the pilot, who was also an aviation mechanic, installed the main landing skis for the 2016/17 winter snow season. According to an airframe logbook entry, the main landing skis were installed per manufacturer's drawing No. 11R955/AB. The accident occurred during the first flight since the skis were installed for the season.

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