Date: 201310
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 50
Light: Daylight
Aircraft: M-7
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Taxi
ATC / advisory: CTAF ZZZ
Aircraft component: Tail Wheel
Component problem: Malfunctioning; Failed
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Private
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Ground Event / Encounter Ground Strike - Aircraft
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: Tailwheel bolt broke during taxi. This resulted in tailwheel detaching from spring. Taxi was at a brisk walk speed. Aircraft stopped straight ahead with no jostling or injury to pilot or passenger. The bolt in question is a 7/16' of an inch eyebolt. It broke at the shoulder. This hardware is part of a tailwheel Company's Maule aircraft Supplemental Type Certificate/ Parts Manufacturer Approval (STC/PMA) tailwheel upgrade; aftermarket tailwheel. This bolt may have failed because of fatigue or manufacturing defect; I don't know. The tailwheels on back country aircraft are a high stress area [of the aircraft] that takes a lot of pounding in dirt strip use. I will notify the tailwheel Company of this event. This may be a rare event; but if a trend were to develop there are easy fixes to helping prevent this problem. Myself; I will go to a standard hex bolt as I think it may be stronger. I will also replace this bolt with each change of the tailwheel spring; which is done periodically due to fatigue sagging.

Callback: Reporter stated there are three bolts that hold the tail spring to the aircraft with a tailwheel Company supplied 7/16' of an inch eyebolt that secures the tailwheel to the spring assembly. The 'eye' portion of the bolt at the head was used to tie down the aircraft. When he said the 'bolt broke at the shoulder'; he was referring to the area just below the bolt head where the 'eye' section is. Reporter stated while searching for information about the tailwheel; other Owner/Operators of Maule Aircraft told him the tailwheel Manufacturer had already issued a larger 1/2' half inch size bolt for attaching the tailwheel to the spring assembly that no longer had the tiedown 'eye' at the bolt head. The larger bolt is still an 'AN' type bolt; versus a generally stronger NAS type bolt. He believes that part of the problem was the use of a bushing that was inserted into the 1/2' inch hole in the spring that would hold the smaller size 7/16' inch attach bolt. The new instructions from the tailwheel Company; for attaching the tailwheel to the spring; is to remove and discard the bushing and just install the larger 1/2 half inch bolt to secure the tailwheel. No further incidences have occurred since the new installation. Reporter stated he was fortunate the tailwheel broke when his taxi speed was equal to a brisk walk and not on touchdown where he may have been faced with a ground loop incident. The tailwheel Manufacturer had previously issued rebates to Owner/Operators to offset the cost of the larger replacement bolt.



Synopsis: After a tailwheel bolt had broken during taxi; a pilot of a Maule M-7 aircraft was later informed by other Owner/Operators that the tailwheel Manufacturer had previously issued a larger bolt for attaching the tailwheel to the spring assembly.