NTSB Identification: CHI01FA180.
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Accident occurred Saturday, June 16, 2001 in La Crosse, WI
Probable Cause Approval Date: 05/30/2003
Aircraft: Potez-Air Fouga CM 170, registration: N301FM
Injuries: 2 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The airplane was destroyed on impact with terrain and post impact fire following an in-flight break up while maneuvering in the traffic pattern. The pilot and rear seat passenger were fatally injured. The accident airplane was cleared for a low approach. A record of interview with the Air Traffic Control Tower Chief stated "that when the aircraft was in front of the tower he first noticed a short vapor trail coming from the left wing tip and shortly thereafter the wing tip tank separated." A witness stated, "At approximately midway down the runway the aircraft began a 5 to 10 degrees climb at which point I observed the left wing tip fuel tank and what appeared to be a small section of the wing separate from the aircraft and smash through the tail section, which also became separated." Flight control push-pull link-rods were traced and continuity was established from the cockpits to the flight controls surfaces. The left wing was separated from the fuselage. Sections of the v-tail were found on runway 21. Both tip tanks were found in the grass area after the end of runway 21 and they were separated from their wings. The NTSB Materials Laboratory report stated, "Both of the [tip tank rear] studs were fractured flush with the exterior surfaces of the tip tanks. Examination of the fractures through the studs revealed similar features on the fractures from both tip tanks. ... Both fractures contained two diametrically opposite regions that were lighter in color and contained crack arrest positions, typical of reverse bending fatigue. On both studs fatigue initiation was from multiple initiation sites within a thread root. ... The fatigue cracking on the studs propagated through roughly 50 percent of the stud cross section before final fracture."

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The fatigue failure of the aircraft's left wing tip fuel tank rear attachment, while the aircraft was being maneuvered in a low approach, leading to the tank's in-flight separation and subsequent in-flight break up of the airplane and the aircraft's control not possible.

Full narrative available

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