Accident Details
A Hiller FH-1100 was destroyed upon impact with terrain following the separation of a tail rotor blade during cruise flight. The main wreckage was located, and the separated tail rotor blades were found at a distance: Blade 'B' was discovered 700 feet south of the main wreckage, with the separation occurring at 1/4 span from its root. Blade 'A' was located 850 feet south of the main wreckage.
Maintenance History
The tail rotor blades had been overhauled and were later removed for blade delamination on July 14, 1986. Inspection of the blades revealed that the inside surfaces of Blade 'A's' skin showed longitudinal streak patterns of debris. The skin trailing edge closure bond contained an adhesive that was bright purple in color.
Adhesive Usage
During the period 1967–1982, tail rotor blades were bonded with FM1000, a cream or off-white colored adhesive. Since 1982, FM1000 was used to bond the skin and doubler, while FM73, an orange-brown colored adhesive, was used between the root fitting and doubler. The bright purple adhesive found on Blade 'A' did not match either of these standard adhesives.
Rivet and Hole Condition
Examination of the rivet holes in the skin showed wear on the skin surfaces under the upset heads of the rivets. No wear was visible under the manufactured heads. The rivet holes were not round and appeared to have two overlapping diameters, consistent with double drilling.
Manual and Inspection Guidance
The Hiller FH1100 Overhaul Manual, under Tail Rotor Assembly, Repair - Tail Rotor Blade Assembly, states: "...Replacement of skin, doubler or rib ... is not permitted." The Hiller FH1100 Inspection Guide describes inspections of the tail rotor blades during preflight, 100-hour inspection, and 300-hour inspection.