AD 57-25-02

57-25-02 HELIO: Applies to Model H-391B Aircraft Serial Numbers 001 Through 055.

Compliance required as indicated.

Cracks have been found in the fin front spar underneath the steel attachment fittings holding the stabilizer to the fin. Cracks were also discovered in the flanges of the fins nose ribs second and third from the bottom. To preclude possible failure of the fin spar, the following inspections and rework are required:

1. Aircraft with less than 400 hours total time.

(a) Inspect visually for cracks the fin front spar and lower nose ribs within the next 100 hours of operation and every 100 hours thereafter until reinforced as described in Helio Service Bulletin No. 17 or equivalent.

(b) If cracks are found they must be stopdrilled and the parts reinforced prior to further flight.

(c) If no cracks are found reinforcement of the fin front spar and lower nose ribs attachments is required prior to the accumulation of 400 hours total time.2. Aircraft having 400 hours or more total time.

(a) Visual inspection and reinforcement are required within the next 25 hours flight time. If any cracks are found, they should be stop-drilled prior to adding the reinforcements.

(Helio Service Bulletin No. 17 covers this subject.)