This Act has been repealed and is no longer in force. It is retained for historical reference.

This mandatory Airworthiness Directive affects owners and operators of DHC‑6 Twin Otters (especially aircraft with certain wing modifications) and requires high‑frequency eddy‑current inspections of critical wing structures. Inspection timing depends on each aircraft’s modification and inspection history; some aircraft face short, specific compliance windows.

Why it matters: the checks are intended to detect fatigue cracks in wing spars and fittings before they can cause catastrophic wing failure.

2. Pre. Mod. 6/1117 Wing Assemblies

If the previous inspection of the wing main spar, attachment lug fastener holes, conducted prior to 10 August 2000, was an eddy current inspection carried out in accordance with instructions supplied by Bombardier, conduct the repeat high frequency eddy current inspection in accordance with the schedule in PSM 1-6-11 Revision 5.

b. If the previous inspection of the wing main spar, attachment lug fastener holes, conducted prior to 10 August 2000, was an ultrasonic inspection carried out in accordance with Bombardier Service Bulletin 6/525, conduct the first high frequency eddy current inspection within 1,000 hours flight time or 2,000 flights, whichever occurs first, after the last ultrasonic inspection.

Post Mod 6/1117 and Post Mod 6/1630 Wing Assemblies

If the inspection threshold for the lower wing skin, stringers and aft spar lower flange WS122 TO WS263 (ribs 8 to 20) has been exceeded or will be exceeded within 6 months after 10 August 2000, conduct the initial inspection within 500 hours flight time or 1,000 flights, whichever occurs first, but not later than 6 months after 10 August 2000.