Airworthiness Directives; Thrush Aircraft, Inc. Model 600 S2D and S2R (S-2R) Series Airplanes

The FAA is adopting a new airworthiness directive (AD) to supersede AD 2003-07-01, which applies to certain Thrush Aircraft, Inc. Model 600 S2D and S2R (S-2R) series airplanes (type certificate previously held by Quality Aerospace, Inc. and Ayres Corporation). AD 2003-07-01 currently requires you to repetitively inspect the \1/4\- inch and \5/16\-inch bolt hole areas on the lower wing spar caps for fatigue cracking; replace or repair any lower wing spar cap where fatigue cracking is found; and report any fatigue cracking found. This AD is the result of the analysis of data from 112 cracks found in the last 8 years on similar design Model 600 S2D and S2R (S-2R) series airplanes, and FAA's determination that an immediate initial inspection and more frequent repetitive inspections are necessary to address the unsafe condition for certain airplanes. Consequently, this AD would require you to increase the frequency of the repetitive inspections on Groups 1, 2, 3, and 6 airplanes; and decrease the hours time-in-service (TIS) for the initial inspection on Group 2 airplanes. We are issuing this AD to prevent lower wing spar cap failure caused by undetected fatigue cracks. Such failure could result in loss of a wing with consequent loss of airplane control.