The Federal Aviation Administration (FAA) has issued an Airworthiness Directive regarding Air Tractor AT-802 and AT-802A aircraft equipped with Wipaire, Inc. Wipline 10000 Amphibian Floats, as detailed in Supplemental Type Certificate (STC) # SA01795CH. This directive also covers previously float-equipped planes that have been converted back to landplane configuration under the same STC.
A routine maintenance inspection on an Air Tractor Model AT-802 aircraft unveiled a hairline crack in the flange of the right forward horizontal stabilizer spar. This particular airplane was fitted with the aforementioned STC and is employed in fire-fighting operations, which can accelerate the propagation of crack growth. Among the 144 Air Tractor Model AT-802 and AT-802A airplanes featuring this STC, 45 have undergone inspections, with 24 of them revealing cracks in at least one forward horizontal stabilizer spar. The cracks are situated within the bend radius of the forward horizontal stabilizer spar, precisely at the STC finlet mounting positions.
This AD, effective from August 9, 2023, mandates the inspection of both forward horizontal stabilizer spars for cracks, the replacement of any cracked ones, and the submission of inspection findings to the FAA. Wipaire, Inc. Service Letter 253, Revision B, dated July 27, 2023, outlines the inspection procedures and compliance timelines. Depending on the installed STC configuration, compliance must be observed within a window of 3 to 15 days or 24 hours of time-in-service (TIS), whichever comes later. Subsequent inspections are required every 200 hours TIS.
The immediate implementation of this AD by the FAA stems from the potential risk of structural failure in the forward horizontal stabilizer spars, which could result in a loss of control over the aircraft's horizontal tail. The airplanes equipped with the specified STC are utilized for fire-fighting tasks, subjecting them to frequent high-repetitive fatigue loads in this specific region due to their high utilization rate. You can access the full AD document here.
