Focus Is On Flap Motor Mounting Studs

The FAA has issued a Special Airworthiness Information Bulletin (SAIB) notifying owners and operators of procedures to replace one configuration of the flap motor mounting studs with an improved configuration, and to inspect for and correct cracking and separation of the flap motor mounting studs, which if left uncorrected, could result in loss of control. The SAIB applies to Air Tractor, Inc., Models AT-602, AT-802, and AT-802A airplanes. However, AT-802/AT-802A models with part number 71112-1 flap actuator installed are not affected.

According to the SAIB, an incident occurred where the two mounting studs attaching the motor to the flap actuator assembly cracked, resulting in separation of the flap motor and loss of flap control on one of the above-referenced airplanes. In addition, the separated motor fell downward and interfered with the aileron controls. Other incidents of cracked mounting studs have also been reported. Cracks were only reported with one of the three possible stud configurations installed.

To address this, Air Tractor issued Service Letter (SL) #375, dated April 9, 2019, which describes procedures for inspection of the flap motor mounting studs for cracks, and for replacement of mounting studs found to be cracked or susceptible to cracking. SL #375 describes the stud configuration that is susceptible to cracking, as well as the acceptable replacement configurations.

The FAA recommends that owners and operators perform a one-time inspection of the flap actuator motor before further flight per Section 5, Action, of Air Tractor Service Letter #375, dated April 9, 2019.

In the event cracked studs, or stud configurations susceptible to cracking, are found installed, the FAA recommends that owners and operators replace the flap motor mounting studs with one of the other two acceptable stud configurations described in Section 4, Summary, of Air Tractor Service Letter #375, dated April 9, 2019. Instructions for replacement should be performed in accordance with the Section 6, Replacement Procedure, detailed in Air Tractor Service Letter #375, dated April 9, 2019.

(Source: FAA. Image from file)

FMI: SAIB