EASA SIB CE-18-06: Air Tractor AT-400/-500/-600/-800 Aeroplanes - Rudder Control System

What to do

Affected owners and operators should inspect the vertical fin rear spar bolts by removing the surrounding skin before the next flight to check for damage. At the next annual inspection, they should replace the six bolts and nuts with NAS1303 bolts and MS21042-3 nuts following the procedures in Snow Engineering Co. Service Letter #359, Revision A, dated November 29, 2017. Any findings of damaged bolts should be voluntarily reported to the FAA contacts provided in the bulletin.

Summary

The FAA Special Airworthiness Information Bulletin SAIB: CE-18-06 addresses an airworthiness concern for Air Tractor, Inc. Models AT-401B, AT-402B, AT-502A, AT-502B, AT-504, AT-602, AT-802, and AT-802A with specific serial numbers prior to certain limits. The bulletin focuses on the rudder control system, specifically the bolts and nuts through the vertical fin rear spar. It provides information and recommendations but does not mandate compliance.

What changed

SAIB CE-18-06 introduces recommendations for inspecting and replacing the six bolts and nuts at the vertical fin rear spar attach point on affected Air Tractor models. It references Snow Engineering Co. Service Letter #359, Revision A, which provides detailed replacement procedures following reported bolt failures. The bulletin does not impose mandatory regulatory action but advises proactive maintenance steps.

Why it matters

This bulletin is important because failure of the vertical fin rear spar bolts can lead to rudder control issues, potentially affecting airplane handling and safety. Operators and maintenance personnel need to be aware of this concern to prevent in-flight control difficulties. Early detection and replacement of these components help maintain airworthiness and reduce the risk of control system failures.