New LAA Alert for all Rotax 900 series engines

The LAA has issued Alert A-04-2024 – Highlighting loose and broken engine mounting bolts on Rotax 900 series engines

A recurring problem with Rotax 912/914 engines, equally applicable to the newer 915 and 916 models, is of the four M10 bolts that attach the engine’s crankcase to the engine mounting frame becoming loose in service.

Most manufacturers call for the bolts to be wire-locked in place. However, in the case of the Rotax engine mounting bolts, it seems that the bolts are coming loose not because the bolts are undoing and backing off on their threads, but because of the joint faces become imprinted over time through creep, corrosion or fretting, allowing the tension in the bolt to be lost and the joint to become loose.

These problems in the field are a reminder that where it’s critical that a bolt be torqued up, this should be checked at intervals (at least annually, we’d suggest) by undoing the locking and re-torquing them, before replacing the locking wire. Be sure this check is included in your aircraft’s maintenance schedule. DO NOT RELY ON A BOLT BEING WIRE LOCKED TO BE SATISFIED THAT THESE CRITICAL BOLTS ARE STILL TIGHT.