Textron Aviation Inc. has issued a service letter requiring owners of certain 402 and 414 models to replace some of the nacelle fittings.

The letter states:

Replace nacelle fittings 5292029-9, 10, -11 -12, -21, -22, -23, and -24 Nacelle fittings with higher flight hours can fatigue and crack more easily. An undetected crack can cause the nacelle fitting to break which could result in flight instability.

The document provides instructions for determining the hours of each fitting.