EASA SIB NM-11-48
Learjet Inc. 31, 31A, 35, 35A, 36 and 36A aeroplanes - Wing Transverse Duct Assembly
Summary
The FAA Special Airworthiness Information Bulletin SAIB: NM-11-48 provides guidance for owners and operators of Learjet Inc. Model 31, 31A, 35, 35A (C-21A), 36, and 36A airplanes regarding inspection and potential replacement of the wing transverse duct assembly. This bulletin addresses possible restricted airflow through the duct that could reduce the anti-ice capability of the right wing leading edge. The document is informational and does not mandate regulatory action.
What Changed
This bulletin introduces awareness of a condition where the wing anti-ice transverse duct may become partially crushed, restricting hot bleed air flow to the right wing leading edge. Learjet Inc. has developed a stainless steel replacement duct to prevent distortion caused by aluminum softening. The FAA recommends compliance with specific Learjet service bulletins to inspect and replace the affected duct assemblies.
Why It Matters
Restricted airflow in the wing transverse duct can lead to ice accumulation on the right wing leading edge during flight in icing conditions, potentially compromising flight safety. Operators and maintenance personnel must be vigilant to ensure the anti-ice system functions correctly, especially since wing temperature indicators alone may not detect duct distortion. Addressing this issue helps maintain effective ice protection and safe operation of the affected Learjet models.
What To Do
Owners and operators of Learjet Model 31, 31A, 35, 35A (C-21A), 36, and 36A airplanes should inspect the wing transverse duct assembly and replace it if necessary by following Learjet Service Bulletin 31-30-6, Revision 1, and Learjet Service Bulletin 35/36-30-10, Revision 1, both dated February 12, 1999. Flight crews are advised to visually monitor wing leading edges during flight in icing conditions. No mandatory compliance deadline is specified.