Cites Flyweight Issues Which Have The Potential To To Cause Engine Failures

The FAA has issued a SAFO (Safety Alert for Operators) for Pratt & Whitney R-985-AN-14B engines following three documented engine failures caused by failed flyweight screws. These failures occurred during flight, resulting in forced landings. At the time of the failures, engine time since overhaul ranged from 2.5 hours to 671.6 hours.

According to the FAA, the engine crankshaft assemblies were overhauled by three different repair facilities. Additionally, inspections of at least four other engines have found cracked screws (P/N 23902) (pictured) and under torqued and/or improperly modified expanders used to secure the screws in the flyweights.

Additional engine models that could be affected by this issue due to similar design include all Pratt & Whitney Wasp Jr (R-985 Series) and Wasp (R-1340 Series) engines, reference image on pg 3.
The list of aircraft that use these engines include, but are not limited to:

• Air Tractor AT-301 and 401;
• Ayres Thrush;
• Beechcraft D17 and 18 series:
• Boeing-Stearman 75: de Havilland DHC-2 and DHC-3;
• Gee Bee;
• Grumman G-21 and G-164;
• Howard DGA-6, -11, -15;
• North American T-6; and
• Weatherly 201 and 620.

The FAA said it should be noted that individual crankshaft assemblies not yet installed in the above engines are also subject to this alert as well as serviceable parts in stock or in work.

Inspections of several engines, including those undergoing overhaul, have found multiple instances where steps have formed on the internal threads of the flyweight screws into which the expander is threaded securing the screw in the flyweight. These steps may impede the proper torquing of the expander which could lead to fatigue cracking of the screws and resulting failure. The FAA said it is currently not aware of any document that approves the removal of steps in the threads of the screw. If, during inspection of the screw, any of the following are found, the screw should be replaced:

• Steps in the threads of the screw;
• The surface of the screw is not smooth or has tool marks; or
• The surface treatment on the screw has been removed.

The current overhaul manual recommends a torque of approximately 1300 inch-pounds to install the screw and a recommended screw stretch of 0.001 to 0.0015 inch. If, at any time during the course of torquing the screw, the screw stretch exceeds the limitations listed in the overhaul manual, the screw should be replaced.

The agency said that certain maintenance actions accomplished between overhauls may provide visual access to the engine flyweights, i.e. cylinder replacement, etc. Owners, operators and repair facilities are urged to inspect the assemblies at those times for any signs of displacement of the screws, expanders, or flyweights. If any abnormalities are observed, the engine should be immediately removed from service and disassembled for further inspection, and the owner/operator should ensure that any affected flyweight screws and expanders are replaced. During overhaul these screws and expanders should be replaced with serviceable parts.

FMI: SAFO