FACTORY ALERT

1. Exhaust System Failures Models 17-30, 17-31, 17-30A, 17-31A & 17-31ATC

A 1970 Model 17-30A had a very serious accident a few months ago.  The pilot was approaching his destination airport when he noticed a green nose gear down and locked light before he put the landing gear down. HHe cycled his landing gear but the nose landing gear light remained on. He noticed smoke near the master switch so he turned it off.  The engine quit shortly thereafter.   The pilot flew the airplane into a wooded area; the airplane/cabin remained intact but the fuselage caught on fire after impact and was destroyed. The pilot and passenger were able to climb out of the wreckage without serious injury. 

We were asked to participate and were made party to the NTSB investigation.  The investigation essentially determined that the left exhaust system failed at the weld between the ball joint and aft muffler flange, releasing hot exhaust gasses into the engine compartment.  The airplane did not have the SK1067: Rerouting Right Magneto “P” Lead installed.  The hot exhaust gasses quickly melted the insulation of the “P” Leads which shorted to ground, shutting down the engine.  The false indication of the nose landing-gear down/locked light also was most likely caused by the down limit switch shorting to another wire at 12 volts. 

The existing AD 76-23-03 R1 requires that Ball Joints be inspected for free motion and the mufflers be inspected for cracks at every 100 hour / Annual Inspection whichever occurs first.  The older mufflers were assembled with internal welds which are difficult to inspect unless the Mufflers are disassembled; the AD does not require disassembly.  The NTSB therefore asked the FAA to reissue the AD to require a more detailed inspection including disassembly of the mufflers.  We wrote a new Service Letter B110: Exhaust System Inspection & Rerouting Magneto “P” Leads which the FAA has recently approved and is attached.  The AD will be going thru the NPRM process and will probably not be released until later this year. We are releasing the service letter now so that owners and pilots can become aware of this issue.  We are assembling an inventory of SK1072 kits for the "P" lead portion of SL B110 and muffler parts to support your aircraft.