What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
While in cruise flight at ~500 AGL, on return trip to base after about 1.6 hrs of flight, pilot heard fluctuation in engine and activation of low rotor horn. He tried once to ensure throttle was full open and reduced collective but horn remained so he entered full autorotative descent and landed in swampy ground with no damage or injuries. After landing, engine was still at idle, so shutdown initiated. Aircraft sank to belly in soft ground so restart and runup was not attempted until aircraft raised and placed on shoring. D.o.m. arrived and ran up aircraft with no faults noted. A/c run at full power and hovered in place for 5 hours with no interruptions or anomalies. Aircraft released for recovery to home station. After another 5 hour flight home with no anomalies. Servo, manifold, fuel system inspected with no faults or contamination in any part. Discussion with pilot showed possibility that low rotor horn was single indication and that engine still fully functioning, but due to proximity to ground and lack of time or altitude to troubleshoot, he had initiated autorotation automatically. Maintenance stated second set of points in right mag that provide low rotor signal may have been interupted causing erroneous low rotor indication while none was present. Tear down and ispection of fuel and mag systems higlighted no readily apparent faults. Filters inspected again, valve guide check completed, mags bench tested with no faults found. A slight binding condition noted in fuel servo throttle lever just above midrange. Servo replaced out of abundance of caution and suspect unit sent to manufacturer for teardown analysis. Aircraft returned to service.
As the FAA filed it
WHILE IN CRUISE FLIGHT AT ~500 AGL, ON RETURN TRIP TO BASE AFTER ABOUT 1.6 HRS OF FLIGHT, PILOT HEARD FLUCTUATION IN ENGINE AND ACTIVATION OF LOW ROTOR HORN. HE TRIED ONCE TO ENSURE THROTTLE WAS FULL OPEN AND REDUCED COLLECTIVE BUT HORN REMAINED SO HE ENTERED FULL AUTOROTATIVE DESCENT AND LANDED IN SWAMPY GROUND WITH NO DAMAGE OR INJURIES. AFTER LANDING, ENGINE WAS STILL AT IDLE, SO SHUTDOWN INITIATED. AIRCRAFT SANK TO BELLY IN SOFT GROUND SO RESTART AND RUNUP WAS NOT ATTEMPTED UNTIL AIRCRAFT RAISED AND PLACED ON SHORING. D.O.M. ARRIVED AND RAN UP AIRCRAFT WITH NO FAULTS NOTED. A/C RUN AT FULL POWER AND HOVERED IN PLACE FOR 5 HOURS WITH NO INTERRUPTIONS OR ANOMALIES. AIRCRAFT RELEASED FOR RECOVERY TO HOME STATION. AFTER ANOTHER 5 HOUR FLIGHT HOME WITH NO ANOMALIES. SERVO, MANIFOLD, FUEL SYSTEM INSPECTED WITH NO FAULTS OR CONTAMINATION IN ANY PART. DISCUSSION WITH PILOT SHOWED POSSIBILITY THAT LOW ROTOR HORN WAS SINGLE INDICATION AND THAT ENGINE STILL FULLY FUNCTIONING, BUT DUE TO PROXIMITY TO GROUND AND LACK OF TIME OR ALTITUDE TO TROUBLESHOOT, HE HAD INITIATED AUTOROTATION AUTOMATICALLY. MAINTENANCE STATED SECOND SET OF POINTS IN RIGHT MAG THAT PROVIDE LOW ROTOR SIGNAL MAY HAVE BEEN INTERUPTED CAUSING ERRONEOUS LOW ROTOR INDICATION WHILE NONE WAS PRESENT. TEAR DOWN AND ISPECTION OF FUEL AND MAG SYSTEMS HIGLIGHTED NO READILY APPARENT FAULTS. FILTERS INSPECTED AGAIN, VALVE GUIDE CHECK COMPLETED, MAGS BENCH TESTED WITH NO FAULTS FOUND. A SLIGHT BINDING CONDITION NOTED IN FUEL SERVO THROTTLE LEVER JUST ABOVE MIDRANGE. SERVO REPLACED OUT OF ABUNDANCE OF CAUTION AND SUSPECT UNIT SENT TO MANUFACTURER FOR TEARDOWN ANALYSIS. AIRCRAFT RETURNED TO SERVICE.
Other reports on N74381 · 1
Matched to the same aircraft by N-number and date.