Service difficulty report · Servo · Cessna 172S

Difficulty date
August 17, 2017
Submitted
August 17, 2017
Operation
General aviation
Aircraft
N560TH
Make and model
Cessna 172S
Aircraft serial
172S11668
Aircraft time
267 hours
Engine
Lyc IO360L2A
Part
Servo
Part number
RSA5AD1
Part serial
AV207971419
Condition
Defective
Location
Fuel System
Part time
267 hours
Stage of operation
LD
How discovered
C
Nature of condition
Y
Precautionary procedure
O

As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.

What was found

ON A FLIGHT AROUND THE PATTERN AT KGGG AIRPORT. DURING THE FINAL DESCENT TO LAND THE PILOT PULLED THE THROTTLE TO IDLE. THE ENGINE CONTINUED TO WINDMILL BUT BECAME VERY QUIET. WHEN THE AIRCRAFT TOUCHED DOWN AND BEGAN TO ROLL THE PROPELLER STOPPED TURNING. THE ENGINE HAD SHUTDOWN ON ITS OWN SOMEWHERE DURING THE DESCENT TO LAND. WHEN MAINTENANCE PULLED RAN THE AIRCRAFT THEY FOUND THAT THE MIXTURE VERY EXCESSIVELY RICH YIELDING A 200 + RPM RISE. THIS CAUSED THE ENGINE TO DIE AT IDLE. THE SERVO VENTURI WAS PULLED TO INSPECT BEHIND IT FOR CONTAMINATION. THIS IS A COMMON PROBLEM ON THE VERTICALLY MOUNTED RSA STYLE SERVO. THE AREA BEHIND THE SERVO VENTURI WAS COMPLETELY COVERED IN FUEL DYE FROM AVGAS. THIS CAUSED THE ENGINE TO STOP. MANUFACTURER WAS CONTACTED ABOUT THE PROBLEM AND THEY WERE ADAMANT THAT THE ISSUE WAS "OVER-PRIMING". HOWEVER, PILOTS AT THIS FLIGHT SCHOOL HAVE BEEN CAREFUL TO FOLLOW MANUFACTURERS PROCEDURES WHEN STARTING THE AIRCRAFT.

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