Accident Summary
On September 11, 2024, at about 0940 mountain daylight time, a Cessna 172S airplane, registration N20747, was substantially damaged during a forced landing to a golf course near Englewood, Colorado. The flight instructor was not injured, and the student pilot sustained minor injuries. The airplane was being operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
The pilots were conducting touch-and-go landings on runway 17R at Centennial Airport (APA) in Englewood. During climbout for the traffic pattern, at approximately 200 feet above ground level, they experienced a partial loss of engine power. The instructor reported that the tachometer initially indicated 2,100 rpm, then dropped to 1,600 rpm. He executed a forced landing to a golf course. During the landing roll, the nose landing gear collapsed, and the airplane came to rest inverted.
Maintenance History
A review of maintenance logbook entries revealed that on September 5, 2024, about one week before the accident, another pilot had reported that the airplane “was only getting 2,000 rpm at max power and was backfiring constantly in the run-up.” Maintenance personnel subsequently found that the engine operated satisfactorily during a ground run-up. The airplane was then flown daily without any further reported engine problems until the accident takeoff.
Post-Impact Examination
A postimpact examination of the engine found no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. However, during a bench test of the engine’s fuel injection servo (AVStar part number LFR-NNSS5), fuel flow was below the minimum service limit at most test points. Upon disassembly of the servo, a thick blue liquid consistent with a fuel-oil mixture was found in the venturi chambers. Oil residue was noted in the hex plug and air diaphragm, the spring and stem assembly, and the air passage to the air diaphragm.
The AVStar LFR-NNSS5 is a variant of the RSA-5AD1 fuel injection servo and was mounted in an updraft configuration on the accident airplane. AVStar service bulletin AFS-SB10, “Fuel Servos Installed in an Updraft Configuration,” applicable to RSA-5AD1 servos, states that there have been occasional reports of servo-equipped engines exhibiting gradually deteriorating idle, difficulty starting, and/or cold engine acceleration performance. It notes that these engines may have the servo mounted in an updraft or nearly updraft configuration. Close inspection may reveal oily contaminant in the bore of the servo that is green/blue in color, and this contaminant can migrate into the air section of the regulator.
Precision Airmotive service information letter SIL RS-40, “Service Information For RSA-5 Series Fuel Injection Servos Installed in Updraft Configuration,” similarly notes reports of reduced engine performance and recommends inspection of fuel injection servos for contamination if these problems are experienced.
Service Bulletins and Procedures
The flight school’s maintenance personnel stated they were aware of AVStar AFS-SB10 and Precision Airmotive SIL ARS-40 and routinely inspected their airplanes that had any symptoms listed in AFS-SB10. Additionally, they reported that they caution their pilots against over-priming the engine during engine starts.