Incident Summary
The airplane struck the ground short of the runway after the engine failed to respond to the throttle command during short final approach. The landing gear was down and flaps were fully extended at the time.
Pilot Actions
The pilot stated that during short final, the airplane began settling. When he added power, the engine did not respond. The pilot revealed that it was his habit to engage the low fuel boost pump for landing, even though the Pilot Owner Handbook (POH) did not require this action.
Aircraft Systems
Section 7 of the POH, which covers Airplane and System Descriptions, includes an information note: "If the engine-driven fuel pump is functioning and the auxiliary fuel pump switch is placed in the ON position, an excessively rich fuel/air ratio is produced unless the mixture is leaned." With the low (yellow) boost pump switch activated during a reduced power approach, advancing the throttle causes the boost pump to switch to high mode, potentially flooding the engine with an over-rich mixture.
The Cessna Pilot Safety and Warning Supplements booklet, under the heading "Fuel Pressure Switch Operation/Normal Auxiliary Fuel Pump Operation," states in part: "During cruise, the auxiliary fuel pump(s) may be used at any time to clear excessive fuel vapor, as evidenced by an unstable fuel flow indication; however; the auxiliary fuel pump(s) should be turned off prior to descent. Failure to turn off the pump(s) could cause a power failure at reduced throttle settings or with a rapid throttle advance due to an excessively rich mixture, especially if the throttle switch rigging or fuel pressure switch settings are out of tolerance."
Examination
A post-accident examination of the engine and related systems revealed no anomalies that would have prevented the engine from operating normally.
Conclusion
The available information indicates that the pilot's use of the auxiliary fuel boost pump during landing, contrary to the manufacturer's guidance, may have contributed to the power loss. However, the final determination rests on the official investigation.