Cirrus Design Corp SR22T N707DF accident near San Diego, California

Probable cause

The pilot's exceedance of the airplane's critical angle of attack during an attempted return to the runway following a total loss of engine power after takeoff, which resulted in an aerodynamic stall. Contributing to the accident was the excessive amount of fuel being delivered to the engine for reasons that could not be determined based on the available information.

NTSB analysis

The private pilot was taking off in the airplane when witnesses heard the airplane lose engine power at low altitude and described a sequence of events consistent with an aerodynamic stall/spin. Data retrieved from onboard the airplane recorded 47 power cycles, including the accident takeoff. The data revealed an abnormally high fuel flow, about 46 gallons per hour (gph), when takeoff power was applied, reaching 50.1 gph as the airplane entered the initial climb. About 300 ft above ground level (agl), the airplane experienced a total loss of engine power and began to decelerate and roll to the right. The airplane then entered a steep left bank and nearly vertical nose-down attitude as it descended to ground contact. The final data point at 50 ft agl indicated that the airplane was in an 81° nose-down pitch attitude and a 157° (inverted) left roll. The data is consistent with the pilot attempting to return to the runway following a loss of engine power at low altitude and an aerodynamic stall/spin when the pilot exceeded the airplane's critical angle of attack during the turn.

Examination of the engine revealed signatures consistent with an excessively rich fuel/air mixture. The fuel manifold and engine-driven fuel pump were removed from the engine and installed onto a slave engine for a test run, during which the slave engine began to surge when the power was increased to 2,300 rpm; the fuel pressure indicated 234 psi (about 39 gph); a nominal value was 210-220 psi. The engine-driven fuel pump adjustment screw was adjusted in the lean direction, and the engine operated within normal parameters; however, when the test cell fuel boost pump was turned on, the engine lost total power.

The airplane was equipped with an electric fuel boost pump that could be manually activated by the pilot via a cockpit switch. The pump had two modes; the BOOST position supplied an additional 4-6 psig at 19 gph to the engine and was used for vapor suppression when required and during takeoff, climb, landing, and when switching fuel tanks. The HIGH BOOST/PRIME position provided a capacity of 42 gph at 16 psig with a maximum full relief (no flow) pressure of 23 psig to the engine, and was used for priming the engine before start and suppressing vapor formation at flight altitudes above 18,000 ft with hot fuel.

It is likely that the excess fuel being delivered to the engine during the initial climb resulted in the total loss of power; however, the reason for the excessive fuel flow values could not be determined. According to the manufacturer, the initial fuel flow adjustments occurred at the factory about 4 months before the accident and before the pilot took delivery of the airplane. There were no maintenance logbook entries to indicate that the fuel flow had been adjusted since that time. The data did not indicate a gradual increase in fuel flow values over time; therefore, it is unlikely that the engine-driven fuel pump adjustment screw was becoming loose. It is possible that the pilot placed the fuel boost pump in the HIGH BOOST/PRIME position before takeoff, which would have increased fuel flow to about 42 gph, but this scenario does not account for the 50-gph fuel flow value reflected in the data. (The fuel boost pump position was not a recorded parameter and the position of the switch at the time of takeoff could not be determined.) Thus, based on the available information, the reason for the fuel flow rates being so high during the takeoff could not be determined.

Text from the NTSB. Open the NTSB docket for WPR18FA093 for the full record.