Logan, UT, USA
N802PS
Czech Sport AIrcraft Sport Cruiser
The student pilot was making his second solo cross-country flight. He completed the first leg and shut down the engine. When he restarted the engine to begin the next leg of the flight, it momentarily lost power during the magneto check, and he shut it down. After consulting his flight instructor by cell phone, he again started the engine, but the electric fuel pump sounded much louder than usual, so he shut the engine down. On the third engine start, the electric fuel pump remained louder than normal, and he noticed that the fuel pressure was fluctuating. The fuel pressure recovered to 3.5 pounds per square inch (psi), and he completed a normal engine run-up. Shortly thereafter, the pilot departed. As the airplane reached about 50 to 100 ft above ground level, the engine surged, and he noticed that the fuel pressure had decreased to 1.0 psi. He retarded the throttle to land. The airplane touched down hard and sustained substantial damage to the fuselage. After the accident, the engine was started and run for several minutes multiple times with no anomalies noted. Testing of the electric fuel pump revealed that it made a loud noise when air passed through it; therefore, the noise heard by the pilot during the engine starts was likely due to air in the fuel system. The accident airplane did not have a fuel bypass around the electric fuel pump, which the engine manufacture’s installation instructions warn is a necessary safeguard. Examination of onboard engine monitoring data revealed that during the climb, the fuel pressure suddenly decreased to 1.1 psi, and the fuel flow simultaneously reached 9.8 gallons per hour. The fuel flow continued to oscillate indicating that the fuel flow to the engine was experiencing intermittent interruptions consistent with fuel vaporizing in the fuel lines (vapor lock).
HISTORY OF FLIGHT On April 22, 2020, about 1110 mountain daylight time, a Czech Sport Aircraft SportCruiser, N802PS, was substantially damaged when it was involved in an accident at Logan-Cache Airport, Logan, Utah. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The student pilot stated that he was making his second solo cross-country flight. He departed from South Valley Regional Airport, Salt Lake City, Utah about 0900 and completed two practice touch-and-go takeoffs and landings in Ogden, Utah. Thereafter, the pilot continued to Logan where he completed a full stop landing and shut down the engine. After a short time, he started the engine, and during the run-up procedure, he performed a magneto check at which time the engine momentarily experienced a total loss of power. The pilot shut down the engine and spoke with his instructor on his cell phone. He then started the engine again but thought that the electric fuel pump sounded much louder than usual, so he shut the engine down. On the third engine start, the electric fuel pump remained louder than normal, and he noticed that the fuel pressure was fluctuating within the normal range but would temporarily drop to 1.8 pounds per square inch (psi) when he turned on the avionics. The fuel pressure recovered to 3.5 psi, and he completed a normal engine runup. The pilot further stated that he taxied to runway 28 and proceeded to depart. As the airplane reached about 50 to 100 ft above ground level, the engine surged, and he noticed that the fuel pressure had decreased to 1.0 psi. He retarded the throttle and landed straight ahead as he thought there was enough runway remaining. The airplane touched down hard and sustained substantial damage to the fuselage. WRECKAGE AND IMPACT INFORMATION Engine Monitor Data The airplane was equipped with a Dynon Avionics Flight DEK-D120 combination electronic flight instrument system (EFIS) and engine monitoring system (EMS). The unit was installed on the left side of the instrument panel directly in front of the pilot. The unit could store over 180 engine and flight parameters in non-volatile memory. Data from the unit was downloaded. The time stamps between recorded hits occurred about every 5 seconds, and the data contained the last several flights. Several of the parameters were obviously erroneous and could not be used to obtain any meaningful information. Examination of the data revealed that the accident flight started with both fuel tanks having about 9.4 gallons apiece. On the accident flight, the engine rpm speed gradually increased, and when reaching 4,954 rpm, the fuel pressure suddenly decreased to 1.9 psi and then to 1.1 psi as the fuel flow reached 9.8 gallons per hour (gph). The rpm then gradually began to decrease, and the fuel flow oscillated between 0.9 and 4.6 psi. In the recorded points just before the accident, the fuel flow was below 2.2 psi, and the oil temperature had risen to 180° F. Wreckage Examination Following recovery, a mechanic disconnected the fuel lines from each carburetor and activated the electric fuel pump. The fuel flow appeared normal, and there was no debris found in the fuel. A postaccident examination by a National Transportation Safety Board investigator revealed that there was no impact damage to the exterior of the engine. A fuel source was plumbed to the engine, and investigators ran the engine. The engine was started and run for several minutes multiple times with no anomalies noted. The fuel system was examined after it had been flow tested by the mechanic. The examination revealed that the fuel return line was plumbed to the right wing, and the fuel line from the fuel pump drain was routed to the slipstream. The Facet Automotive Cube electric fuel pump was plumbed in parallel with the BDC Corona engine-driven pump; there was no check valve in the system. When the electric fuel pump was activated, a loud noise was heard coming from the pump body. Once the pump was primed with fuel, the noise stopped, and fuel pressure went from 1.0 to 3.5 psi for about 1 minute and then fluctuated between 1.6 to1.7 psi. The Rotax Installation Manual (IM) specified that the electric fuel pump should be in series with and before the engine-driven pump. The IM stated that the electric pump was required "in case of a malfunction or defect" of the engine-drive pump and was also required to preclude vapor lock of the fuel supply to the engine-driven pump. The IM installation diagram depicted a fuel bypass circuit around the electric pump, but the accident airplane was not plumbed in accordance with this diagram. Section 14.2 of the Rotax IM cited the minimum, normal, and maximum fuel pressure limits as 2.2, 4.4, and 5.8 psi, respectively, and stated that the pressures were to be measured at the fuel manifold. The IM contained the warning that fuel pressure in excess of the stated limit can lead to an override of the float valve and "subsequent engine stop." The Rotax IM defined a "Warning" as "an instruction which, if not followed, may cause serious injury, including the possibility of death." The IM also noted that "if an electrical auxiliary pump is installed, the whole fuel system has to be designed to warrant engine operation within the specified pressure limits." Finally, the IM contained the caution that "the fuel pressure of an additional auxiliary fuel pump should not exceed...4.4 psi." The airplane was equipped with a fuel flow transducer that incorporated an internal rotor mounted within a chamber. As fuel passed through the chamber, the rotor spun, interrupting an opto-electronic pickup, which created a pulsed electrical signal that had a period proportional to the fuel flow rate. According to a technical representative from Rotax, the introduction of air into the fuel supply lines can result in higher-than-normal readings of fuel flow (over 8 to 9 gph). When air inadvertently enters a rotor style flow transducer through the fuel lines, the rotor is free to spin at the velocity of the air that passes over it. This velocity is higher for air than it is for fuel, and as such, "vapor lock" is often represented as spikes in fuel flow. Additionally, with air in the system, pulses of air from the fuel pump can cause the rotor to spin back and forth in both directions. Under these conditions, the pickup still measures flow irrespective of direction, resulting in "jumping" fuel flow readings. ADDITIONAL INFORMATION The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) defines vapor lock as; A problem that mostly affects gasoline-fueled internal combustion engines. It occurs when liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporize due to being heated by the engine, by the local climate, or due to a lower boiling point at high altitude.
A partial loss of engine power during takeoff due to vapor lock.
Source: NTSB Aviation Accident Database
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