Santa Monica, CA, USA
N1111X
CZECH AIRCRAFT WORKS SPOL SRO SPORTCRUISER
The student pilot had just completed two uneventful takeoffs and landings in the light-sport airplane. As he approached the runway's hold-short line to wait for the third takeoff clearance, a pilot from another aircraft in the traffic pattern declared an emergency. The student remained in the airplane with the engine running for about 20 minutes before receiving a takeoff clearance. Data from the airplane's engine monitor indicated that, while the airplane was waiting, multiple engine temperature limits were exceeded, and the fuel flow became erratic. The student did not notice the exceedances, and shortly after takeoff, the engine lost partial power, and the airplane began to descend. The student then initiated a 180° turn back toward the airport. The airplane landed long, and the student was unable to slow the airplane before it departed the elevated section of the runway and fell 10 ft. The airplane sustained substantial damage to the firewall and lower fuselage structure. The engine monitor data revealed that, during the first two previous takeoffs and landings, the fuel flow indications were normal. However, as stated previously, after the airplane had been holding short for about 20 minutes awaiting clearance for the next takeoff, multiple engine temperature limits were exceeded, and the fuel flow indications began to oscillate. Once the takeoff began, the fuel flow continued to oscillate, indicating that the fuel flow to the engine was experiencing intermittent interruptions, which was consistent with the fuel system experiencing vapor in the fuel lines (vapor lock). The vapor lock was likely caused by the engine bay becoming hot during the extended ground hold after the airplane had previously being flown for two flights, which resulted in heat-soaking of the fuel system. About 4 years before the accident, the engine manufacturer amended its engine installation manual to recommend the installation of a fuel return line, which was designed to prevent engine malfunctions caused by the formation of vapor in the fuel system. Examination of the airplane's fuel system revealed that a fuel return line had not been installed. The airplane manufacturer did not mandate the installation of a fuel return line until about 17 months after the accident, at which time, it issued a safety alert mandating the installation of the fuel line in accordance with the updated engine installation manual. Ten months later, the airplane manufacturer issued another alert, recommending updates to the Pilot's Operating Handbook by adding a warning that contained procedures to follow to limit the possibility of vapor lock. However, although the lack of a fuel return line could have contributed to the development of vapor lock, it more likely occurred because the student allowed the engine to overheat during the ground hold.
HISTORY OF FLIGHTOn May 22, 2016, at 1332 Pacific daylight time, a Czech Aircraft Works SPOL SRO, SportCruiser, N1111X, departed the runway after a loss of engine power during the initial climb from Santa Monica Municipal Airport (SMO), Santa Monica, California. The student pilot was not injured, and the airplane sustained substantial damage. The light-sport airplane was registered to and operated by Santa Monica Flyers, Inc., under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The local flight departed SMO at 1330. The student pilot had just completed two uneventful takeoffs and landings while remaining within the traffic pattern. As he approached the hold short line for runway 21 in preparation for his third takeoff, an airplane in the traffic pattern declared an emergency, and tower controllers temporarily suspended all takeoffs. The pilot remained in the airplane with the engine still running at idle. He stated that while waiting, the airplane was on a heading of about 350°, and he monitored the engine's cylinder head temperatures and intermittently increased engine speed in an attempt to keep the engine cool. After holding short for 20 minutes the pilot was given a takeoff clearance. The takeoff roll and initial climb were uneventful, however, once the airplane reached an altitude of about 500 ft above ground level (agl), the engine began to lose power, and the airplane began descending. The pilot stated that he did not have sufficient altitude to perform trouble shooting steps, and immediately initiated a 180o right turn in an effort to land back on runway 3. The airplane became realigned with the runway centerline about midfield, and after touchdown the pilot applied full brake pressure, but was unable to slow the airplane down sufficiently. The airplane passed through the northeast run-up area and taxiway, and departed the elevated section of the runway, dropping down onto the airport perimeter road 10 ft below. Both the nose and main landing gear struck the curb, and the airplane came to rest on a grassy knoll within the airport perimeter, about 180 ft beyond the threshold of runway 21. The airplane sustained substantial damage to the firewall and lower fuselage structure during the accident sequence, and both wings, along with their integral fuel tanks, were intact and undamaged. AIRCRAFT INFORMATIONThe airplane was manufactured in 2008, and equipped with a 4-cylinder, liquid-/air-cooled, Rotax 912-ULS engine. AIRPORT INFORMATIONThe airplane was manufactured in 2008, and equipped with a 4-cylinder, liquid-/air-cooled, Rotax 912-ULS engine. WRECKAGE AND IMPACT INFORMATIONPost-accident examination at the accident site by the NTSB investigator-in-charge (IIC) revealed that the left- and right-wing fuel tanks both contained fuel, along with both carburetor bowls. A follow up examination was performed; there was no evidence of oil or coolant loss, and no anomalies with the airframe or engine were found which would have precluded normal operation. The engine was then removed and transported to the facilities of Rotech Flight Safety (Rotax Aircraft Engines) for further examination and an engine test run. No anomalies were noted, and the engine performed nominally at all speeds in an engine test cell. A complete examination report is contained in the public docket. Engine Monitor The airplane was equipped with a Dynon EMS-D120 engine monitoring system, mounted on the right side of the instrument panel, which was configured to record engine parameters including oil pressure and temperature, fuel pressure and flow, manifold pressure, engine speed, and the cylinder and exhaust gas temperatures (CHT, EGT) for cylinders one and two. The unit also recorded the airplane's GPS position and ground speed. Examination of the data revealed that for both prior takeoffs and landings, the fuel flow remained at about 1 gallon per hour (gph) during the ground idle phase, and climbed to about 6.5 gph during the takeoff and initial climb. Oil temperatures remained at about 175° F throughout, and cylinder head temperatures averaged about 175° F on the ground, and 230° F during takeoff. Engine speed during takeoff was about 5,100 rpm, and manifold pressure dropped from 29.1 to 27.8 inches of mercury as the climb progressed. For the first ten minutes while the airplane was holding short and waiting for the takeoff clearance of the accident flight, the CHT's began to climb, with cylinder 2 reaching an average of about 330° F. During that period, the oil temperature climbed to 222° F while the oil pressure began to drop from about 46 to 30 lbs per square inch (psi). Fuel flow and pressure remained constant at about 1 gph and 5 psi respectively. During the next 10 minutes, the oil temperature continued to rise with an accompanying drop in oil pressure, while the fuel flow began to oscillate, varying between 0 and 3 gph. About two minutes before takeoff, the oil temperature reached its highest average level of 270° F, with intermittent readings reaching as high as 337° F, while the oil pressure had dropped to 22 psi. The takeoff then began, but the fuel flow, rather than reaching 6.5 gph as before, began to oscillate between 5.4 and 9.1 gph. The engine speed reached 4,800 rpm for about 30 seconds, and then dropped to about 4,300 rpm; the manifold pressure remained steady at 30.03 inches of mercury throughout the takeoff and initial climb, until the data ended. During the ten minutes while the airplane was holding short just before takeoff, two distinct increases in engine speed of about 400 rpm were observed, lasting 30 and 60 seconds respectively. These changes appeared consistent with the pilot's attempt to keep the engine cool. The speed changes did not make any appreciable difference to the average engine temperatures. ADDITIONAL INFORMATIONThe engines temperature operating limitations, documented in both the flight manual and on the EMS-D120 gauges (through green, yellow, and red display bands), indicated the following: Normal operating range for oil temperature was between 194 and 230 °F, with a caution range of 230 to 266 °F and a maximum (red-line) limit of 266 °F. The normal cylinder head temperature operating range was between 167 and 230 °F, the caution range was 230 to 275 °F, and the maximum limit was 275 °F. The EMS-D120 was capable of displaying discrete alerts in the event of engine temperature exceedances, however the alert feature had not been enabled. The SportCruiser pilot operating handbook (POH) warned that takeoff is prohibited if engine instrument values are above operational limits. Fuel Flow Sensors The airplane was equipped with a FloScan 200 series fuel flow transducer. The unit's design 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 - the period of which was proportional to the fuel flow rate. According to technical representatives from FloScan, the introduction of air into the fuel supply lines can cause the unit to read higher than normal fuel flow rates. According to technical representatives from Electronics International Inc. (EI) (who manufacture the FT-60 fuel flow transducer, installed on later models of the SportCruiser), 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. Fuel and Fuel Testing Although the engine was capable of operating on 100 low-lead aviation gasoline, Rotax Engines recommended the use of automotive gasoline, because the lead in aviation fuel can cause stress on the valve seats, as well as create excessive lead deposits within the combustion chamber. The SportCruiser POH made similar recommendations, with the caveat that aviation gasoline should only be used, "in case of problems with vapor lock or when other types of gasoline are unavailable". Both Rotax Engines and Czech Aircraft Works recommended using automotive gasoline which meets the American Society for Testing and Materials (ASTM) standard D4814. The Rotax operating manual, and placards mounted throughout the airplane, indicated that fuel with a minimum research octane number (RON) of 95 and anti-knocking index (AKI) of 91 can be used. Rotax further stated in the engine operating manual, "Use only fuel suitable for the respective climatic zone", and "Risk of vapor formation if using winter fuel for summer operation". According to representatives from Santa Monica Flyers, their Rotax-equipped fleet was fueled with premium-grade automotive fuel purchased from a local automotive gasoline station, and then transported to the airport in a fuel truck. The last fill-up occurred the morning of the accident, and the accident airplane used fuel from that delivery. Fuel from the left wing fuel tank (the tank selected for the flight) was recovered from the airplane at the accident site, and analyzed at a petroleum testing laboratory. The results revealed that the fuel was the appropriate blend for the region and time of year, and had a RON value of 95.8. Fuel System An amendment to the Rotax 912-ULS installation manual was added on August 1, 2012. The amendment required the installation of a fuel return line, designed to prevent engine malfunctions caused by the formation of vapor in the fuel system. The amendment stated that compliance was mandatory. It further stated: "If the fuel distributor piece with regulator from Rotax is not available, the fuel pressure must be regulated by a restriction in the fuel return line, which ensures that the fuel pressure is under all operation condition within the operating limits specified by Rotax." Examination of the airplane's fuel system revealed that the fuel return line had not been installed. According to representatives from Czech Aircraft Works, the installation of a fuel return line was made standard on all SportCruiser airplanes manufactured after September 2010. A series of safety alerts were issued by Czech Aircraft Works during the two-year period following the accident, in response to limiting the possibility of vapor lock, specifically: Safety Alert SA-SC-006, issued on October 16, 2017 mandated the installation of a fuel return line in accordance with the updated recommendations in Chapter 73-00-00, of the Rotax installation manual. The alert was applicable to all SportCruiser airplanes manufactured before May 14, 2009 (The accident airplane was manufactured in 2008). Safety Alert SA-SC-011, issued on August 31, 2018, provided a set of updates to the POH regarding engine operation. One of the updates required the following addition to all sections of the POH that mentioned fuel: "WARNING Use only fuel formulated for the specific climate zone. Pay special attention to the current outside air temperature. Do not use winter MOGAS blends in warmer than normal temperatures. RISK OF VAPOR FORMATION IF WINTER FUEL IS USED FOR SUMMER OPERATION." 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. Contributing to the accident was the student pilot's failure to notice that the engine had exceeded multiple temperature limits and that the fuel flow had become erratic during an extended ground hold, which led to the vapor lock.
Source: NTSB Aviation Accident Database
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