N232LTCubcrafters CC11-160 · 2013

On January 16, 2015, about 1034 Pacific standard time, a Cubcrafters CC11-160 (Carbon Cub SS), N232LT, nosed over following a forced landing near San Luis Obispo, California. The experimental light-sport airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations Part 91. The commercial pilot and passenger were not injured, and the airplane sustained substantial damage to both wings during the accident sequence. The local sightseeing flight departed San Luis County Regional Airport, San Luis Obispo, at 0956. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot reported departing with the intention of performing a local sightseeing flight with a relative. The preflight checks were uneventful, and the engine contained 3.5 quarts of oil. About 40 minutes after takeoff he noticed the engine oil gauge was indicating "---" instead of oil pressure, and about 1 minute later, the engine started to, "skip." He made a radio call to the San Luis Obispo tower, declaring an emergency. A short time later the engine lost all power, and he guided it towards a highway. As he approached the highway he observed traffic, so configured the airplane for landing on an adjacent riverbed. During the landing roll the airplane nosed over, coming to rest inverted.

According to the U.S. Naval Observatory, Astronomical Applications Department, during the period of flight the altitude of the Sun when viewed from San Luis Obispo would have been about 26 degrees, with an Azimuth (E of N) of 147 degrees. This would have placed the suns position within the pilot's field of vision for the majority of the flight.

Weather at San Luis Obispo included clear skies, and visibilities of 10 miles.

On January 28, 2015, Cubcrafters issued Safety Alert SA 0010, which superseded Service Bulletin SB00025. The alert removed the inspection compliance requirements, and instead required replacement of the oil pressure line with the flexible hose. The alert required mandatory compliance, and was due within the next 10 flight hours, or at the next annual condition inspection, whichever occurred first.

FAA records indicated that in March 2013, the airplane was converted by Cubcrafters from the Special Light-Sport to Experimental Light-Sport category, and was issued a new set of operating limitations. According to a representative from Cubcrafters, the conversion is often requested by owners so that they can modify aircraft without the manufacturer's intervention.

The airplane was examined following recovery by the NTSB investigator-in-charge, along with representatives from the Federal Aviation Administration (FAA), Cubcrafters, and Danbury Aerospace. Examination revealed considerable oil streaking along the fuselage, covering the lower right side and entire belly. The oil residue was in an area that was obscured from the view of the pilot and passenger while in flight.

The engine oil level was checked, and the sump was empty. The engine was rotated by hand at the propeller, and excessive force was required to rotate the crankshaft. The engine cowling was removed, and the entire right side of the engine and firewall was coated in a film of oil. Further examination revealed that the oil pressure supply line, which connected the engine to the oil pressure transducer, had separated from its fitting on the engine accessory case.

The pressure line was made of copper tubing, and was connected to the transducer and accessory case with compression fittings, which utilized brass ferrules. The line exhibited necking at the separation surface adjacent to the ferrule edge. Removal of the line at the transducer revealed similar necking, but no separation.

Oil Pressure Line Service Bulletin

At the time of the accident, Cubcrafters Service Bulletin SB00025 Rev A, "Oil Pressure Line Inspection" was in effect. The purpose of the bulletin was to, "inspect the oil pressure line for leaks, and to provide the option to upgrade to a flexible hose."

The service bulletin called for mandatory compliance on or before the next 100-hour or annual condition inspection, with a subsequent recurrent inspection at 50-hour intervals, unless the line was upgraded to the flexible hose.

The last annual condition inspection occurred 130 flight hours prior to the accident. The mechanic who performed the inspection stated that he examined the oil lines in accordance with the Cubcrafters service manual. He was aware of Service Bulletin SB00025, (and had in fact ordered a set of flexible hoses for inventory) and although it was not specifically documented in the maintenance logbooks, he complied with it utilizing the inspection method both during the annual, and the two subsequent oil changes.

Engine Monitoring System

The airplane was equipped with a Dynon Avionics FlightDEK-D180 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 was capable of storing over 180 engine and flight parameters in non-volatile memory. Parameters included GPS location, engine oil pressure, and alert status.

Data for the flight was downloaded from the unit during the examination. The data indicated that shortly after takeoff the airplane initiated a climb to the southwest towards San Luis Obispo Bay. The engine oil pressure remained about 68 pounds per square inch (psi), and about 7 minutes later, having reached the bay, the airplane changed course to the east. Two minutes later the oil pressure reading dropped to -106 psi, and the unit logged an oil alert indicating the oil pressure was out of range. The flight continued for an additional 28 minutes on a meandering east-southeast track along the coast, and then inland to the accident location. Throughout the rest of the flight, the oil pressure remained at -106 psi, with the alert still active.

Documentation provided by Dynon indicated that the alert would have resulted in both the digital readout and oil pressure needle "tick" flashing. The airplane was not equipped with an audible alert system, or the optional external alert annunciator light.

In a subsequent exchange, the pilot stated that he noticed the oil pressure alert just before the loss of engine power occurred, conceding that it was possible that it came on earlier in the flight, and that he did not notice it.