N601SAZenith Aircraft ZODIAC 601 XL · 2019

On October 01, 2020, about 1500 Pacific daylight time, an experimental, amateur-built Zodiac 601XL, N601SA, was substantially damaged when it was involved in an accident in Burlington, Washington. The private pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.

The pilot reported that, before takeoff, he added fuel that contained a lead scavenging additive. He departed and remained in the airport traffic pattern. While turning from base to final about 300 ft above ground level (agl), the engine lost total power. He reported that he immediately retracted the flaps and engaged the starter in an unsuccessful attempt to restart the engine. The airplane impacted the ground about 1,500 ft short of the runway. As the airplane’s ground speed decreased, the airplane transitioned from the dirt surface to an asphalt surface road that ran perpendicular to the direction of travel. The airplane came to rest upright and sustained substantial damage to the lower fuselage longerons.

Federal Aviation Administration (FAA) aviation safety inspectors arrived at the accident site and interviewed the pilot. The pilot stated that when the engine lost power, the fuel selector was operating on the left wing fuel tank. Later, the pilot provided a written statement which indicated that at the fuel selector was on the right wing fuel tank at the time of the accident.

The night of the accident, the inspectors observed minimal fuel in the left wing tank, as the fuel level was about ½ inch from the fuel tank pickup. The right wing fuel tank contained considerably more fuel. Three weeks after the accident, during the FAA examination of the airplane’s fuel system, 5.5 gallons of fuel was drained from the right wing fuel tank, and about two gallons of fuel were drained from the left wing fuel tank. The pilot later stated that he drained fuel from the wing tanks before the examination took place. The amount of fuel onboard at the time of the accident could not be determined.

The fuel tanks were intact, and the fuel quantity indicators were accurate. Continuity of the fuel lines from the left and the right wing tanks was observed to the three-way fuel selector. The fuel selector valve was operational, and the fuel selector had three positions: Off, Left, and Right. The exterior of the gascolator was not damaged but exhibited a green film that saturated the fuel line from the gascolator to the engine-driven fuel pump. The fuel line from the gascolator to the carburetor was disconnected and purged. With the fuel selector in the Right position, no fuel could be extracted from the fuel line. With the fuel selector in the Left position, about one pint of a lime green-colored substance was purged from the fuel line. Examination of the throttle body also revealed the presence of the lime green substance.

NTSB Materials Laboratory Senior Chemist examined the lime green substance, which revealed an artificially high-octane level. The cause for the out-of-specification finding could not be determined. The results for the D86 Distillation were within the specified ranges for Avgas 100LL. The Fourier Transform Infrared (FTIR) spectrum and the distillation results indicate that the liquid was aviation gasoline and showed that the green-colored fuel should have been able to support combustion in an internal combustion engine.

According to an aviation gasoline manufacturer, for Avgas 100LL to turn green, “some contaminant that is broadly yellow through to red in colour” could be the cause for the color change. The presence of a fine ferrous particulate material or copper particulate material are examples of possible contaminants. Another possibility is fuel standing in the selector for a long period and the fuel itself degrading. According to the manufacturer, this would be unusual, but it could be possible if the selector has fuel wetted surfaces that are made of a catalytic metal such as copper.

The fuel manufacturer did not recommend the use of an additional lead scavenging additive since the fuel itself is formulated with additives specifically designed to reduce lead build-up on engine components.

Additional material testing could not be performed with the available fuel sample; therefore, the exact cause of the fuel color change could not be determined.

The airplane was released to the pilot, and he performed an examination of the airplane’s ignition system. The examination identified an instrument panel with an ignition switch A (Ignition A), and ignition switch B (Ignition B). In the airplane and affixed to the instrument panel, a placard identified Ignition A, and was additionally placarded with the word ‘Start’. About 1/2 inch to the right, was Ignition B along with an additional placard with the word ‘Run’. Ignition A was used to start the engine, while Ignition B was used for continuous engine operation, to run the engine. Examination of the ignition system was accomplished with the engine operating about 1,000 rpm. When Ignition A was independently operated in the ‘On’ position, operation was normal. When Ignition B was operated in the ‘On’ position, the system also presented as normal operation. However, with Ignition B ‘On’, when Ignition A was turned to the ‘Off’ position, the engine lost total power.

The pilot provided the results of his ignition system test and cited the coil selector as the cause of the ignition system failure. The pilot reported that Ignition A and Ignition B were connected by Mallory 29000 coil selector. The Mallory coil selector is a directional dual inlet, single outlet coil selector engineered for high performance enthusiasts or racing applications operating a dual ignition system. To isolate the Ignition B failure, the coil wires for Ignition A and Ignition B were interchanged. A successful engine start was accomplished with Ignition A in the ‘On’ position and remained operating with Ignition B in the ‘On’ position. Once again, when Ignition A was turned to the ‘Off’ position, the engine lost total power. Next, the wires identified as ‘R’ and ‘Y’ were disconnected and relocated to Coil A and wire ‘G’ was disconnected and interchanged with Coil B. The circuit breaker toggle switches installed to operated Ignition A and B, remained closed and did not trip during the test. However, the pilot’s test of the ignition system did not examine the distributor or the ignition control box.