N37MB

On November 17, 2023, about 1708 eastern standard time, an experimental amateur-built Lancair IV-P, N37MB, was substantially damaged when it was involved in an accident near Perry, Florida. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

According to the pilot, he was in cruise flight at 11,500 ft msl with about 40 minutes of daylight remaining when he noted that a ceiling had developed below him. Accordingly, he decided to descend through a hole in the cloud layer and divert to Perry-Foley Airport (FPY), Perry, Florida. When the airplane levelled off under the cloud layer at 2,000 ft msl, he pushed in the throttle but “nothing happened.” The propeller was windmilling, and he thought the fuel-injected engine was at idle power. After several seconds, he pulled the throttle fully out expecting the engine to slow, but the engine power remained unchanged at the low-power setting. Realizing he had lost engine power, the pilot switched fuel tanks and enrichened the mixture; however, he was unable to restore power to the engine. He chose to execute a forced landing and considered landing on a road but believed that he could not slow the airplane enough to make a safe landing, so he landed straight ahead into sapling pine trees. The airplane nosed over and sustained substantial damage to the wings and fuselage; the pilot exited the airplane unassisted.

Postaccident examination of the airframe and engine revealed that the fuel strainer contained fuel with a color and odor consistent with 100LL Avgas. There were no signs of debris or water contamination in the retrieved fuel sample. The fuel strainer bowl was removed, and the fuel strainer screen was clear of any contamination. The throttle, mixture, and propeller controls were secured in the cockpit and at their respective control arms at the engine. The crankshaft was rotated by hand and continuity was established between the crankshaft, camshaft, connecting rods, and associated components. All six cylinders displayed good thumb compression and suction. Examination of the engine and airframe fuel system revealed no anomalies; therefore, a determination was made to ship the engine to the manufacturer for an engine test run.

At the manufacturer’s facility, the engine was prepared to run in the test cell. The oil sump was impact damaged and was replaced for testing. A fracture was observed on the No. 2 turbocharger exhaust where it had been previously welded. No determination could be made as to whether this was impact-related damage. The magneto-to-engine timing was confirmed to be within specification. A replacement propeller was installed on the engine. The engine started without hesitation in the test cell and ran at idle for 5 minutes, followed by subsequent 5-minute runs at each of the following rpm settings: 1200,1600, 2100, 2450, and then again at idle. Although the engine ran normally at all rpm settings, the engine test run revealed that the fuel system was set too lean, and the manifold pressure was about 2 inches of mercury lower than that required to produce rated power.

Following these static engine runs, the engine was brought to idle and then the throttle was rapidly advanced. This sequence was repeated several times, and when the throttle was advanced quickly, the engine ran very rich with black exhaust smoke, and then would falter. If the throttle was not immediately retarded, the engine lost power completely. If the engine was immediately brought back to idle after it faltered upon rapid throttle advancement, the engine regained power.