Twentynine Palms, CA, USA
N2989P
CONSOLIDATED AERONAUTICS INC. LAKE LA-4-200
The pilot had recently purchased the airplane and was transporting it to his home airport. During the cross-country flight, the pilot stopped to refuel the airplane. During departure, the airplane climbed to an altitude of about 200 ft above ground level, at which point the engine lost partial power and was unable to maintain altitude. The pilot elected to perform an emergency off-airport landing, and the airplane touched down on desert terrain. During the landing, the airplane collided with a sign and nosed over, coming to rest inverted. The airplane had undergone a pre-buy and an annual inspection about 10 flight hours before the accident. The pilot stated that, on the day before the accident, he flight tested the airplane, during which time the manual turbocharger went into overboost for “a second” before he pulled the power back. A postaccident examination revealed that several ceramic cores of the spark plugs were cracked. The combustion chambers were free from deposits, consistent with a preignition or detonation event. It is unknown if the overboost event that the pilot described resulted in this damage. The magnetos, while still installed on the engine, did not produce a consistent spark, and their timing could not be determined. The magnetos were then removed from the engine. The right magneto was functionally tested and operated normally. The left magneto capacitor lead insulation had previously been cut, exposing the center conductor wire, consistent with improper assembly. The contact point tungsten faces were both corroded and exhibited an oxide crust on the external surfaces of the tungsten. A functional test, revealed the left magneto would not produce spark at different rpms. The left magneto was likely not operating during the accident takeoff, which, along with the cracked spark plugs, would have resulted in a partial loss of engine power.
History of Flight On April 21, 2021, about 1410 Pacific daylight time, a Consolidated Aeronautics Lake LA-4-200, N2989P, sustained substantial damage when it was involved in an accident near Twentynine Palms, California. The pilot, the sole occupant, sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that he had recently purchased the airplane and had undergone training in the airplane make and model. The purpose of the flight was for the pilot to transport the airplane from the seller’s location in Novato, California, to his home airport in Texas. On the morning of the accident, the pilot departed about 0800, made a fuel stop, and departed again before landing in Twentynine Palms about 1330. He filled the fuel tanks to their maximum capacity and began the departure from runway 26. The airplane climbed to about 200 ft above ground level (agl), at which point the engine lost partial power and was unable to maintain altitude. The engine began to vibrate, and the pilot could hear a “loud chatter noise” from the engine area. He noted that the manifold pressure gauge appeared normal and that the digital tachometer displayed fluctuating rpm. The pilot verified that the auxiliary boost pump was selected to the “on” position and retracted the flaps to maximize the time that the airplane would be able to stay airborne. The pilot further stated that he was unable to maintain altitude and that, after determining that the airplane would not be able to return to the departure airport, he elected to make an emergency landing on a road. As the airplane approached the road, the pilot observed power lines and decided to have the airplane touch down on the adjacent desert terrain. During the landing, the airplane collided with a sign, and the airplane nosed over, coming to rest inverted. Aircraft Information The Lake LA-4-200 is a mid-wing single-engine amphibian airplane powered by a fuel-injected four-cylinder piston engine. The engine, which is mounted on a vertical pylon above the fuselage, drives the two-bladed constant-speed pusher propeller. In 1983, the accident airplane was outfitted with a Rayjay turbocharger under a supplemental type certificate. The pilot stated that, during the day before the accident, he flight tested the airplane, and the manual turbocharger went into overboost for “a second” before he pulled the power back. The airplane’s logbooks indicated that the engine was the original engine installed at the time of manufacture. The last annual inspection, which was also a pre-buy inspection, occurred on March 1, 2021, at a total time of 1,727 hours and about 10 hours before the accident. Records indicated that the last 500-hour magneto inspection was in May 2002 at a total aircraft time of 1,339 hours; the capacitor on the right magneto was replaced at a total time of 1,493 hours. Wreckage and Impact Information A postaccident examination of the engine found that the crankshaft could be rotated by hand using the propeller. The crankshaft was easy to rotate in both directions. A “thumb” compression test was performed on all cylinders and strong pressure was felt trying to escape at the upper spark plug bores. The entire valve train operated properly. Mechanical continuity was established throughout the rotating group, valve train, and accessory section during hand rotation of the crankshaft. Clean, uncontaminated oil was observed at all four rocker box areas. Removal of the spark plugs revealed that they were oily and that several had cracked ceramic cores. The cylinders were removed, and the pistons were free from deposits. The magnetos did not produce a consistent spark; as a result, their timing could not be determined. The magnetos were then tested at Kelly Aero in Montgomery, Alabama. Both magnetos were in good condition with no oil or dust contamination beyond normal wear. The distributor gears of both magnetos were free from damage. The right magneto was functionally tested, and it operated within test parameters, producing consistent spark at different rpm. The left magneto failed to produce a spark at different rpm; the impulse coupling engaged between 75 and150 rpm and then disengaged above 450 rpm. Disassembly of the left magneto revealed that capacitor lead insulation had previously been cut, which exposed the center conductor wire. The contact point tungsten faces were corroded and exhibited an oxide crust on the external surfaces of the tungsten (see the figure below). When the operational capacitor of the right magneto was replaced with the left magneto’s capacitor, consistent spark was produced at different rpm. Additionally, after replacing the corroded contact points of the left magneto with those from the right magneto, the left magneto also produced consistent spark at different rpm. Figure 1. Magneto points. Additional Information Lycoming Engines issued Mandatory Service Bulletin (SB) 592 regarding the corrective actions to be taken after an overboost event. For engines configured similarly to the accident engine, the SB states, in pertinent part, to inspect spark plugs for a ceramic core nose with a cracked or crazed surface. It is unknown if the overboost event that the pilot described made the accident airplane engine subject to the actions in the SB (because no information was available regarding the pressure exceedance and exact duration of the event).
A partial loss of engine power due to inadequate ignition from cracked spark plugs and a failed magneto.
Source: NTSB Aviation Accident Database
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