History of Flight
On April 21, 2021, about 1410 Pacific daylight time, a Consolidated Aeronautics Lake LA-4-200, registration N2989P, sustained substantial damage during an accident near Twentynine Palms, California. The pilot, the sole occupant, sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
The pilot, who had recently purchased the airplane and received training in the make and model, intended to transport it from Novato, California, to his home airport in Texas. He departed about 0800, made a fuel stop, and arrived at Twentynine Palms about 1330. After filling the fuel tanks to capacity, he departed from runway 26. The airplane climbed to about 200 ft above ground level when the engine lost partial power and could not maintain altitude. The engine began to vibrate, and the pilot heard a loud chatter noise from the engine area. The manifold pressure gauge appeared normal, but the digital tachometer displayed fluctuating rpm. The pilot turned on the auxiliary boost pump and retracted the flaps to maximize airborne time.
Unable to maintain altitude and determining that the airplane could not return to the airport, the pilot elected to make an emergency landing on a road. As he approached the road, he observed power lines and decided to land on adjacent desert terrain. During the landing, the airplane collided with a sign, nosed over, and came to rest inverted.
Aircraft Information
The Lake LA-4-200 is a mid-wing single-engine amphibian powered by a fuel-injected four-cylinder piston engine mounted on a vertical pylon above the fuselage, driving a two-bladed constant-speed pusher propeller. In 1983, the accident airplane was equipped with a Rayjay turbocharger under a supplemental type certificate. The pilot reported that during a flight test the day before the accident, the manual turbocharger briefly went into overboost before he reduced power.
The airplane’s logbooks indicated the engine was original. The last annual and pre-buy inspection occurred on March 1, 2021, at a total time of 1,727 hours, about 10 hours before the accident. The last 500-hour magneto inspection was in May 2002 at 1,339 hours; the right magneto capacitor was replaced at 1,493 hours.
Wreckage and Impact Information
Postaccident examination of the engine found that the crankshaft could be rotated by hand via the propeller, easily in both directions. A thumb compression test on all cylinders showed strong pressure escaping at the upper spark plug bores. The valve train operated properly, and mechanical continuity was established throughout the rotating group, valve train, and accessory section. Clean, uncontaminated oil was present at all four rocker box areas.
The spark plugs were oily, and several had cracked ceramic cores. Cylinders were removed, and pistons were free from deposits.
The magnetos did not produce consistent spark, so timing could not be determined. They were tested at Kelly Aero in Montgomery, Alabama. Both magnetos were in good condition with no contamination beyond normal wear. The right magneto operated within test parameters, producing consistent spark at various rpm. The left magneto failed to produce spark at different rpm; its impulse coupling engaged between 75 and 150 rpm and disengaged above 450 rpm.
Disassembly of the left magneto revealed that the capacitor lead insulation had been cut, exposing the center conductor. The contact point tungsten faces were corroded with an oxide crust. When the left magneto’s capacitor was replaced with the right magneto’s operational capacitor, consistent spark was produced. Similarly, after replacing the left magneto’s corroded contact points with those from the right magneto, consistent spark was achieved.
Additional Information
Lycoming Engines issued Mandatory Service Bulletin 592 regarding corrective actions after an overboost event. For engines like the accident engine, the SB specifies inspecting spark plugs for cracked or crazed ceramic core noses. It is unknown whether the overboost event described by the pilot made the engine subject to the SB actions, as no information was available on the pressure exceedance and exact duration.