NTSB Factual Report

On July 14, 2006, about 1500 Pacific daylight time, a Cessna 152, N25512, nosed over during an off airport forced landing near Pacoima, California. The student pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) sustained minor injuries; the student pilot was not injured. The airplane sustained substantial damage. The local instructional flight departed Whiteman Airport, Los Angeles, about 1459. Visual meteorological conditions prevailed, and no flight plan had been filed.

The CFI stated that engine roughness and a loss of power occurred about 100 feet above ground level (agl) while departing runway 12 following a touch-and-go. The CFI notified local air traffic control of his situation, and was cleared to land runway 30. Unable to reach the runway, the CFI elected to land in an area of spreading ponds about 3/4 mile southeast of Whiteman.

The student pilot/owner stated that he and the instructor flew the airplane 2 days before the accident. The engine had about 600 hours since new. A mechanic had recently replaced the left magneto, adjusted the valves, and replaced the alternator.

The student said that they departed on runway 14, and were past Osborne. They planned to do a touch-and-go, but the touchdown was a little long, so they made it a full stop landing. They taxied back, and took off again. About 150 feet above ground level (agl), the engine lost a little power (about 150 rpm). The airplane would not climb, but it could maintain altitude. They turned back toward the airport. During the turn the engine lost more power, and they could not maintain altitude. The CFI took control, and elected to land in a dry pond. The airplane touched down good, but the nose wheel dug into the soft dirt, and the airplane nosed over. The student thought that the CFI tried to put the flaps down, but doesn't think that they were full down. The engine was still running when they touched down.

The fire department turned off the master switch, ignition switch, the fuel selector valve, and ELT. There was no fuel leak; they pinched the fuel outlet.

The FAA and Textron Lycoming were parties to the investigation.

Investigators examined the wreckage at Aircraft Recovery Service, Littlerock, California, on July 17, 2006, under the supervision of the National Transportation Safety Board investigator-in-charge (IIC).

When the recovery agent picked the airplane up, it was inverted. He placed it inverted onto his trailer, and offloaded it at his yard in the same orientation with the damaged cowling still in place. Under the supervision of the IIC, the agent righted the airplane, and removed the cowling.

Investigators noted that none of the ignition leads were connected to the top spark plugs. Top plug number 3 was missing, and the cowling was oily in this area. The heli-coil thread insert of this spark plug bore was pulled out slightly near the terminating end of the heli-coil. All of the other top plugs were finger loose with about 1 1/2 threads engaged. The number 3 spark plug was not recovered.

All spark plugs were clean with no mechanical deformation. The spark plug electrodes were gray, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart.

A borescope inspection revealed no mechanical deformation on the valves, cylinder walls, or internal cylinder head.

Investigators manually rotated the crankshaft with the propeller. The crankshaft rotated freely, and the valves moved approximately the same amount of lift in firing order. The gears in the accessory case turned freely. Investigators obtained thumb compression on all cylinders in firing order.

Investigators manually rotated the magnetos, and both magnetos produced spark at all posts. They checked the magneto to engine timing utilizing a timing box (syncrophaser) device. The left magneto was at 20 degrees before top dead center (BTDC) on the number one cylinder, while the right was at 25 degrees BTDC. The engine data plate indicated 20 degrees spark advance.

An engine logbook entry dated July 10, 2006, noted that a mechanic adjusted the valve clearance, changed the oil and filter, and installed a new left magneto, new spark plugs, new muffler, new crankcase oil seal, new voltage regulator, and an overhauled alternator. The tachometer time was 616.8. The tachometer read 618.8 at the post accident examination.

NTSB Probable Cause

a loss of engine power due to the failure of maintenance personnel to tighten the top spark plugs, and install the leads for the ignition harness to the top spark plugs.