N733ZN

On September 20, 2023, about 0830 Pacific daylight time, a Cessna 172N, N733ZN, was substantially damaged when it was involved in an accident near Compton, California. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 flight.

The airplane had not been flown for about 2 months and because of this, the pilot planned to perform what he referred to as a “return to service test flight” flight for the owner, departing from Compton/Woodley Airport (CPM). He performed a preflight inspection and visually checked fuel quantity through the filler cap openings, cross-checked the quantity with the fuel gauges, and observed between 7 and 10 gallons per side. He checked the wing tank fuel drains for water and found none.

The left main and nose gear tires were low, so the pilot taxied the airplane to the fuel island to service them with air. Because the airplane had been sitting outside unused, he planned to perform a long engine run-up and a series of high-speed taxi runs and takeoff rolls. The run-up lasted between 15 to 20 minutes, during which he noticed that the engine was running rough on the right magneto. He pushed the throttle to the full forward position and leaned the mixture to resolve the issue; after another engine run-up, the roughness had resolved.

He then began the high-speed takeoff runs and, with normal indications, he decided to continue with a flight on the third attempt. After reaching about 50 to 100 ft above ground level, the engine momentarily lost power, followed a short time later by a complete loss of power. He performed a forced landing directly ahead which resulted in substantial damage to the left wing and forward fuselage after striking a parked vehicle.

Figure 1 – Airplane on its nose at the accident site (photo courtesy of LA County Sheriff)

An annual inspection was completed on July 15, 2023. The following day 20 gallons of fuel was added, and the airplane was returned to service. At the time of the accident, the airplane had accrued an additional 1.7 hours of flight. Before the most recent annual, the last maintenance event occurred in November 2019 and was again for an annual inspection. During those intervening 4 years the airplane accrued 2 hours of flight.

The left fuel tank was breached during the accident and was observed by first response personal to be leaking fuel. A sheriff’s deputy checked the fuel quantity through the filler neck in the right tank and observed fuel at a depth of 3 inches. The nose gear assembly used a standard air/oil strut, which had folded aft and detached during the accident, so the airplane was in a nose-down attitude when the fuel level was checked.

Postaccident examination revealed that the airplane exhibited evidence of long-term non-use, such as corrosion within the engine compartment and many airframe skin surfaces (see Figure 4), along with mold-like deposits on cabin upholstery and plastic facias.

A complete examination of the fuel system revealed that the fuel strainer was full of fluid, which appeared to be about ¼ blue-colored fuel, and ¾ water (see Figure 2). The carburetor bowl was drained and contained 75 ml of fuel and 25 ml of water (see Figure 3). Additionally, about 10 ml of water was found in the right fuel tank. Internal fuel tank inspection showed globules of water were still present inside the right tank. The lower surfaces of both tanks exhibited corrosion-like discoloration at their respective roots and forward towards the wing leading edge. Removal of both the left and right tank fuel drains, which were located at the rear of each tank, revealed about ¼ inch corrosion to their lower surfaces.

Accident damage prevented an assessment of the condition of the nose gear strut assembly to confirm if it had been adequately serviced.

Figure 2 – Fuel and water in strainer

Figure 3 - Fuel and water in carburetor

The right and left fuel cap rubber gaskets were degraded, brittle and cracked, and neither was providing a firm seal against the tank filler neck. The left tank gasket was completely severed by a crack that breached its entire radius (see Figure 4).

Figure 4 – Cracked left fuel tank cap gasket and tank skin corrosion

Cessna Single Engine Service Bulletin SEB 92-26 revision 1 provided a modification for installing additional fuel drains in the wing fuel tanks. The modification was designed to assist in the detection and removal of water or other contaminants in the tanks. Although Cessna stated that compliance was mandatory, FAA regulations do not require adherence to service bulletins for Part 91 operations, and the bulletin had not been applied to the accident airplane.

The airplane was stored outside and rain showers had passed through the area during the two-week period leading up to the accident.