N512P

On January 14, 2023, about 1425 central standard time, a Pitts Model 12 airplane, N512P, sustained substantial damage when it was involved in an accident near Conroe, Texas. The pilot sustained minor injuries and the passenger sustained serious injuries. The airplane was operated as a Code of Federal Regulations Part 91 personal flight.

According to the pilot, he and the passenger were conducting a local flight to practice maneuvers and landings and the airplane contained about 40 gallons of fuel in the main fuel tank. About 3 to 4 minutes after takeoff, and at an altitude of 2,000 ft above ground level, the pilot noticed that a master warning light on the instrument panel illuminated but did not notice any anomalies or problems. The warning light then turned off, all indications were normal, and the engine was operating without issue. The pilot elected to return to the airport.

The pilot stated that, about 1 minute later, the engine sustained a series of power fluctuations; “like someone was turning the [magnetos] off and on.” When the pilot turned on the fuel boost pump, the engine produced a burst of power, and then lost power. The pilot switched from the main fuel tank to the auxiliary tank with no change noted to engine power, then switched back to the main fuel tank. Unable to reach the airport or a field due to a high descent rate, the pilot performed a forced landing to a nearby roadway. During the landing, the airplane impacted a powerline and terrain before coming to rest inverted. The airplane sustained substantial damage to the wings, fuselage, and empennage (see Figure 1).

Figure 1. Accident airplane as it came to rest (Source: Federal Aviation Administration)

The airplane is equipped with a main fuel tank in the forward fuselage and a wing tank in the upper wing with a total capacity of 54 gallons. An aluminum header or inverted tank with a pickup (flop) tube is located beneath the main tank and provides the fuel supply for inverted flight.

Postaccident examination of the airplane and engine revealed small particles of non-ferrous metal debris were noted throughout the airplane’s fuel system when fuel system components and fuel lines were removed. The airframe’s inverted fuel tank pickup tube was removed, and an o-ring at the end of the tube was not present. No evidence of the o-ring was noted in the fuel tank or fuel system. The engine was removed for a functional test in a test cell.

The engine fuel pump was removed, flushed, and functionally bench tested before the functional engine test due to the presence of metal debris in the fuel system. During the functional test, a leak was noted at the pump’s rear pressure relief valve and rear diaphragm. Although the leak was present, the fuel pump flows were normal at idle and cruise power settings. The fuel pump was reinstalled on the engine for the engine functional test. During the engine prime procedure, the engine fuel pump leaked from the rear pressure relief valve and diaphragm, as observed during the bench test. Due to the potential fire and safety concerns, the pump was removed and replaced with a slave pump. The accident fuel pump was disassembled; scratches and scoring marks were noted on the pressure relief valve seat, which allowed fuel into the air side cavity of the fuel pump (see Figure 2). The diaphragm was pliable and undamaged. Blue stains, consistent with aviation fuel, were noted on the external pump housing.

Figure 2. Engine fuel pump pressure relief valve with diaphragm

After the fuel pump was replaced, the engine started on the test cell without issue. Around 800 rpms, a vertical vibration was observed with the engine and test cell stand. The functional test was terminated at that time due to the abnormal vibrations.