N59MK

On March 12, 2024, about 1902 eastern standard time, a Beech K35, N59MK, was substantially damaged when it was involved in an accident near Front Royal, Virginia. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight.

The pilot departed on an aerial survey flight from Shannon Airport (EZF), Fredericksburg, Virginia, at 1301. The pilot reported that, during the flight, he attempted to adjust the propeller control with no response. The pilot slowed the airplane as he approached the survey area and the propeller became responsive, so he elected to continue with the survey. During the survey, he noted that the No. 3 cylinder exhaust gas temperature (EGT) value was low, which was abnormal. He continued the flight to see if the EGT would return to more normal indications, but it did not, and he chose to discontinue the survey and land at the destination airport. He began to climb the airplane and attempted to switch fuel tanks from the right main tank to the left main tank, but several minutes later, the engine began to stumble. He double-checked the fuel selector position and noted that it was on an auxiliary fuel tank, so he switched it to the left main fuel tank, and continued to climb to 6,300 ft. About 10 minutes later, the engine lost total power. He turned toward the nearest airport and attempted to restore power, but was unsuccessful. Realizing that the airplane would not reach the airport, the pilot performed a forced landing to a field, during which the airplane traveled through a tree line and the outboard portions of both wings separated from the airplane.

The pilot stated that he departed with the airplane fueled to its full capacity (99 gallons), and that the airplane was equipped with six fuel tanks. The pilot also commented that the engine was recently overhauled and had accrued fewer than 100 hours since the field overhaul was completed.

The airplane was equipped with two bladder-type main fuel tanks, one per wing, each with a capacity of 25 gallons, of which 3 gallons were unusable. It was also equipped with two bladder-type auxiliary fuel tanks, each with a 20-gallon capacity, of which 1 gallon was unusable. The airplane was also equipped with fiberglass wingtip fuel tanks.

While the wreckage was being recovered from the accident site, personnel from the recovery company removed about 5 gallons of fuel from the right wing fuel tanks and less than 1 gallon from the left wing fuel tanks. The wreckage was subsequently taken to an aircraft salvage facility for additional examination. The main and auxiliary fuel tanks did not display indications that they had been breached during the accident sequence. The wingtip tanks remained attached to the wings but were both ruptured. The main fuel tanks were cut adjacent to wing skin cuts made by recovery personnel to facilitate transportation. Portions of the wing fuel vent plumbing were also cut into sections adjacent to the recovery cuts made to the wings. The wing vent plumbing for each main and bladder tank was found to be free from blockage. The right wing siphon-break plumbing was partly obstructed by dirt near the wing port. The wingtip tank vent plumbing was free from obstructions.

The fuel supply lines from each auxiliary fuel tank to the fuel selector were cut adjacent to wing recovery cuts. The fuel supply plumbing was examined, and found to be free from obstructions, by passing air through both the main wing and auxiliary bladder tank plumbing, the fuel selector, and out the fuel strainer outlet. The wingtip tank plumbing was examined and found to be free from obstructions. The airplane’s battery was connected, and the auxiliary fuel pump operated normally. The fuel transfer pumps and solenoid valves were connected to a 12-volt battery and also operated normally. The fuel strainer and fuel strainer bowl were clean.

The propeller blades were cut midspan to facilitate a test run of the engine. Automotive gasoline was supplied at the fuel pump inlet from an external source. The fuel pump return was re-routed to the external source. The engine started and the throttle was advanced until the engine rpm reached 2,500. The airplane’s throttle, mixture, and propeller controls were operated with no discrepancies noted. The propeller lever controlled propeller rpm when inputs were applied. The engine test run was conducted for 5 minutes before concluding.

A test of the oil transfer collar was performed. Using a differential pressure gauge, 80 psi was applied to the governor oil pressure port. The oil pressure port maintained 42 psi when 80 psi was applied. The propeller governor remained attached to the front of the engine and was undamaged. Control continuity from the governor to the cockpit was established. The propeller governor was removed before the engine test run and the gasket screen was unobstructed. The propeller governor pumped oil when the drive was rotated by hand and was reinstalled to facilitate the engine test run. Following the test run, the propeller governor was sent for bench testing. There were no physical anomalies noted prior to testing and the governor was flushed prior to testing to mitigate any potential contamination from entering the test equipment. The unit was mounted to the test bench and run to reach the proper operating temperature. Once at temperature, the unit passed all of the requirements described per the original manufacturer’s manual requirements.

A J.P. Instruments EDM-900 was recovered from the airplane, and data were successfully downloaded from the unit following the engine test-run. Parameters from the accident flight, the postaccident engine test run, and a previous flight were recovered and evaluated. Review of the parameters from the accident flight showed that about 20 minutes prior to the end of the flight, the engine manifold pressure was about 22 inHg, while the engine fuel flow consistently indicated 15 gallons per hour (gph) with a fuel pressure of 15 psi. At 1847:20, the fuel pressure and fuel flow both simultaneously decreased to 0. As the fuel flow and pressure dropped, at 1847:30 the engine rpm increased from 2,600 to about 3,300 rpm before reducing to 2,000 rpm. Concurrently, all six CHTs and EGTs uniformly began to drop to 0. The engine’s manifold pressure also began increasing as the airplane descended.