NTSB Factual Report

On December 23, 2015, about 1520 central standard time, a Beech model V35B single-engine airplane, N4523A, was substantially damaged during a wheels-up forced landing at Tahlequah Municipal Airport (TQH), Tahlequah, Oklahoma. The private pilot was not injured. The airplane was registered to and operated by Beech V-35 LLC, under the provisions of 14 Code of Federal Regulations Part 91 without a flight plan. Day visual meteorological conditions prevailed at the time of the accident. The business flight departed TQH at 1515 and had the intended destination of William R Pogue Municipal Airport (OWP), Sand Springs, Oklahoma.

The pilot reported that, before the accident flight, he topped-off the left fuel tank and estimated that the right fuel tank contained 15-20 gallons. He stated that after a normal takeoff from runway 35 he turned to a 283 degree heading toward the intended destination and continued to climb to his planned cruise altitude of 4,500 feet mean sea level (msl). He remarked that he used 25-inches of engine manifold pressure and 2,500 rpm during the cruise climb.

The pilot reported that, about 2.5 miles from the departure airport, as the airplane climbed through 2,500 feet msl, the airplane experienced a significant loss of engine power. He remarked that he did not hear a corresponding decrease in engine noise; however, he acknowledged that he was wearing a noise-canceling headset. The pilot stated that he made an immediate turn back to the airport for a forced landing on runway 17. During the turn back toward the airport, the engine regained power for a short period of 1-2 seconds. The pilot was initially concerned that the airplane might not have enough altitude to reach the runway and, as such, he decided to keep the landing gear and flaps retracted. Additionally, the pilot indicated that he pulled the propeller control full aft in attempt to further reduce the propeller drag. He reported that the propeller continued to rotate/windmill throughout the forced landing. The pilot admitted that he became distracted with the forced landing and forgot to extend the landing gear once the airplane was in a position to safely to land on the runway. As such, the airplane sustained substantial damage to the lower fuselage, including several structural bulkheads, when it landed wheels-up on the runway.

The pilot stated that, following the force landing, an individual approached him and remarked that he had heard the airplane approach the airport before the wheels-up landing. This individual remarked that airplane sounded like it was experiencing a propeller over-speed condition or governor failure.

The pilot further reported that, before the accident flight, the propeller speed did not decrease significantly when he cycled the propeller control during his before-takeoff procedures. Additionally, he indicated that earlier the same day, before the previous flight leg from Seminole Municipal Airport (SRE) to TQH, he also did not observe an appreciable drop in propeller speed as he attempted to cycle the propeller during his before-takeoff procedures.

Following the accident, a local aviation mechanic hoisted the airplane and extended the landing gear using the manual extension procedure. After a successful manual extension, the landing gear was partially retracted before it was extended a second time using the electric motor. There were no anomalies identified with the landing gear extension/retraction system that would have precluded its normal operation during the accident flight. The airplane was subsequently recovered from the runway to a secured hangar.

An additional examination was completed by a Federal Aviation Administration (FAA) Airworthiness Inspector, a representative from Hartzell Propeller, and a local aviation mechanic. A review of the runway revealed there were 12 discernible propeller blade strike marks in the asphalt surface. The first propeller strike mark was located about 800 feet from the runway 17 threshold. The runway exhibited additional scrape marks, for about 500 feet, that were consistent with the lower airplane fuselage abrading against the asphalt surface during a wheels-up landing. A visual examination of the airplane revealed ground impact damage to the lower fuselage skins and several structural bulkheads. Additionally, the nose landing gear doors and exhaust pipes exhibited ground impact damage. The left fuel tank was full and the right tank was about 1/2 full. A fluid, blue in color, consistent with 100 low lead aviation fuel, was recovered from both fuel tanks. The fuel samples did not contain any water or particulate contamination.

The propeller remained attached to the engine and its spinner dome appeared undamaged. All three blade tips were bent aft with chordwise and spanwise scoring. All three blades were secure in the hub at the low pitch stop position and could not be rotated by hand. The cylinder was pressurized with shop air and all three blades cycled in pitch without anomaly. There was no oil was present on aft side of the piston, which established that there were no oil leaks past the piston rings. Additionally, the propeller blades cycled smoothly when the engine case oil passage was pressurized with shop air. There were no anomalies identified with the propeller that would have precluded its normal operation.

The propeller governor was removed and examined/tested at the manufacturer. The governor drive shaft turned freely by hand and oil was discharged from the unit in conjunction with the shaft being rotated. Radiographic imaging confirmed there were no anomalies with the governor assembly. Further, an acceptance bench test did not identify any discrepancies that would have precluded normal governor operation.

The engine remained attached to the firewall by its mounts. Mechanical continuity was confirmed from the cockpit controls to their respective engine components. Internal engine and valve train continuity were confirmed as the engine crankshaft was rotated. Compression and suction were noted on all cylinders in conjunction with crankshaft rotation. The upper spark plugs were removed and exhibited features consistent with normal engine operation. Both magnetos provided spark on all leads as the engine crankshaft was rotated. The engine-to-magneto timing, 22 degrees before top dead center, was consistent with the engine manufacturer's specification.

To facilitate an operational engine test, the propeller governor was reinstalled and the damaged three-blade propeller was replaced with a two-blade test propeller. The engine started after being primed, but then experienced a total loss of power after few seconds. The engine was restarted with the electric fuel boost pump on and it operated normally while the electric boost pump remained on; however, a significant fuel leak developed during the second test and the engine experienced a loss of power when the electric fuel boost pump was turned off. Further examination revealed a loose fuel line connection where the airframe fuel supply connected to the mechanical fuel pump inlet. After tightening the loose fuel line connection, the engine was started for a third time and operated normally with and without the electrical fuel boost pump turned on. The engine ran smoothly throughout its normal speed range and demonstrated the ability to develop 2,700 RPM.

On June 22, 2015, the accident engine, a Continental Motors model IO-550-B51, serial number 834702-R, was overhauled by D&B Aircraft Engines in Bethany, Oklahoma. On July 10, 2015, at 4,143 hours tachometer time, the overhauled engine was reinstalled on the accident airplane by Red Cloud Aviation, LLC, in Seminole, Oklahoma. According to the engine logbook, the mechanic noted no leaks after the reinstalled engine was test run. On September 29, 2015, 4 hours since the engine overhaul, the airplane was taken to D&B Aircraft Engines to resolve a low power engine shudder at 17-inch manifold pressure and excessive oil consumption concerns. According to the logbook entry, D&B Aircraft Engines reconditioned the intake drain insert and made unspecified engine adjustments. On November 12, 2015, 9 hours since the engine overhaul, the oil and oil filter were replaced. According to the logbook entry, no anomalies or leaks were noted during an engine ground run following the oil change. The airplane's recording tachometer read 4,153.8 at the accident site. The engine had accumulated 10.8 hours since the last overhaul.

NTSB Probable Cause

A partial loss of engine power shortly after takeoff due to an inadequately tightened fuel line. Also causal was the pilot's failure to extend the landing gear once the airplane was in a position to safely land on the runway.