History of Flight
On May 12, 2012, about 1245 eastern daylight time, a Beech A36TC, N2WZ, was substantially damaged when it impacted terrain during an attempted takeoff from Harnett Regional Jetport (HRJ), Erwin, North Carolina. The certificated private pilot and four passengers were not injured, and one passenger incurred minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which was destined for Darlington County Jetport (UDG), Darlington, South Carolina. The personal flight was conducted under 14 CFR Part 91.
According to the pilot, after an uneventful engine run-up, he initiated takeoff from runway 23. After liftoff and as the airplane accelerated beyond best angle of climb speed, the engine began "skipping and popping." The pilot felt a significant loss of power, but engine gauges showed no abnormalities. The airplane yawed left, descended, and impacted brush-covered terrain off the left side of the runway with the landing gear retracted.
A passenger reported that the takeoff appeared normal until after liftoff, when the engine "fluttered," the airplane lost airspeed, and drifted left of the runway before impact.
A pilot-rated witness, preparing a glider, observed the accident flight. He noted a normal taxi and engine run-up. The airplane then taxied onto the runway, increased power, and began the takeoff roll. The airplane rotated normally but continued rolling without climbing. At mid-runway, the witness suspected the airplane might be overloaded as it had not yet lifted off. When the main gear finally left the runway, the airplane appeared to "wallow." At about 50 feet, the landing gear retracted. The nose pitched down slightly, and the airplane began to sink in a "stall-like mush descent." The engine sounded as if producing full power. The airplane drifted left of the runway and descended out of view. The witness then heard impact and the engine stop instantly. He did not hear any loss of engine power during the takeoff.
Personnel and Aircraft Information
The pilot held a private pilot certificate with single-engine land rating, reporting 280 total flight hours, with 96 hours in the accident make and model.
The pilot provided preflight weight and balance computations to the FAA. He listed front seat occupants at 340 pounds, third and fourth seats at 245 pounds, fifth and sixth seats at 230 pounds, no baggage, and 185 pounds of fuel. The calculated total ramp weight was 3,668 pounds. After subtracting 20 pounds for fuel used during start, taxi, and run-up, the calculated takeoff weight was 3,648 pounds, just below the maximum gross takeoff weight of 3,650 pounds. The calculated takeoff distance required for the conditions was 900 feet, with 1,900 feet to clear a 50-foot obstacle.
The pilot's mechanic reported performing maintenance about one year prior. The pilot had experienced a partial loss of power on approach to a nearby airport, attributed to a broken exhaust valve spring. The mechanic provided a used exhaust valve spring from a previously removed cylinder and installed it. A log entry dated November 14, 2010, stated: "Replaced the #4 exhaust valve spring set with a serviceable set of springs." No other maintenance documentation or service history for that spring was available.
Meteorological and Airport Information
Weather at HRJ at 1255 included clear skies, wind from 130 degrees at 5 knots, temperature 23°C, dew point 6°C, altimeter 30.34 inHg, and density altitude 708 feet. The airport elevation was 202 feet. Runway 5/23 was 5,000 feet long by 75 feet wide, asphalt.
Wreckage and Impact Information
The airplane came to rest in a briar thicket off the left side of the runway. FAA inspectors found substantial damage to the fuselage. The left fuel tank was completely full, the right nearly empty. Fuel selector, magneto, and battery switches were off. The landing gear handle was down, the gear circuit breaker tripped, and flaps set to approach. When electrical power was applied, the red gear-in-transit light illuminated. The airplane was removed for further evaluation.
The mechanic assessed the engine at the FAA's request. He found the number 4 cylinder exhaust valve spring broken in two places. The engine was shipped to the manufacturer for examination. Crankshaft-to-camshaft timing was correct. Both magnetos produced spark on all leads. Spark plugs showed normal wear. The engine-driven fuel pump, fuel control assembly, and fuel manifold valve functioned properly on bench tests.
All six cylinders had normal combustion deposits, bore conditions were undamaged, and cylinder skirts were intact. Intake and exhaust valve heads had normal deposits and operating signatures. Rocker box areas had oil residue indicating upper cylinder lubrication. All valve springs were intact and undamaged except the number 4 cylinder exhaust valve springs: both inner and outer springs were fractured.
The fractured springs were examined in detail. Hardness testing showed no anomalies. Both springs had rust pitting on exterior surfaces. The inner spring had one fracture; the outer spring had two. Fracture surfaces showed post-separation damage obscuring some features. The inner spring's outer surface exhibited a fatigue crack with arrest lines originating from one or more pits. One origination pit contained iron oxide.