NTSB Factual Report

HISTORY OF FLIGHT

On April 22, 2010, at 0917 mountain standard time, a Grumman-Schweizer G-164B, N48455, collided with a gate during an attempted takeoff near Buckeye, Arizona. Crawford Aviation Services was operating the airplane under the provisions of Title 14 Code of Federal Regulations Part 137, as an aerial application flight. The certificated airline transport pilot sustained minor injuries; the airplane sustained substantial damage to the fuselage and both wings. The flight departed the private dirt airstrip at 0917. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot reported that the airplane's 335-gallon capacity hopper was loaded with 250 gallons of liquid herbicide mixture, and that the fuel tanks were loaded to about 1/2 of their capacity with about 36 gallons of fuel.

The pilot stated that prior to takeoff he performed an uneventful preflight inspection and engine run-up. He began the takeoff roll to the south in quartering headwind conditions, and about 2/3 of the way down the 2,500-foot-long runway, he heard the pitch of the engine change. He checked the engine speed, and noted it was about 2,080 rpm; he would normally have expected 2,250 rpm at this point during the takeoff roll. He confirmed the propeller control was in the full forward position, and observed the engine manifold pressure to be just below 36 inches. He increased the throttle control input; however, the engine speed did not increase, and was now at 2,040 rpm. He stated that the airplane had not yet taken off, and the airspeed was beginning to stagnate. He attempted to force the airplane airborne with control inputs, and it subsequently struck a fence at the end of the runway. The airplane then nosed over. The pilot reported that he did not release the herbicide load during the ground roll because he was concerned that the airspeed was too low, and that the airplane could potentially pitch-up in an uncontrolled manner.

AIRPLANE INFORMATION

The fixed-gear, tailwheel equipped biplane, serial number 28B, was manufactured in 1976. A review of the airplane’s maintenance logbooks revealed that at the time of the last annual inspection, dated September 18, 2009, the airplane had accrued a total time of 15,268.06 flight hours, with a recorded tachometer time of 1,395.45. The tachometer at the accident site indicated 1,452.09 hours.

The airplane was powered by a Pratt and Whitney R-1340-AN-1, single-row, nine-cylinder air-cooled radial engine, serial number 11075. The engine was equipped with a Hamilton Standard, three-bladed, constant speed propeller. Maintenance logbooks indicated that the engine was overhauled in September 2008, by Covington Aircraft, Okmulgee, Oklahoma. According to maintenance logbook records, at the time of overhaul, the 'estimated' engine total time was 8,750 hours. Based on the airframe tachometer time at the accident site, the engine had accrued 195.22 hours since the overhaul. Logbook records indicated that the last maintenance item performed was an oil and filter change on February 22, 2010, 37.92 flight hours prior to the accident.

TESTS AND RESEARCH

The engine and airframe were examined at the accident site by an inspector from the Federal Aviation Administration (FAA). The airplane came to rest inverted, about 200 feet beyond the departure end of the runway. The vertical stabilizer sustained impact damage, and had become folded against the horizontal stabilizer. Additionally, both the upper and lower wings sustained leading edge crush damage and spar twist. All three propeller blades sustained chordwise abrasions and leading edge gouges. One blade exhibited a 90-degree aft bend midspan; the remaining blade tips had become separated, revealing jagged tear features on their fracture surfaces. The propeller balance weights appeared firmly attached to each blade hub.

A visual examination of the engine revealed that it remained attached to its mounts, with no obvious holes in the engine case. The engine exhibited a bend in the number six cylinder pushrod cover at the housing connector, with damage noted to the number eight forward spark plug lead midspan, and a 1/4-inch wide by 1/2-inch deep gouge in the number three intake cowling support lug. The damage appeared consistent with impact.

The airplane was removed from the accident site and subsequently examined by the NTSB investigator-in-charge (IIC), and the FAA inspector. The fuel lines from the fuel shutoff valve through to the gascolator appeared intact and the fuel filter appeared free of obstructions. Movement of the throttle, carburetor heat, mixture, and propeller controls in the cabin resulted in corresponding full travel at each respective engine control arm. No obstructions were noted in the air induction system. No indications of cracks or holes were present in either the engine case, or the cylinder heads. The inner surfaces of the exhaust pipes exhibited tan-colored deposits, with no indication of oil residue or sooting. No mechanical anomalies were identified during the examination of the airframe.

The engine was removed from the airplane, and transported to Covington Aircraft for further examination in the presence of the NTSB IIC and an FAA inspector.

The forward spark plugs were removed and examined; the electrodes appeared dark grey in color, with slight ovaling of the electrodes consistent with normal wear signatures when compared to the Champion Aviation AV-27 Check-A-Plug chart. Rotation of the engine by hand via the crankshaft resulted in smooth movement with no binding noted. Thumb compression was attained for all cylinders. Removal of the rocker covers revealed the internal surfaces to be oil-wetted. Each valve assembly was examined, and no excess play or binding was noted. The valve spring compression was then checked utilizing a compression lever; full valve travel was achieved with no binding.

Removal of the governor revealed the filter screen to be clear of debris. Further rotation of the engine via the crankshaft confirmed drive-train continuity through to the blower, magnetos, starter and alternator gears, and governor spline.

The magneto ignition timing was checked, with the left and right magneto spark advance observed at 23.5, and 23 degrees before top dead center, respectively. The magnetos were removed and examined with no defects noted. The magnetos were subsequently mounted in a test stand, and spun to a rotational speed of 2,000 rpm. Both magnetos produced sparks at their respective lead outputs.

The valve timing clearance was visually checked, and corresponded to the value noted on the engine data plate. Removal of the engine nose case revealed the intake and exhaust tracks to be intact, free of gouges, cracks or abrasions. All gears appeared oil-wetted, with all teeth intact. The oil screen remained free of large obstructions, and contained about 1/4 teaspoon of fibrous lint debris, and dark colored deposits.

The rear accessory case was removed, and the lower impeller was inspected. The impeller appeared free of gouges or indications of distress. Removal of the impeller and cover plate revealed the plain bearing lower oil seal. The seal appeared oil-wetted and free of gouges, nicks, or indications of heat damage.

Visual examination of the carburetor revealed no indications of damage. The fuel idle mixture jets were observed about one notch short of maximum rich. Removal of the carburetor fuel inlet screen revealed it to be free of debris. The carburetor was then mounted on an exemplar Pratt and Whitney 1340 series engine, which was mounted in a test cell. The engine was then started, and operated through speeds varying between 500 and 2,250 rpm. A magneto comparison check was performed at both 1,800 and 2,000 rpm, with an acceptable nominal drop for both magnetos of between 80-90 rpm.

No mechanical anomalies were identified during the examination. A full report with photographs is contained within the public docket for this accident.

NTSB Probable Cause

A partial loss of engine power during the takeoff roll for undetermined reasons.