MIA05LA127
MIA05LA127

On July 1, 2005, about 0630 eastern daylight time, an Air Tractor 502, N4515V, registered to Southeastern Aircraft Sales and Service Division, operated by Southeastern Aerial Crop Service, Inc., collided with trees following a reported partial loss of engine power during takeoff from Southeastern Airport, Fort Pierce, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR part 137 local, aerial application flight from Southeastern Airport. The airplane was substantially damaged and the commercial-rated pilot, the sole occupant, sustained minor injuries. The flight was originating at the time of the accident.

The pilot stated that the accident occurred during the first flight of the day; both fuel tanks were full, and the hopper tank contained approximately 425 gallons of chemical. The engine was started normally, after which, he cycled the propeller control one time. He taxied the airplane to depart from runway 27, and with one notch of flaps selected, applied power and noted the engine was producing 1,650 pounds of torque. The takeoff roll commenced, and when the aircraft was approximately 3/4 down the 2,600 foot-long runway, he noticed the airplane was "dragging a little bit." He noticed that the torque was down to 1,600 pounds, and attempted to dump the load in the hopper, but was unable because the handle would not move. He continued the takeoff and the airplane became airborne, but settled on a road. The aircraft collided with trees in an orange grove past the departure and of runway 27.

Another pilot for the operator who witnessed the accident reported that the takeoff roll seemed normal until the point where the airplane was too far down the runway with all landing gears on the ground. The airplane appeared to be flying at a high rate of speed but it was, "...not in flying configuration when he went past me, which was approximately 100 feet from the end of the runway. The tail wheel was just coming off the ground but the mains were still on. The engine seemed to be developing full power by the sound, but I do not recall seeing any flaps extended. Right at the end of the runway, he forced the airplane into the air, clearing the road by only a foot or two."

Examination of the accident site and airplane by an FAA aviation safety inspector revealed the airplane contacted a rise on the runway overrun area, collided with a fence that borders an orange grove past the departure end of the runway, then collided with trees. The airplane came to rest approximately 4,100 feet from the point where the takeoff roll commenced. The propeller was separated from the engine, and the hopper tank was empty due to impact damage.

The operator reported that postaccident, the hopper dump tested satisfactory, and the flap actuator jack screw measured .75 inch, while 2.0 inches equates to 10 degrees extended.

Cursory examination of the engine following recovery of the airplane by a representative of the engine manufacturer with FAA oversight revealed the P3 line (compressor discharge air) from the P3 filter to the fuel control unit (FCU) was found loose approximately 2 flats of the b-nut at the fuel control attach fitting. The oil quantity was determined to be 4.5 quarts. Impact damage to various components was noted. The engine was removed from the airplane and shipped to the manufacturer's facility in Canada for further examination.

Examination of the engine with Transportation Safety Board (TSB) of Canada oversight revealed impact damage to the engine and several engine accessories precluded operation in a test cell. The reduction gearbox forward housing was separated at the "A" flange; a portion of the gearbox flange remained secured at the "A" flange location. The propeller shaft was "intact", and the gas generator case displayed buckling in the area of the compressor assembly. The inlet line at the fuel control unit (FCU) was pulled from the FCU adapter. The propeller reversing interconnect linkage was fractured adjacent to the "A" flange location. The compressor discharge air (P3) line was continuous and pressure tested satisfactory from the gas generator case to the fuel control. The power turbine control (Py) line was continuous from the FCU to the forward fireseal, but the line was fractured in tensile overload near the propeller governor. The reduction gearbox ship detector exhibited some "metallic fuzz", while the oil and fuel filters were free of contaminants. Analysis of the fuel in the fuel filter housing revealed the specimen was within limits for water and solid contaminants. Examination of the compressor revealed the first stage exhibited tip rubbing, erosion near the blade platform, a "bur" at the blade tips, and the leading edges were "rough." The second and third stage compressor blades did not show any impact damage. The centrifugal impeller blade tips and the centrifugal impeller shroud exhibited circumferential rubbing. The Nos. 1 and 2 bearings and airseals were examined; the bearing housing of the No. 1 bearing was distorted at the mating flange, while the No. 2 roller bearing was "intact." Both bearing air seal rotors exhibited rubbing over its complete circumference. The combustion chamber liner and large exit duct both exhibited normal flame pattern. The compressor turbine guide vane ring and compressor turbine shroud exhibited rubbing; the compressor turbine blade airfoils were "intact" but some tip rubbing was noted. Circumferential rubbing of the downstream side of the disc face was noted near the blade fixing area, and the upstream face of the blade platforms were rubbed. Metal splatter was noted on the leading edges of the power turbine guide vane ring. The power turbine shroud was "rubbed, deformed, and battered", and all of the power turbine blades were fractured in the airfoil area. Metallurgical examination of the fractured blades revealed no evidence of preexisting fracture or overheating. The power turbine shaft was not fractured but the shaft coupling was bent. Examination of the reduction gearbox and accessory gearbox revealed no evidence of preimpact failure or malfunction. The exciter box was not returned with the engine; therefore it was not examined. The ignition leads exhibited localized fretting of the external braiding, and the ignition plugs were "intact." The engine controls were removed for further examination.

Examination and/or bench testing of the engine controls was performed at the engine manufacturers facility with TSB of Canada oversight. Bench testing of the fuel pump at 810 and 6,350 rpm revealed the outlet flow in terms of pounds-per-hour (pph) was 117 and 1,123 pph respectively (specification is 140 and 1,181 pph). Disassembly of the pump revealed slight wear in the gear teeth and bearings. Impact damage to the inlet threads of the FCU precluded bench testing. Disassembly of the FCU revealed the height of the bellows was within .0072 of the dimension marked on the bellows end. Bench testing of the starting flow control unit revealed the pressurizing valve opening pressure was recorded to be 85 psig (specification is maximum 80 psig). Bench testing of the fuel nozzles revealed the flow rates for all was acceptable, but the spray angle for nozzle Nos. 9 and 14 were above test limits. The opening flow pattern is acceptable for all but the No. 6 nozzle. Streaking was noted on the Nos. 1 and 2 nozzles, while "drooling" was noted on nozzle Nos. 1, 2, 4 and 6. Bench testing of the compressor bleed valve revealed the pressure required to close the valve (25.4 psia) was greater than specification which is 22.0 psia. Disassembly of the propeller overspeed governor and propeller governor revealed no evidence of preimpact failure or malfunction.

The engine was manufactured in February 1980 by Pratt & Whitney Canada, as a model PT6A-15AG engine, and designated serial number PC-E 14025. On January 6, 1992, the engine was converted to a model PT6A-34; the engine total time since new at that time was 5,976 hours. The engine modification increased the shaft horsepower from 680 to 750, and also increased the torque in terms of foot pounds (Ft.-Lb.) from 1,628 to 1,795. The engine was last overhauled on December 11, 1997; following overhaul the engine was installed in the accident airplane and was not removed until postaccident. Between the overhaul date and the accident date, several hot section inspections had been performed. The last hot section inspection occurred on February 10, 2004. At the time of the accident, the engine total time since new was 11,818.8 hours, the time since major overhaul was 2,867.8 hours, and the time since the last hot section inspection was 511.8 hours.

A review of revision 10 of the airplane type certificate data sheet (TC Data Sheet) for the make and model airplane (AT-502), revealed that with the make and model engine installed (PT6A-34), the maximum torque is 1,795 foot pounds for all operations. NTSB review of pictures provided by the FAA inspector revealed that with respect to the torque gauge, green colored tape was located on the glass on the instrument with the edge of the tape at approximately 1,750 foot pounds of torque. As previously reported by the pilot, after applying takeoff power the maximum torque achieved was 1,650.

The operator provided a sheet titled, "Turbine Trend Monitoring Report, Engine Model PT6-34" for the accident airplane which lists on specified dates various engine parameters including takeoff torque. The last recorded takeoff torque reading occurred on June 23, 2005, or approximately 8 days before the accident, and was listed as "1,750."

A review of the "Take-Off (Full Hopper Load And Short Field)" procedures section of the airplane flight manual revealed that the flaps are to be extended 10 degrees. As previously reported, postaccident the flaps were found between 0 and 10 degrees.

The airplane minus the retained engine was released to Rick Stone, V.P. of Southeastern Aerial Crop Service, Inc., on August 24, 2006. The NTSB retained engine was also released to Rick Stone on August 24, 2006.

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