N509HB

On June 3, 2023, about 1158 central daylight time, an Air Tractor AT-502B airplane, N509HB, was substantially damaged when it was involved in an accident near Lake Village, Arkansas. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 137 aerial application flight.

The pilot reported that shortly after departure, the airplane lost thrust as the propeller moved towards a feathered position, but the engine remained operating. Unable to continue flight with diminished thrust, the pilot started to jettison fertilizer while he completed a forced landing to a field, which resulted in substantial damage to the fuselage, empennage, and both wings.

A review of maintenance records indicated that the airplane had undergone maintenance the preceding day at a 14 CFR Part 145 repair station, which included an adjustment to the propeller beta plunger. The extent of the work was not documented on the work order and no logbook entries were made in the logbook. During a postaccident examination, engine and propeller control continuity was established from the cockpit controls to their respective engine and propeller components with no anomalies noted.

There was no evidence of preimpact malfunction or failure with the propeller that would have precluded normal operation. All three propeller blades were bent aft, opposite the direction of rotation, and exhibited chordwise scoring and abrasion, all features consistent with high impact forces while rotating at low power and low blade pitch angle (not feathered). The beta system was exercised with a beta puller. It actuated smoothly and returned to the home position without hesitation.

The engine displayed contact signatures to its power turbine blades and vane ring consistent with the engine developing some degree of power at the time of impact. There was no evidence of any preimpact mechanical anomalies to any of the engine components that would have precluded normal engine operation. The fuel control unit, fuel oil heat exchanger, and fuel pump were submitted to Pratt & Whitney Canada for further analysis. The analysis found no preimpact anomalies that would have precluded normal operation.

Weather conditions recorded at the Mid Delta Regional Airport (GLH) located about 20 miles northeast of the accident site, at 1153, were: wind from 060° at 4 knots; clear of clouds; 10 statute miles visibility, temperature 31.1° Celsius, dew point 18.9° Celsius, and an altimeter setting of 29.85 inches of mercury. The associated station pressure was 29.71 inches of mercury. The calculated density altitude was 2,377 ft. The pilot departed to the south (180° heading).

A weight and balance data sheet completed on January 15, 2008, listed the airplane’s empty weight as 4,790.5 lbs. The hopper was filled with 2,900 lbs of fertilizer. The pilot reported that he had about 3/4 tanks of fuel on in each 85-gal wing tank totaling about 120 gallons of fuel. However, during an on-site inspection, an inspector from the Federal Aviation Administration (FAA) did not observe any visible fuel in the wing tanks. The inspector stated that the fuel tanks were not compromised or punctured and there were no visible leaks. There was no odor of fuel or any evidence of fuel soaking into the ground. The pilot and operator both stated that they did not remove any fuel before the FAA inspector arrived. Therefore, the amount of fuel on board the airplane at the time of the accident could not be definitively determined. With the available information, the airplane’s weight was estimated to be at or over 8,000 lbs. According to the Air Tractor Airplane Flight Manual, a takeoff weight under 8,000 lbs requires the flaps to be set to 10°, and a takeoff weight over 8,000 lbs requires flaps to be set to 20°. A review of accident scene photographs indicated the airplane’s flaps were set to about 20°.

Given the weather conditions at the accident site, with a calm wind condition, and using a minimum weight of 8,000 lbs and a maximum weight of 9,400 lbs, it is estimated that the airplane’s takeoff ground roll on a paved runway would have been between about 1,418 ft and 2,156 ft. The airstrip the pilot departed from was about 2,100 ft of paved surface. Unpaved surfaces, high density altitudes, and tailwinds would increase ground roll distance.

The Federal Aviation Administration (FAA) Pilot's Handbook of Aeronautical Knowledge (FAA-H 8083-25A) noted that density altitude represents pressure altitude corrected for nonstandard temperature. A decrease in air density corresponds with an increase in density altitude and a decrease in airplane performance. Density altitude is used in calculating airplane performance. The handbook also noted the effect of wind on takeoff distance is large, requiring proper consideration on takeoff performance. A tailwind of 10% of the takeoff airspeed will increase the takeoff distance about 21%.