Delaplaine, AR, USA
N8402K
GULFSTREAM-SCHWEIZER A/C CORP GULFSTREAM AM G 164B
The commercial pilot was conducting an agricultural application flight. The pilot reported that the airplane had been refueled before the preceding flight, which was about 15 minutes long and was completed without incident, and that the fertilizer load was about the same on the accident flight as it was on the preceding flight. He added that the accident takeoff ground run was longer than for the previous takeoff and that, after he became aware of the extended ground run, the airplane was already past his predetermined takeoff "commitment" (go/no go) point. The airplane became airborne but did not climb. The tailwheel subsequently impacted a rice levee, and the airplane then settled into the field and came to rest inverted. The pilot noted that he never actually lost control of the airplane and that he did not perceive any issues with the airframe or the engine during the accident takeoff. A postaccident examination of the engine and airframe did not reveal any preimpact mechanical failures or malfunctions. An engine teardown examination revealed evidence consistent with engine operation at impact. The examination also revealed that the torsion shaft had failed due to torsional overload as a result of a sudden stoppage of the engine at impact. The density altitude was calculated to be about 1,680 ft, and a light tailwind existed at the time of the accident. The airplane was likely operating at or near its maximum gross weight, which, combined with the effects of the elevated density altitude and light tailwind conditions, resulted in the airplane becoming airborne at an airspeed that could not be maintained outside of ground effect. The pilot subsequently failed to maintain the proper angle-of-attack as he attempted to climb the airplane out of ground effect, which resulted in an aerodynamic stall.
On June 3, 2015, about 1718 central daylight time, a Gulfstream-Schweizer A/C Corp. Gulfstream AM G-164B airplane, N8402K, was substantially damaged during an in-flight collision with terrain after takeoff from a private airstrip near Delaplaine, Arkansas. The pilot sustained minor injuries. The airplane was registered to and operated by Wilson Flying Service, Inc. under the provisions of 14 Code of Federal Regulations Part 137 as an agricultural application flight. Visual meteorological conditions prevailed for the flight, which was not operated on a flight plan. The local flight was originating at the time of the accident. The pilot noted that the gravel runway was about 2,300 feet long and oriented northeast-southwest. The accident takeoff was to the southwest. The runway was somewhat shorter than he normally used and the "thicker gravel" might have extended his takeoff runs. He had started flying about noon that day and had been flying for about 5 hours at the time of the accident. The airplane was refueled before the preceding flight, which was about 15 minutes in duration and was completed without incident. He added that the fertilizer load was about the same on the accident flight as it was on the preceding flight. The pilot reported that the accident takeoff ground run was longer than for the previous takeoffs. The ground run for the previous takeoffs had been about 1,700 feet. After he became aware of the extended ground run, the airplane was already past his pre-determined takeoff "commitment" (go-no go) point. The airplane became airborne; however, it did not climb. The tailwheel subsequently impacted a rice levee, causing the airplane to settle into the field. He never actually lost control of the airplane. The pilot noted that he did not perceive any issues with the airframe or the engine during the accident takeoff. The engine torque indication was normal when he checked it near the beginning of the takeoff roll. However, he did not recall checking it again because he was focused on flying the airplane. The airplane came to rest inverted in the open field. The nose and forward fuselage exhibited minor damage. The aft fuselage and empennage were deformed and separated from the remainder of the fuselage. The wings were deformed and dislocated relative to the fuselage. The upper, right wing section was separated from the upper, center wing section. The separated wing section was located adjacent to the airplane at the accident site. A postaccident examination was conducted after recovery of the airplane under the supervision of the NTSB investigator-in-charge. The wings had been removed in order to facilitate recovery. The engine and propeller remained attached to the airframe and engine, respectively. The upper and right side gearbox mounts were bent, but remained attached. The left side gearbox mount was separated from the airframe structure. The rear mounting bolt common to the combustor plenum was fractured. The separation appeared consistent with overstress failures. The propeller blades remained attached to the hub. All three blades were bent aft over the span of the blade. The tips of two blades had separated. At the time of the examination, the blades appeared to be in low-pitch position relative to the hub. An initial engine examination revealed a discontinuity between the propeller and the third-stage turbine. Deposits consistent in appearance with compressor shroud metal spray were observed on the aft sides of the third-stage turbine blades. The main fuel line was disconnected from the fuel pump inlet. A fluid consistent in odor and appearance with jet fuel was observed in the fuel line. Engine control continuity was confirmed, with the exception of the propeller feather valve. No linkage was connected to the feather valve at the time of the examination, nor was evidence of a control linkage to the feather valve observed. The engine was subsequently removed from the airframe and shipped to the engine manufacturer for a teardown examination. Teardown examination of the engine was conducted under the supervision of an NTSB investigator. Earthen (ground) debris was observed throughout the compressor, combustion, and turbine sections of the engine. Rotational scoring was observed in both the compressor and turbine sections of the engine. One first-stage compressor impeller vane was bent opposite the direction of rotation at the leading edge outer diameter consistent with foreign object damage. The combustion section was unremarkable, with the exception of the previously noted debris. The turbine section stator vanes and rotor blades exhibited suction-side metal spray deposits consistent with engine operation at impact. The examination revealed that the torsion shaft was sheared immediately forward of the aft splines. Metallurgical examination of the shaft revealed that it failed as a result of torsional overload. The shouldered (main) shaft appeared to be intact. No evidence of a loss of engine oil was observed. The fuel filter element appeared to be intact and free of debris. A fuel sample was recovered from the fuel filter assembly. Testing of the sample determined that it was consistent with Jet A aviation fuel. However, the sample contained small-particle debris of an undetermined origin. The amount of debris and the size of the particles appeared inconsistent with a loss of engine power. The fuel control unit was tested at the component manufacturer's facilities under supervision of the NTSB investigator-in-charge. During testing, the standard acceleration schedule fuel flows exceeded the specification by about 9-percent to the high-side at three test points in the engine start range, and was out of specification by about 1-percent to the low-side at one test point in the high power range. All remaining acceleration test points were within specification limits. Both the underspeed and overspeed fuel flows were lean (low) as compared to the specification limits. In order to achieve the required fuel flows, the input drive speeds were adjusted by 0.4-percent in the case of the underspeed governor, and up to 1.6-percent in the case of the overspeed governor. The main metering valve TT2 and PT2 correction schedules exhibited high-side deviations at maximum power settings of up to 13-percent and 20-percent, respectively. However, the TT2 correction fuel flow under standard day, maximum power conditions was within the specification. The PT2 correction fuel flow under the same conditions exceeded the specification to the high-side by about 3.6-percent. According to the manufacturer, this setting is commonly adjusted by the operator. The fuel pump was tested at the component manufacturer's facilities under supervision of an NTSB investigator. The fuel pump flow rates and discharge pressure were within the specification requirements when tested at both high speed (100-percent engine power) and at low speed (engine starting). Specifically, the flow rate corresponding to high engine speeds was 1,720 lbs/hr, as compared to a required flow rate of 1,400 lbs/hr minimum. The flow rate corresponding to low engine speeds was 148 lbs/hr, as compared to a required flow rate of 120 lbs/hr minimum. The discharge pressure measured 1,340 psi, as compared to a specification requirement of 1,375 psi maximum. The propeller governor was tested at the component manufacturer's facilities under supervision of the NTSB investigator-in-charge. During testing, the propeller governor maximum and minimum speeds exceeded those for a new, production component. The maximum speed measured 3,858 rpm, as compared to a specification range of 3,754 +/- 10 rpm. A reduction in the input lever angle of 14 degrees, from 139 degrees to 125 degrees was necessary to obtain the specified maximum speed. The minimum speed measured 3,665 rpm, as compared to a specification range of 2,815 +/- 10 rpm. A reduction in the input lever angle of 26 degrees, from 88 degrees to 62 degrees was necessary to obtain the specified minimum speed. In addition, relief valve pressure measured 11 psi below the minimum specification requirement of 445 psi. However, the pump case pressure remained within limits during the testing. All other test parameters were within specification limits. The component manufacturer noted that the maximum and minimum speed parameters are subject to in-service adjustment by the operator. The accident airplane, Gulfstream-Schweizer A/C Corp. Gulfstream AM G-164B (serial number 687B), was initially issued an airworthiness certificate in April 1982. NTSB records indicate that the airplane was involved in five prior accidents. The most recent occurred on August 22, 2013, in Walnut Ridge, Arkansas (NTSB case number: CEN13LA504). An airplane maintenance record entry, dated July 9, 2014, indicated that the airplane was disassembled and subsequently re-assembled using a repaired fuselage. The total airframe time associated with this entry was 12,381.6 hours. The most recent annual inspection was completed on February 2, 2015, at 12,381.6 hours total time airframe. The operator reported the airframe total time as 12,489.5 hours. The airplane was powered by a Honeywell/Airesearch TPE331-1-151A turboprop engine (serial number P-92108). The engine is a single-spool design with a two-stage, centrifugal compressor, reverse flow annular combustion section, and three-stage axial flow turbine. Maintenance records indicated that the engine total time was approximately 11,981.0 hours. The most recent annual inspection was completed on February 2, 2015, at 11,873.1 hour total time engine. The most recent engine hot section inspection was completed on May 9, 2014, at 11,873.1 total engine hours. The airframe and engine maintenance records did not contain a history of recurring or unresolved maintenance issues. The prevailing winds were from the northeast at 4 or 5 knots, which provided a light tailwind during the accident takeoff. In addition, the elevated air temperatures increased the density altitude to about 1,680 feet, as compared to a runway elevation of approximately 265 feet.
The pilot’s failure to establish a proper airspeed and angle-of attack during takeoff in elevated density altitude and light tailwind conditions, which resulted in an aerodynamic stall.
Source: NTSB Aviation Accident Database
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