Ardmore, TN, USA
N3962V
Cessna 170
The pilot, a passenger, and a dog were departing from a grass field. The pilot had purchased the airplane about 5 days before and this was the first time he had operated from the field. He reported that, after takeoff, there was “inadequate thrust” to climb, and he performed a forced landing to a pasture, during which the airplane sustained substantial damage. Postaccident examination of the airplane revealed that the wing flaps were in the retracted position. Examination of the engine revealed a partial fracture just aft of the propeller flange. The fracture was visibly twisted, and the fracture face displayed a 45° angle to the longitudinal axis of the crankshaft. This was indicative of an overload type of failure consistent with the impact, and that the engine was producing power during the accident sequence. The right magneto was also damaged during the impact, which precluded functional testing. Overall, the examination of the engine did not reveal evidence of any preimpact failures or malfunctions that would have precluded normal operation. The pilot believed that the field was about 2,000 ft long; however, review of satellite images indicated that the field was only about 1,230 ft long and sloped uphill. Obstacles existed along the departure path in the form of a driveway, trees, and buildings. Review of the airplane owner’s manual indicated that, for shortest takeoff the wing flaps should be in the “full down” (30°) position. It also noted that for unusually short field takeoffs, the application of wing flaps should occur just before the airplane is ready to leave the ground, and the flaps should not be retracted until an altitude of at least 100 ft above the highest obstacle. The density altitude around the time of the accident was about 3,224 ft. Under such conditions, the pilot would have experienced a takeoff distance about 34% longer than normal and an approximate 26% reduction in rate of climb. Review of performance information contained in the airplane owner’s manual revealed that, under similar atmospheric conditions, at maximum gross weight with the flaps retracted, the airplane would have required a takeoff ground roll distance of about 880 ft; however, this information was valid for a level, hard-surfaced runway. The distance to clear a 50-ft obstacle was about 2,200 ft. No performance information was published for operations off turf/grass surfaces, which provide more rolling resistance (drag) than paved surfaces. Based on the available information, it is likely that the airplane’s takeoff and climb performance was reduced due to the elevated density altitude conditions and the additional drag provided by the grass. Additionally, the pilot did not use the short-field takeoff technique prescribed by the owner’s manual. Had the pilot more thoroughly familiarized himself with the constraints of the area he was attempting to take off from, as well as the information provided in the owner’s manual, he likely would have realized that departing from the field under the accident circumstances provided little margin for a successful takeoff and climbout.
On August 13, 2020, about 1745 central daylight time, a Cessna 170, N3962V, was substantially damaged when it was involved in an accident near Ardmore, Tennessee. The pilot and passenger received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, along with his uncle and a dog, were departing from a grass field on a friend's property when the accident occurred. The pilot reported that he purchased the airplane about five days before the accident, and this was the first time he had operated from the field. He had about 10 to 15 gallons of fuel per side (20 to 30 gallons total) onboard prior to takeoff. The grass was dry, and the wind was calm. The engine run-up was normal. During the takeoff roll, when the airplane reached 50 to 60 mph, he rotated and established a climb rate. The airspeed then began to decay, and there was inadequate thrust to achieve an acceptable rate of climb at an adequate airspeed, and the pilot performed a forced landing to a small pasture. The pilot did not recall any changes in engine noise prior to the accident. Examination of photographs of the airplane provided by the Federal Aviation Administration (FAA) revealed that the left main landing gear collapsed, and the airplane impacted the ground with the left wingtip, nose, and right wingtip, and came to rest upright. The wing flaps were fully retracted, and the airplane incurred substantial damage to the engine mounts, firewall, wings, and fuselage. Examination of the engine revealed that the crankshaft displayed a partial fracture just aft of the propeller flange. The fracture was visibly twisted, and the fracture face displayed a 45° angle to the longitudinal axis of the crankshaft. Further examination of the engine also did not reveal any noticeable issues and drivetrain continuity, from the front to the back of the engine was established. All the pistons would move when the crankshaft was rotated. The top spark plugs appeared normal. The left magneto produced spark at all leads. The right magneto could not be turned by hand. Disassembly of the right magneto revealed that the impulse coupling shaft bearing was broken due to impact; however, it would move with difficulty by hand once the cap was removed. No damage to the coupling drive gear or any visible part of the gears seen through the accessory case was discovered. Fuel was present in the carburetor and the accelerator pump was functional. The fuel strainer was impact damaged. The pilot believed that the field that he tried to depart from was about 2,000 ft long; however, review of satellite images of the accident location indicated that the field was about 1,230 ft long. The elevation was about 896’ above mean sea level. Obstacles existed along the departure path the pilot flew (about 180°), in the form of a driveway, trees, and buildings. Past the driveway, the terrain was about 25 ft higher than the field, and the trees were in close proximity to the area where the airplane came to rest. Review of the Cessna Model 170 Owner’s Manual indicated that, for “shortest takeoff” the wing flaps should be in the “full down” (30°) position. For unusually short field takeoff, the application of wing flaps to the full down position should occur just before the airplane is ready to leave the ground, and the flaps should not be retracted until an altitude of at least 100 ft above the highest obstacle. The recorded weather at Fayetteville Municipal Airport (FYM), Fayetteville, Tennessee, located 13 nautical miles east of the accident site, at 1755, included wind from 150° at 3 knots, 10 miles visibility, clear sky, temperature 31°C, dew point 21°C, and an altimeter setting of 29.96 inches of mercury. The density altitude around the time of the accident was about 3,224 ft. Interpolation of performance information contained in the Cessna Model 170 Owner’s Manual revealed that, at maximum gross weight, zero wind, and flaps retracted, at the approximate elevation and temperature at the accident site, the takeoff distance to clear a 50-ft obstacle would have been about 2,205 ft with a ground run of 882 ft from a hard-surfaced runway. Review of an FAA Koch Chart revealed that at a temperature of 31°C, the pilot would have experienced a takeoff distance approximately 34% longer with an associated 26% decrease in rate of climb. Under these conditions, a runway of approximately 1,300 feet would be equivalent to an international standard atmosphere sea level runway length of 970 feet.
The pilot’s inadequate preflight planning and his decision to depart from a constrained, grass-covered field in elevated-density altitude conditions, which resulted in reduced takeoff and climb performance and a subsequent forced landing.
Source: NTSB Aviation Accident Database
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