North Pole, AK, USA
N2746D
CESSNA 170B
During the takeoff of the personal flight, the airplane was unable to gain enough altitude to clear the trees off the departure end of the runway. Subsequently, the airplane impacted the trees and came to rest inverted, and a postaccident fire ensued, which destroyed the airplane. The pilot told the responding law enforcement officer that he thought that the wind had shifted during the takeoff and that the airplane lost lift at the end of the runway. A postaccident examination of the airplane revealed no evidence of preaccident mechanical malfunctions or failures that would have precluded normal operation. At the time of the accident, the airplane was departing from a grass/turf-covered runway, during a hot summer day, with full main fuel tanks, with a total of four occupants on board, and an estimated density altitude of 2,186 ft above mean sea level. The pilot reported that the airplane was about 13 pounds more than its maximum gross takeoff weight. The airplane owner’s manual indicated that at a maximum gross weight the airplane would need an estimated takeoff distance of 2,250 ft to clear a 50-ft obstacle. The accident site is a 2,400 ft long, by 100 ft wide, turf-covered site. The airplane manufacturer added that the turf runway would likely add to the distance needed for the takeoff. Thus, given the conditions of the accident, the pilot likely exceeded the airplane’s takeoff performance limitations, which resulted in the airplane not attaining the altitude needed to clear the tree line during takeoff and the subsequent impact with trees.
On July 1, 2021, about 1400 Alaska daylight time, a Cessna 170B airplane, N2746D, was destroyed when it was involved in an accident near North Pole, Alaska. The pilot and three passengers were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The airplane departed from Dalrymple’s Airport (31AK,) Fairbanks, Alaska. The pilot reported that the airplane was about 13 pounds more than its maximum gross takeoff weight. After completing the preflight check, the pilot initiated the takeoff roll with "1 notch” of flaps deployed. During the takeoff roll, when the airplane’s speed was about 40 to 45 mph, the pilot added a ”2nd notch” of flaps and climbed the airplane to tree top level “after using 1,000 ft of runway.” The pilot was unable to increase airspeed or altitude “without overly increasing the angle of attack” and noticed the airplane was not going to clear the trees off the end of the runway. He deployed full flaps, slowed the airplane to about 40 mph, and the airplane “settled in between trees” about 200 ft beyond the end of the runway. The airplane came to rest upright in a wooded area off the departure end of the runway with the nose of the airplane pointed back toward the runway. A postcrash fire ensued. A witness reported that she observed the airplane take off and climb to an altitude of about 100 ft above the trees at the departure end of the runway. The airplane then made a sharp left turn, the left wing impacted a tree, and the airplane descended into terrain. She further stated that the airplane’s nose did not drop during the left turn. The witness added that the airplane sounded normal throughout the takeoff and accident sequence with no unusual sounds and that the engine appeared to be operating. A law enforcement officer who responded to the accident reported that the pilot stated that he was not sure what happened during takeoff. The pilot thought that the wind had shifted, and that the airplane lost lift at the end of the runway. Postaccident examination of the airplane revealed no evidence of preaccident mechanical malfunctions or failures that would have precluded normal operation. The estimated density altitude for 31AK at the time of the accident was 2,186 ft above mean sea level. The airplane owner’s manual indicated that the airplane would need an estimated takeoff distance of 2,250 ft to clear a 50-ft obstacle. AK31 is a 2,400 ft long, by 100 ft wide, turf-covered site. The airplane manufacturer added that the turf runway would likely add to the distance needed for the takeoff. The Federal Aviation Administration (FAA) Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25B) discussed the effects of weight on an aircraft and stated in part the following: The pilot should always be aware of the consequences of overloading. An overloaded aircraft may not be able to leave the ground, or if it does become airborne, it may exhibit unexpected and unusually poor flight characteristics. If not properly loaded, the initial indication of poor performance usually takes place during takeoff. Excessive weight reduces the flight performance in almost every respect. For example, the most important performance deficiencies of an overloaded aircraft are: • Higher takeoff speed • Longer takeoff run • Reduced rate and angle of climb… • Reduced maneuverability • Higher stalling speed… • Excessive weight on the nose wheel or tail wheel The pilot must be knowledgeable about the effect of weight on the performance of the particular aircraft being flown. Preflight planning should include a check of performance charts to determine if the aircraft’s weight may contribute to hazardous flight operations. Excessive weight in itself reduces the safety margins available to the pilot and becomes even more hazardous when other performance-reducing factors are combined with excess weight. The FAA published Density Altitude (FAA-P-8740-2). This document stated that “Density altitude is formally defined as ’pressure altitude corrected for nonstandard temperature variations’.” The document also stated in part the following: The formal definition of density altitude is certainly correct, but the important thing to understand is that density altitude is an indicator of aircraft performance. The term comes from the fact that the density of the air decreases with altitude. A ’high’ density altitude means that air density is reduced, which has an adverse impact on aircraft performance…. Whether due to high altitude, high temperature, or both, reduced air density (reported in terms of density altitude) adversely affects aerodynamic performance and decreases the engine’s horsepower output.
The pilot’s exceedance of the airplane’s takeoff performance limitations, which prevented the airplane from gaining sufficient altitude to clear the trees off the departure end of the runway.
Source: NTSB Aviation Accident Database
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