NTSB Factual Report

On March 13, 2016, about 0800 mountain daylight time, N4696B, a taiwheel equipped Cessna 180, was substantially damaged when the airplane failed to accelerate and overran the end of the runway surface while attempting to take off from a private airstrip about 2 nautical miles west of Boulder, Utah. The commercial pilot, who was the owner of the airplane, and his two passengers were not injured. Visual meteorological conditions prevailed for the planned local flight, which was being operated in accordance with 14 Code of Federal Regulations Part 91, and a flight plan was not filed. The flight was originating at the time of the accident.

In a report submitted to the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that prior to departing, he allowed the engine to warm up for about 15 minutes. He also rechecked the magnetos, listened to the engine at higher power settings, and due to the airstrip being dirt, did not check the carburetor heat; normal oil pressure was observed. The pilot stated that after he applied full power and started the takeoff roll [to the west] on the 2,100 foot unimproved dirt airstrip, he observed the acceleration to be "ok", but felt a little slow. The pilot added that he thought the dirt might have been soft, or that the vegetation was slowing the airplane down, but when he glanced at the tachometer it was reading right at the redline, 2,600 rpm; he did not remember looking at the manifold pressure gauge, nor did he report the engine running rough or backfiring. The pilot opined that about one-half to two-thirds of the way down the runway the tail lifted off the runway's surface, at which point he added one notch of flaps as the airplane continued to roll on its main landing gear. The pilot reported that as the end of the airstrip approached he pulled back on the control yoke, which resulted in an increase in the angle-of-attack. The airplane subsequently lifted about two feet off the runway surface before settling into the sagebrush. The pilot stated that when he attempted to reduce power by retarding the throttle, the engine continued to run at the same high-output level. As the airplane continued to roll it was slowed by the vegetation, and subsequently impacted a 10-foot diameter tree before coming to rest upright about 50 yards from the tree stump. The pilot stated that he suspected that the engine was not generating full power, and that he could have aborted the takeoff at that time. The pilot reported that winds were from the northwest at 5 knots. A postaccident examination of the airplane revealed substantial damage to both wings and the elevator. The airplane was recovered to a secure location for further examination.

On April 27, 2016, under the supervision of the NTSB IIC, a Continental Motors Inc. field technician performed an examination of the engine at the facilities of Air Transport, Phoenix, Arizona.

The engine remained attached to the airframe via the engine mount legs. No external damage was noted. The top spark plugs were removed and exhibited grey combustion deposits. The electrodes had normal, worn out signatures. The cylinder combustion chambers were examined with a lighted borescope, with no anomalies noted. The crankshaft was rotated by hand using the propeller, with thumb compression confirmed on all six cylinders. The magneto impulse couplings were audible, and spark was produced on all six top spark plug leads.

In preparation for a test run of the engine, an external fuel supply was plumbed into the right wing root fuel line. The fuel selector was placed in the right hand position for the first engine run.

After the engine was started and allowed to warm up, the throttle was advanced to 1,600 rpm and a magneto check performed; each magneto dropped about 75 rpm. When the throttle was advanced full forward, the engine obtained 2,600 rpm and 22 inches of manifold pressure. The throttle was then reduced to idle to allow the engine to cool down before it was secured using the mixture control. No binding of the throttle or mixture controls was noted during the engine run.

The fuel supply was then plumbed into the left wing root fuel line to verify proper operation of the fuel selector in the left hand position. The engine was then restarted and ran normally. When the selector was placed in the "both" position, the engine continued to run normally. The fuel selector was then moved to the "off" position, and after several seconds it began to run rough. The fuel selector was subsequently positioned to the left tank position, from which it ran smoothly. The engine was allowed to cool down at idle before a normal shut down was accomplished using the mixture control lever.

On April 27, 2017, at the facilities of Air Transport, Phoenix, Arizona, the NTSB IIC performed an examination of the airframe. No anomalies were noted during the examination.

The postaccident examination of the engine and airframe failed to reveal any anomalies that would have precluded normal operation.

NTSB Probable Cause

The pilot's failure to abort the takeoff from the soft runway surface, which precluded optimal acceleration during the takeoff sequence.