Accident Overview
On August 12, 2021, about 1100 mountain daylight time, a Beech 77 (N3873Y) sustained substantial damage during a forced landing near Stanley, New Mexico. The pilot, who was the sole occupant, was not injured. The airplane was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Flight History
The pilot departed Double Eagle II Airport (KAEG) in Albuquerque, New Mexico, at about 1000. The atmospheric conditions at departure resulted in a density altitude of approximately 8,000 ft. During the climb, the airplane maintained a 200-foot-per-minute (fpm) rate of climb. The pilot noted that three days earlier, under similar atmospheric conditions and airplane loading, the climb rate had been 500 fpm. The airplane would not climb above 6,700 ft mean sea level, prompting the pilot to maneuver toward the destination airport.
Forced Landing
While maneuvering about 300 ft above ground level to the southeast to follow a road, the pilot observed the terrain rising and elected to perform a forced landing. Shortly after touchdown, the airplane impacted a cattleguard post and slid about 200 ft before stopping. The right wing sustained substantial damage.
Performance Data
Performance calculations from the pilot's operating handbook for the accident takeoff indicated that, given a pressure altitude of 5,527 ft, outside air temperature of 24°C, airplane weight of 1,645 lbs, flaps at 0°, mixture leaned to maximum rpm, and power at full throttle, the airplane's rate of climb should have been about 475 fpm.
Postaccident Examination
Examination of the airframe revealed no anomalies or malfunctions. Examination of the engine established mechanical continuity throughout the engine and valve train. The top spark plugs were carbon fouled and displayed black, sooty deposits, while the lower spark plugs were heavily lead fouled and displayed hard, cinder-like globules of lead around the firing end and cavity. According to the pilot, he believed he had an undetected fouled plug.
Spark Plug Condition
According to the Champion Aerospace Aviation Service Manual, severely fouled spark plugs will operate colder, causing misfires, and will also misfire at higher power because of the conductive nature of the deposits at elevated temperatures.
Maintenance History
According to the engine logbooks, all spark plugs were cleaned and gapped during the most recent annual inspection about one year before the accident.