WPR24FA226

The pilot’s exceedance of the airplane’s critical angle of attack while maneuvering to avoid trees, which resulted in an aerodynamic stall.

The pilot planned to depart on his fourth flight of the day. Witnesses reported that the engine run-up, departure, and climbout were normal. When the airplane reached about 500 ft above ground level and was about 0.5 nautical miles (nm) south of the runway, the airplane entered an abrupt left bank, which was immediately followed by a spin before it impacted the ground in a nose-low attitude. Postaccident examination of the engine and flight controls did not reveal any preimpact mechanical anomalies. Witness reports indicated that the engine power was smooth and continuous and then ceased just before the airplane impacted trees. As the propeller damage signatures showed limited to no rotation at the time of impact, the pilot likely reduced the throttle during the descent. In addition, the gascolator sump valve was found in the open position. However, a witness did not observe any fuel leaking from the airplane during taxi or takeoff; thus, the sump valve position was likely a result of the impact. An examination of the engine controls revealed that the mixture control cable had separated at the carburetor. A metallurgical examination did not yield sufficient evidence, on its own, to determine whether the separation occurred prior to the accident. While there was evidence that the mixture cable attachment was worn and may have been slipping before the accident flight, the fracture surfaces showed overstress fracture features that could have occurred during the accident. If the fracture had occurred before the accident, it likely would have required at least one instance of aggressive use of the controls to cause the initial buckling of the control cable. However, evidence showed the pilot was able to adjust engine power during the descent, which suggests the cable failure likely occurred during the impact, and not before. The airplane’s precise fuel quantity at the time of the accident could not be determined, as the pilot also used a personal fuel trailer that did not contain any fuel records. Fuel receipts indicated that the pilot had most recently refueled the airplane at a nearby airport three months prior to the accident. Fuel performance computations showed that he likely filled the tanks to their total capacity during his last refueling, which would have left him with about 18 gallons of fuel on the day of the accident. This was sufficient to complete the estimated 30-minute scenic flight but would have placed the airplane about 40 lbs over its gross weight. The airplane was in a nose-high attitude about 10 ft above trees and approaching rising terrain when it stalled. The airplane impacted the ground after the pilot attempted to avoid the trees by entering a rapid left bank and a pitch attitude that exceeded the airplane’s critical angle of attack, which resulted in an aerodynamic stall and a loss of control.

Autopsies of the pilot and passenger were completed by the Pierce County Medical Examiner’s Office, Tacoma, Washington. According to the autopsy reports, the cause of death for both occupants was blunt-force injuries. Toxicology testing by the FAA forensic sciences division did not identify any substances of abuse in any of the samples submitted for the pilot and passenger. On July 6, 2024, at about 2122 Pacific daylight time, a Champion 7GCBC airplane, N3464D, was substantially damaged when it was involved in an accident near Swanson Airport (2W3), Eatonville, Washington. The pilot and passenger were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot’s wife, the pilot had volunteered to take the passenger, an acquaintance, on a local flight. Despite having an obscured view of the runway, she recalled that the airplane departed about one-quarter to one-third down the runway. She noted that engine run-up sounded normal. A witness (witness 1 in figure 1 below), located about 1 mile southwest of the airport, observed the airplane after it passed the departure end of runway 16 and tracked the runway heading. He recalled that the climbout appeared to be normal until about 0.5 to 1 mile south of the runway when the airplane was about 1,200 to 1,300 ft mean sea level (msl). At this time the airplane abruptly banked left about 45°, which was immediately followed by a quick right bank. The airplane entered a spin and did not recover. Another witness (witness 2 in figure 1 below), who was located about 500 ft southwest of the departure end of runway 16 at 2W3, stated that he heard the airplane perform an engine run-up and then take off. The airplane overflew his location at an altitude that was lower than he expected. The witness added that after the airplane flew out of his line of sight, he heard the airplane’s engine “cut out,” followed by the sound of a crash. Two additional witnesses, who were about 1,900 ft northwest of the accident site, observed the accident airplane flying southbound. Both witnesses described the airplane as being about 10 ft above the treetops and lower than an adjacent ridgeline. The witnesses said that the airplane was slow as it maintained a nose-high attitude, and the engine was producing smooth and continuous power. The airplane then performed a turn to the left, rolled inverted, and disappeared out of their line of sight below a tree canopy. The witnesses added that the sound of the engine stopped before the airplane impacted trees. Figure 1: The location of the witnesses with a depiction of the airplane’s approximate flight path The airplane came to rest in a nose-down attitude within a forested area about 0.5 nm south of the departure end of runway 16. All major components of the airplane were accounted for at the accident site. The airplane exhibited extensive impact damage and aft-crush deformation to the forward portion of the fuselage and the leading edges of both wings. The wings remained partially attached to the fuselage and the tail section was folded upward and to the left. Both the engine and propeller were buried in the ground beneath the wreckage. A noticeable fuel odor consistent with aviation gasoline was observed beneath the cockpit and left wing. The accident site was at an elevation of 803 ft msl, with rising mountainous terrain to the south and east that varied in elevation between 1,200 ft and 1,400 ft msl. Figure 2: The airport and terrain ahead of the runway departure end and near the accident site Postaccident examination of the engine did not reveal any preimpact mechanical anomalies or malfunctions that could have precluded normal operation. The aileron, elevator, and rudder flight controls were traced from the flight control stick to their respective flight control surfaces through multiple overload separations. The mixture control cable was found separated at the carburetor mixture control arm. A metallurgical analysis of the fracture surface revealed that the surfaces had dimple features consistent with a ductile overstress fracture. In addition, the fracture surface on the longer leg of the notch showed textured features with step-like terraces. The washer from the nut side of the mixture control arm had multiple cylindrical wear grooves consistent with wear against the control cable. The grooves associated with the tail piece and the control side of the cable at the time of fracture are indicated near the 9 o’clock and 3 o’clock positions, respectively. Additional wear grooves from previous control cable positioning were noted near the 7:30 and 1:30 clock positions. At the 9 o’clock and 3 o’clock positions, the wear grooves were deepest and widest near the inside diameter of the washer. At the contact wear grooves associated with the previous installation position, the wear grooves were relatively deeper and wider at the outside diameter of the washer when compared to the grooves at the fracture positions. A review of the maintenance logbooks from 2017 to the most recent entries did not contain any references to the mixture control system. According to the airplane type certificate (TC) holder, the type design for the carburetor mixture control arm normally has a swivel function that lets the cable rotate in order to have mostly tension/compression loads in the cable. The TC holder noted that the support design shows “2 washers crushing a loop on the cable,” which is not consistent with the type design. Figure 3: Mixture control support arm at carburetor Fuel Quantity According to the pilot’s wife, he had flown the accident airplane at about 1000 local time and then flew to Chehalis-Centralia Airport (CLS), Chehalis, Washington, in his Cessna 172 at an unknown time and subsequently returned home about 1600 local time. The accident pilot flew his Cessna 172 one more time that day before he departed on the accident flight. According to the pilot’s operating handbook (POH), the airplane was equipped with two fuel tanks, each with a capacity of 19.5 gallons, for a total of 39 gallons, located in the wings. The POH also showed an average fuel consumption of about 9 gallons per hour. According to the pilot’s logbook, he completed a “fuel run” on April 17, 2024, at which time he purchased about 15 gallons of 100 low-lead aviation gasoline and accumulated a total of 1.3 flight hours. He completed one additional local flight in the airplane accident the following day, April 18, 2024, totaling 1.1 flight hours. The pilot’s wife noted that he had completed one flight of approximately 1.2 flight hours on the day of the accident. The pilot also used a personal fuel trailer to refuel his airplanes; however, it is unknown if he used the trailer to refuel the accident airplane on the day of the accident, as there were no fuel records. The airplane gascolator sump valve was found in the open position during the postaccident examination. A friend of the passenger who witnessed the takeoff noted that he did not observe any fuel leaking from the airplane during taxi or takeoff. The departure runway was bordered by ridges between 1,100 ft and 1,400 ft mean sea level about 0.5 nm from the departure end. The ridgeline ascended and arced to the northeast and descended to the west to an elevation consistent with the airport elevation at 2W3. According to the FAA chart supplement, runway 16 required a right traffic procedure. The area to the west of the airplane’s flight path and accident site was also flat and provided a clear route back to the approach end of runway 16. The accident pilot was employed as the airport manager at the time of the accident and lived on the airport property. According to the pilot’s wife, their airplanes were hangared at the airport on the same property as their residence. Weight and Balance The weight and balance were computed usi