CEN16FA116

The pilot's failure to maintain sufficient airspeed while maneuvering at low altitude in strong gusting winds, which resulted in exceedance of the airplane's critical angle of attack and an aerodynamic stall/spin. Contributing to the accident was the pilot's impairment due to the effects of a sedating antihistamine.

The commercial pilot and the pilot-rated passenger were flying the biplane to a fly-in gathering in another state. Witnesses saw the airplane flying over a frozen lake at a low altitude and low airspeed. One witness saw the airplane "listing" left and right before it entered a left turn, and he lost sight of it. Other witnesses saw the airplane turn left and nose-dive into the ground. A postimpact fire consumed most of the airplane. Damage to the wreckage indicated that the airplane impacted the ground in a nose-down attitude. The examination did not reveal evidence of any preimpact anomalies with the airframe, engine, or the control system of the airplane. A witness reported that, at the time of the accident, the wind was from the south about 30 miles per hour. However, a burnt area extending east from the airplane's impact point indicated the wind was from the west. Additionally, although wind information from nearby weather stations varied in direction and intensity. One station, about 14 miles west-northwest of the accident site reported calm wind., However, another station, located about 11 miles south of the accident site, recorded wind from the west at 11 knots with gusts to 27 knots about the time of the accident and wind from the west at 33 knots with gusts to 48 knots about an hour after the accident. Further, the forecast for the accident area called for wind gusts to 40 knots from the west-northwest. Therefore, it is likely that strong gusty west winds prevailed in the accident area at the time of the accident. Although some witnesses speculated that the pilot may have been attempting to land the airplane on the frozen lake, the airplane was not equipped to land on ice, and the reason the pilot was maneuvering at a low altitude in strong gusty winds could not be determined. Based on the witness observations and the damage to the wreckage, it is likely that the pilot allowed the airspeed to decrease to a point where the critical angle of attack was exceeded, and the airplane entered an aerodynamic stall/spin. Although the pilot was known to have heart disease, it is unlikely that his medical condition contributed to the accident. The witness observations indicate that the pilot was actively flying the airplane before the loss of control. Toxicology testing showed the presence of chlorpheniramine in the pilot's blood at a level that was likely in the therapeutic range. Chlorpheniramine is a sedating antihistamine available in a number of over the counter products, and it carries the warning, "May impair mental and/or physical ability required for the performance of potentially hazardous tasks (e.g., driving, operating heavy machinery)." Because of its sedating effect, chlorpheniramine may slow psychomotor functioning and cause drowsiness. It has also been shown in a driving simulator (after a single dose) to suppress visual-spatial cognition and visual-motor coordinating functions when compared to placebo. Such functions would have been necessary for the pilot to maintain control of the airplane while maneuvering close to the ground in the strong gusty wind conditions. Therefore, it is likely that the pilot's ability to safely operate the plane was impaired by the effects of chlorpheniramine.

HISTORY OF FLIGHT On March 2, 2016, about 0800 mountain standard time, a Curtis Wright Travel Air 4000 airplane, N6464, was destroyed when it impacted the ground in an uncontrolled descent near Palmer Lake, Colorado. The pilot and the pilot-rated passenger were fatally injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight; no flight plan had been filed. Visual meteorological conditions prevailed near the accident site. The flight originated from the Vance Brand Airport, near Longmont, Colorado, about 0715. An acquaintance of the pilot reported that the airplane was en route to a fly-in gathering at the Casa Grande Municipal Airport, Casa Grande, Arizona. A witness, who had about 35 to 40 hours flight experience, reported seeing the airplane flying south over Palmer Lake at a low altitude and low airspeed. He stated that it appeared as if the airplane was making a "low slow scenic pass" over the lake. He said that the airplane was going "pretty slow," but it was flying south into a headwind of about 30 mph. He said that, while flying over the lake, the airplane started a left turn when it was near the south end of the lake at an altitude of about 200 ft above the ground. He said that the turn was about 20° to 30° in bank and that the airplane then "slid" before going out of view behind trees. He stated that as soon as he saw the airplane begin to turn he became very concerned. He drove to the scene and saw the airplane in flames. Another witness reported seeing the airplane heading south at a low altitude over the north end of the lake. He stated that the airplane seemed to be out of control, back under control, and then it turned toward the north. He speculated that the pilot may have been trying to land on the frozen lake. The airplane then turned to the south again, banked left, and nosedived into the ground. A third witness reported seeing the airplane flying above the lake. She reported that it seemed to "struggle" and then seemed to level out. The airplane then went out of control again, banked left, nosedived into the ground, and caught fire. A fourth witness reported seeing the airplane flying southbound over the railroad tracks, about 100 ft above the ground. He stated that the airplane seemed to be floating in the air and did not seem to have a lot of power. He further stated that the airplane was "listing left and right greatly." He saw the airplane turn toward the east just past the lake. The turn appeared to be controlled, and he thought the airplane was possibly trying to land. By this time, the airplane had descended to about 15 to 20 f above the ground. He did not see or hear the impact. PERSONNEL INFORMATION Pilot The pilot held a commercial pilot certificate with airplane single-engine land and airplane multiengine land ratings. The multiengine rating was limited to private pilot privileges. The pilot's most recent third class medical certificate was issued on June 10, 2013, with the following limitations: "Must wear corrective lenses. Not valid for any class after June 30, 2015." At the time of the accident, this medical certificate had expired for all classes and had not been renewed. The pilot reported having 5,000 hours total flight experience and 50 hours in the 6 months preceding his most recent airman medical examination. The pilot's flight logbooks were not available for review during the investigation. Pilot-rated Passenger The passenger held a commercial pilot certificate with airplane single-engine land, airplane single-engine sea, airplane multiengine land, and instrument airplane ratings. His most recent third class medical certificate was issued on October 14, 2010, with the limitation: "Must wear corrective lenses." At the time of the accident, this medical certificate had expired for all classes and had not been renewed. AIRCRAFT INFORMATION The airplane was a 1928 Curtis Wright Travel Air 4000 airplane. It was a two-seat biplane with a conventional (tailwheel) landing gear arrangement. The wings were constructed of wood with a fabric covering. The fuselage used a steel tube structure with fabric covering. A 235-horsepower Wright Whirlwind, model R-760-8, seven-cylinder radial engine powered the airplane. The most recent aircraft logbooks were not located during the investigation; however, the mechanic who certified the most recent annual inspection reported that it was completed on July 1, 2015. The type certificate data sheet for the Travel Air 4000 indicated that the airplane was originally equipped with a Wright J-5, 220-horsepower, nine-cylinder radial engine. Research for aircraft specifications relating to the accident airplane did not reveal those for an airplane with the same engine model installation as the accident airplane. Specifications found for a Travel Air 4000 with a 165-horsepower Wright J-6 radial engine were as follows: Engine: Wright J-6 "Whirlwind" five-cylinder radial, 165 hp at 1,800 rpm Length overall: 24 ft. 1 in. Height overall: 8 ft. 11 in. Wingspan (upper): 33 ft. Wingspan (lower): 28 ft. 9 in. Wing chord (upper): 5 ft. 6 in. Wing chord (lower): 4 ft. 8 in. Wing area (upper): 171 sq. ft. Wing area (lower): 118 sq ft. Gross weight: 2,702 lbs. Empty weight: 1,695 lbs. Useful load: 1,007 lbs. Payload with full fuel (67 gal.): 392 lbs. Performance with full load Maximum Speed: 120 mph Cruise Speed (sl.): 103 mph Rate of climb: 720 ft. per minute Surface ceiling: 13,000 ft. Landing speed: 48 mph. Normal cruising range: 650 miles Fuel capacity: 67 gal. Oil capacity: 6 gal. METEOROLOGICAL INFORMATION A weather observation station was located at the United States Air Force Academy Airfield (AFF) about 11 miles south-southeast of the accident site at an elevation of about 6,550 ft. At 0758, AFF reported wind from 250° at 11 knots with gusts to 27 knots, visibility of 10 statute miles or greater, sky clear, temperature of 13°C, dew point temperature of -9°C, and altimeter setting of 29.86 inches of mercury. The remarks section of the observation included peak wind of 33 knots from 220° at 0720. At 0848, AFF reported a wind from 270° at 33 knots with gusts to 48 knots, visibility of 10 statute miles or greater, squall, sky clear, temperature of 12°C, dew point temperature of -8°C, and altimeter setting of 29.84 inches of mercury. An Automated Weather Observing System was located at Kelly Air Park (MNH) about 14 miles northwest-west of the accident site at an elevation of about 7,050 ft. At 0756, MNH reported a calm wind, visibility of 10 statute miles or greater, sky clear, temperature of 7°C, dew point temperature of -6°C, and altimeter setting of 29.91 inches of mercury. An area forecast that included Colorado was issued at 0445. The portion of the area forecast that covered the accident area called for wind gusts of 40 knots from the west-northwest about the time of the accident. WRECKAGE AND IMPACT INFORMATION The airplane came to rest on the crest of an embankment near a set of railroad tracks. A debris field was on a bearing of 110° where small articles and a postimpact fire had spread from the impact crater. The main wreckage came to rest in its impact crater. The propeller was partially driven into the ground with the engine angled and the fuselage lying on the ground. The postimpact fire had consumed nearly all the airplane's fabric and wooden wing spars. Multiple pools of material consistent with solidified molten aluminum were found throughout the wreckage. The left rudder cable remained attached to the rudder and was traced to an overload break near the aft left rudder pedal. Following the break, the remainder of the broken cable led to the aft left rudder pedal. The right cable remained attached to the rudder and was traced to the right aft rudder pedal. Both rudder cables also rem