ANC17FA009

The pilot's operation of the airplane at an altitude that was too low to allow for recovery from an intentional aerodynamic stall, which resulted in an impact with terrain. Contributing to the accident were the pilot's inability to recognize altitude deviations during slow flight due to the sun glare and the pilot's lack of knowledge of the stall performance characteristics of the airplane modified with vortex generators due to the lack of information from the manufacturer.

The airline transport pilot was conducting a post-maintenance test flight following the installation of vortex generators (VGs) on the airplane's wings and horizontal stabilizers. The GPS track data were consistent with the performance of level turns, slow flight, and stalls. The last 2.5 minutes of the flight exhibited a decelerating, descending profile consistent with performance of a power off stall; during this time, the airplane descended from 1,033 ft above ground level (agl) to 469 ft agl and slowed from 81 knots to 26 knots. At 26 knots, an abrupt loss of control occurred as indicated by a sharp right turn and a rapid descent rate of about 2,000 ft per minute (fpm). During the 30 seconds before the rapid descent began, the airplane had a rate of descent of about 500 fpm. The last valid GPS data point showed an increasing groundspeed of 35 knots and an altitude of 75 ft agl. Examination of the accident site indicated that the airplane impacted trees and traveled about 350 ft before coming to rest upright. Examination of the wreckage did not reveal evidence of any preimpact mechanical malfunctions or anomalies that would have precluded normal operation. The GPS data and site examination indicated that the pilot likely lost control of the airplane while performing a full flap aerodynamic stall and was recovering from the maneuver when the airplane impacted trees. According to the GPS data, the pilot initiated the practice stall sequence about 500 ft below the FAA-recommended minimum practice stall recovery altitude of 1,500 ft agl. As a result, the pilot had insufficient altitude to safely recover from the maneuver before the airplane impacted terrain. According to the manufacturer of the VGs, the airplane's expected full flap stall speed was about 33 knots, which was 7 knots higher than the speed at which the loss of control event occurred. Based on the GPS data, the airplane reached 33 knots about 30 seconds before the loss of control and likely entered a stalled condition at that time; however, the pilot apparently failed to recognize the stall and allowed the descent to continue. It is possible that the improved aileron authority at slow airspeeds, which the VG installation provided, allowed the pilot to maintain aileron control while the airplane was in a stalled condition.  Further, according to the manufacturer's test data, the pre-modified airplane would have had a pronounced wing drop at the onset of stall. The stall characteristics of the modified airplane likely contributed to the pilot's failure to recognize that the airplane was stalled. The supplemental type certificate (STC) for the VGs directed the installer to determine compatibility with other STCs, and the installation manual for the VGs stated that STC compatibility may be accomplished by a flight test consisting of a "subjective evaluation of aircraft handling to determine that no adverse characteristics exist." The pilot was conducting this flight test flight when the accident occurred. However, there was no guidance in the installation manual on what characteristics a pilot should expect from a modified airplane or how to conduct such a compatibility test. If such guidance had been available, the pilot may have selected an appropriate altitude for the test and may have recognized and recovered from the stall before losing excessive altitude. The sun's azimuth at the time of the accident was 134° magnetic and slightly above the horizon. The final track of the airplane started at 133° and varied from 111° to 136°, which indicated that the pilot was looking into the sun during the final leg of the flight. The snow-covered ground would have reflected more sun rays into the pilot's eyes, which may have increased the effects of sun glare. It is likely that sun glare impaired the pilot's ability to see the flight instruments and the terrain.

On December 7, 2016, about 1043 Alaska standard time, a tailwheel, ski-equipped Bellanca Citabria 7GCBC airplane, N88452, was substantially damaged when it impacted terrain about 17 miles southeast of Fairbanks, Alaska. The airline transport pilot was fatally injured. The airplane was registered to and operated by the pilot as a Title 14 Code of Federal Regulations Part 91 visual flight rules (VFR) personal flight. Visual meteorological conditions prevailed at the time of the accident, and a VFR flight plan was filed and activated. The local area flight departed Chena Marina Airport (AK28), Fairbanks, at 1026. According to the Federal Aviation Administration (FAA) Fairbanks Flight Service Station records, the pilot filed a local flight plan for a 3-hour flight within a 50-mile area to the east, south and west of Fairbanks International Airport (FAI). The mechanic who had recently worked on the airplane stated that the purpose of the flight was to test the airplane's flight performance following the installation of vortex generators (VGs) on the wings and horizontal stabilizer. The airplane's engine ran rough after the first start, so the mechanic brought the airplane back into the hangar to warm up. He checked the fuel sumps for debris and found none. After warming, the airplane was pushed outside and operated normally after the second start. A review of archived FAA radio communication recordings revealed that the pilot called the FAI air traffic control tower before departure and was provided the current wind of 350° at 5 knots and the altimeter setting of 30.64 inches of mercury. After departure, he requested that his VFR flight plan be activated. The last transmission from the pilot was at 1033 when he asked the FAI tower if the restricted airspace R-2211 was "hot"; the tower reported it was "cold." A Garmin GPSMAP 296 portable GPS receiver was recovered from the wreckage and downloaded at the National Transportation Safety Board (NTSB) Vehicle Recorder Laboratory. The recorded data included time, location, and GPS altitude, as well as derived groundspeed and track information. The airplane began its takeoff roll at Chena Marina Airport at 1026:14, climbed toward the southeast to a GPS altitude of 1,762 ft, and proceeded south over the Tanana Flats. Between 1033:11 and 1037:07, the airplane performed one right 360° turn and two 420° turns (one to the left and one to the right) while flying between GPS altitudes of 1,601 ft and 1,437 ft and maintaining groundspeeds of 44 to 100 knots. At 1037:07, the airplane turned to a southwesterly track of 194° to 201° for about 3 minutes and performed slow flight maneuvers. During this period, the airplane slowed to 46 knots for a period of 19 seconds, accelerated, and then slowed to 40 knots for 14 seconds before accelerating to 68 knots; these changes in airspeed were consistent with the pilot practicing stalls. At 1040:52, the airplane began a southeast track of 133° that lasted for 2 minutes 36 seconds. During this final track, the airplane descended from 1,545 ft to 981 ft, decelerated from 81 knots to 26 knots, and then entered a rapid descent at a rate of about 2,000 ft per minute (fpm) and a rapid turn to the south. About 30 seconds before the rapid descent began, the airplane had a rate of descent of 510 fpm as it decelerated below 40 knots. The last valid GPS data point indicated an increasing groundspeed of 35 knots, an altitude of 587 ft (75 ft above ground level), and a track of 144°. According to FAA air traffic control recordings and documentation, at 1318, about 2.5 hours after the last GPS data point, two US Army CH-47F helicopter crews were flying through the area and located the airplane wreckage after hearing an emergency locator transmitter signal. PERSONNEL INFORMATION The pilot, age 74, held an airline transport pilot certificate with an airplane multi-engine land rating. Additionally, he held commercial privileges for airplane single-engine land and single-engine sea. He held a third-class medical certificate issued on January 22, 2016, with the limitation: must have available glasses for near vision. According to documentation provided by family members, the pilot was well rested and in good health the morning of the accident. The pilot co-owned the airplane with his son. The pilot also owned a Cessna 180 and had been flying it at least monthly according to his logbook entries. Examination of the pilot's logbook revealed that he had recorded about 3,171 hours of flight experience, of which 2,736 hours were in single-engine airplanes and 206 hours were in a Citabria 7GCBC. The pilot's most recent flight review was conducted on February 24, 2016, in his Cessna 180 airplane. The flight instructor who conducted the last flight review stated that he was not sure if stalls were performed during the most recent flight review, but he recalled performing stalls during other reviews with the pilot. He also stated that the pilot was a very competent and conservative pilot. AIRCRAFT INFORMATION The two-seat, high-wing, conventional-gear airplane was manufactured in 1974 and equipped with a 150-horsepower Lycoming O-320-A2D reciprocating engine and a fixed-pitch, two-bladed McCauley metal propeller. The airplane had been altered by the installation of metal wing spars in accordance with FAA Supplemental Type Certificate (STC) SA3829NM. During the week before the accident, the airplane was equipped with Landis L-2000A straight skis in accordance with FAA STC SA261AL and Micro Aerodynamics vortex generators in accordance with FAA STC SA00795SE. The optional stall warning horn was not installed. A review of the maintenance logbooks revealed that the last annual inspection of the airplane was completed on April 4, 2016, at which time the airframe and engine total times were 2,882.24 hours, and the engine time since major overhaul was 875.24 hours. According to the mechanic who maintained the airplane and the logbook entries, the engine throttle cable was removed and replaced the week before the accident due to a stiff throttle. The alternator was removed and replaced the day before the accident due to electrical issues that the airplane had on December 2. The transponder was removed for maintenance before the flight. At the time of the accident, the tachometer indicated 2,889.34 hours and the recording hour meter indicated 1,229.0 hours. Weight and Balance The actual gross weight of the airplane at the time of the accident could not be determined as the fuel quantity could not be verified. According to the mechanic's recollection, the fuel tanks were about 3/4 full before engine start, which would have been about 27 gallons. The airplane's weight and balance condition at the time of takeoff was calculated based on the estimated fuel onboard (156 lbs), the estimated pilot weight based on his most recent medical application and winter clothing (215 lbs + 4 lbs), actual cargo weights (1 lb front seat + 2.5 lb rear seat + 94 lbs in rear baggage area), and the airplane weight and balance form for the Landis ski configuration (1218 lbs empty weight + 15 lbs oil). Page 1-3 of the Bellanca Citabria Pilot Operation Manual (POM) lists the maximum allowable gross weight of 1,650 lbs and the center of gravity limits between 14.2 inches and 19.2 inches aft of datum. The calculated takeoff weight was 1,705 lbs, which was 55 lbs above the maximum allowable gross weight. The airplane's weight at the time of the accident, about 18 minutes later with an estimated 24 gallons of fuel remaining, was calculated at 1,687 lbs. The center of gravity at the time of the accident was calculated using figures 5-1, 5-2 and 5-5 from the Citabria POM and determined to be 17.18 inches. METEOROLOGICAL INFORMATION The closest weather reporting facility to the accident site was at FAI, which was located about 16 miles north of the accident site at an elevation