Pilot Debrief

BELLANCA 7GCBC near Fairbanks, AK — 2016-12-07

Final reportANC17FA009
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Date
2016-12-07
Location
Fairbanks, AK, USA
Aircraft
BELLANCA 7GCBC
Registration
N88452
Category
Airplane
Highest injury
Fatal
Fatalities
1
Phase of flight
Maneuvering

Probable cause

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.

Contributing factors

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.

NTSB narrative

**This report was modified on August 6, 2026. Please see the public docket for this accident to view the original report.** The airline transport pilot was conducting a post-maintenance test flight on the ski-equipped airplane 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 1,092 ft above ground level (agl) to 510 ft agl and slowed from a ground speed of 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 3,940 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 ground speed of 35 knots and an altitude about 114 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—the practice sequence for which was initiated about 500 ft below the FAA-recommended minimum altitude of 1,500 ft agl—and was attempting recovery from the maneuver when the airplane impacted trees. The Bellanca 7GCBC Pilot Operating Manual (POM) states the airplane’s stall speed is 45 mph, or 39 knots, in a full flaps configuration, assuming the airplane is operating at its maximum gross weight, idle power, and 1 g level flight. According to the manufacturer of the VGs, application of the supplemental type certificate (STC) to the airplane would have reduced its published stall speed by about 8 percent, which would correspond to a calibrated airspeed (CAS) of 36 knots. Although the accident airplane’s airspeeds were not recorded, reported surface winds near the accident site were between 1 and 5 knots; therefore, the airplane’s GPS ground speed likely approximated its airspeed. Based on the GPS data, the airplane reached an estimated CAS of 36 knots about 1043:00 AST while descending at a rate of 500 fpm through about 750 ft agl. Over the next 22 seconds, the airplane’s airspeed and altitude decayed further to 26 knots and 510 ft agl (1,018 ft above mean sea level, or 981 ft GPS [geometric] altitude). Analysis of the GPS data indicate that the stall and loss of control occurred concurrently at 1043:28, at which time the airplane entered a right bank of 24° and its descent rate increased to 3,940 fpm. The STC for the VGs directs installers to determine compatibility with other STCs, and the installation manual for the VGs states 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 when the accident occurred. However, evidence suggests that the flight test was conducted only to evaluate the VG installation rather than its compatibility with the skis installed on the airplane that were also an STC modification. Among other considerations, because the effects of the newly installed VGs on the airplane’s stall characteristics had not been established by the pilot, and because the effects of the airplane’s combined ski and VG configuration were likewise unknown, the flight test warranted selecting an altitude for a power-off stall that provided additional margin for unexpected stall behavior. The Australia Civil Aviation Safety Authority issued an airworthiness bulletin about 5 months before the accident advising operators and maintenance personnel about potential unsafe conditions, including loss of control, as a result of “unfavorable interaction between combinations of aerodynamic performance enhancing STCs.” The FAA-recommended altitude for practice stalls is intended as a minimum to allow sufficient altitude for recovery. Given that the accident flight appeared to be the pilot’s first with both modifications, the decision to initiate the power-off stall below the FAA-recommended minimum altitude reflected inadequate risk management and did not provide sufficient margin for recovery. Although the VG installation manual recommended a post-installation flight test to evaluate airplane handling, it contained no guidance on the characteristics a pilot should expect from a modified airplane or how to conduct such a test. If such guidance had been available, the pilot may have selected an appropriate altitude for the stall practice sequence and may have recognized the airplane was in a stalled condition before losing too much altitude to successfully recover.

Analysis

Primary failure mode
Loss of control
First missed decision gate
Pilot could have avoided practicing stalls at low altitude.

NTSB coding

Evidence available

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  • 11 docket documents
View NTSB final reportView NTSB docket

Docket documents11

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