N2069B

HISTORY OF FLIGHTOn November 18, 2022, at 1019 Pacific standard time, a Textron Aviation 208B, N2069B, was substantially damaged when it was involved in an accident near Snohomish, Washington. The two airline transport pilots and two flight test crewmembers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight.

The operator, Raisbeck Engineering, held the STC for an aerodynamic drag reduction system (DRS) on the Cessna 208B. The accident flight was part of the testing for Raisbeck to expand the applicability of that DRS to the Cessna 208B EX model modified with the Aircraft Payload Extender (APE III) STC, developed by AeroAcoustics Aircraft Systems Inc. QuickSilver Aero was contracted to provide instrumentation support for Raisbeck’s flight test program. At the time of the accident, the Raisbeck DRS STC was not installed.

The airplane began flights to support the flight test three days before the accident. The three flights on the first day comprised a total of 1.1 hours and included a pilot familiarity flight and a ferry flight to have the airplane’s weight and balance measured. Two days before the accident, the flight test data collection flights began. Those included two flights, totaling 4.6 hours, to gather baseline data for both mid center-of-gravity (CG) cruise flight and forward CG stall speeds. The day before the accident, two test flights were performed with the accident test pilot and the accident aft-seated testing personnel. The purpose of the first flight, totaling 1.2 hours, was to test aft CG static stability. The last flight that day, totaling 1.4 hours, was terminated prematurely with only about half of the test plan (card) completed, because an aft crewmember was feeling airsick.

The purpose of the accident flight was to complete the test card from the previous day, which consisted of baseline testing of the aft CG stall characteristics of the airplane modified with the APE III STC. A review of ADS-B and radar track data revealed that the airplane departed Renton, Washington, around 0925, and continued to the north in a gradual climb to about 9,500 ft mean sea level (msl) and began a series of turns/maneuvers. The airplane proceeded for about 45 minutes, its altitude varying between about 6,500 ft to 10,275 ft msl.

The combination of ADS-B and winds aloft information indicated that, at 1017:00, the airplane was in a nearly level, 10° left-banked turn at 10,000 ft msl and about 110 knots calibrated airspeed (KCAS). Around 1017:20, the airplane climbed about 100 ft while slowing to between 90 and 105 KCAS. Shortly thereafter, a gradual left roll increased to 30° and the altitude began steadily decreasing at a rate of about 400 ft per minute (fpm), with the airplane descending from 9,700 ft to 9,350 ft msl by 1018:46. The airspeed remained constant at approximately 105 KCAS between 1018:20 and 1018:44. Engine torque was consistent about 930 ft-lb between 1016:50 and 1019:05. At 1018:43, the computed airspeed dropped rapidly, reaching a minimum of 48 KCAS at 1019:01 before sharply increasing. Engine torque also abruptly increased, reaching 2,200 ft-lb at 1019:20.

Indicated airspeed recorded by the Pratt & Whitney engine monitoring system (FAST) measured 35 knots indicated airspeed (KIAS) at 1019:00 and 37 KIAS at 1019:03 before quickly rising to a maximum of 223 KIAS at 1019:21, then dropping to approximately 80 KIAS as the airplane descended. During this period, the altitude increased from 9,320 ft to 9,680 ft msl between 1018:47 and 1018:59 as airspeed decreased. Vertical speed decreased from +2,560 fpm at 1018:54 to -14,000 fpm at 1019:13. Between 1019:25 and the end of the FAST data at 1019:52, the computed average vertical speed reached about -12,000 fpm.

At 1019:05, the ADS-B data indicated a sudden and tight course reversal from east to west, corresponding with the minimum airspeed and a dramatic increase in the descent rate. The computed roll angle stayed consistent at about 30° left until the course reversal. The ADS-B data stopped at 1019:17 about 7,025 ft msl with a recorded descent rate of 8,700 fpm (see Figure 1 below). The location of the wreckage, witness statements, and video footage were all consistent with the airplane breaking apart inflight shortly thereafter. The main wreckage was located about 2,145 ft east of the last recorded return.

Figure 1: Radar data of maneuvers during flight (left) and last turn (right)

Witnesses reported that they observed the airplane break up in flight and watched pieces floating down. The airplane then descended in a nose-low, near-vertical corkscrew maneuver toward the ground. Several witnesses reported seeing a white plume of smoke when they observed the airplane break into pieces. A security camera recorded a low-quality image of the airplane rotating about its longitudinal axis in nose-low attitude (see figure 2 below).

Figure 2: Picture from witness (left) and excerpts of video still images (right)

The airplane’s flight test data acquisition system, used as part of the flight test program, was destroyed in the accident and no flight test data for the accident flight was recovered.

The right seat pilot who flew the test flights the day before the accident reviewed the track data for the accident flight. He believed that just before the accident, the crew were likely performing second-to-last maneuver on the card, which specified: airspeed 96 KIAS; flaps in landing configuration; 930 ft-lbs of torque; propeller rpm fully forward; and accelerated 30° bank to the left.

The airplane's maneuvers and speeds leading up to the minimum airspeed recorded at 1019:01 suggests the performance of an intentional stall in a 30° left roll with the engine power above idle (at about 930 ft-lb of torque), consistent with the stated intent of the flight and the items remaining on the flight test card for that flight (including a power-on stall in a 30° bank). PERSONNEL INFORMATIONThe test pilot was seated in the front left seat. He was contracted by Raisbeck through the company’s Organization Designation Authorization program, which allows Raisbeck to perform specific functions on the FAA’s behalf. On August 1, 2022, he completed the FAA recurrent training for a Designated Engineering Representative/Flight Test Designee.

The pilot's personal flight records were not recovered, but information provided to the insurance company before the accident indicated 11,720 total hours of flight experience, of which 232 hours were in the accident airplane make and model.

The right seat pilot had accrued 10,900 total hours of flight experience, of which 5,000 hours were in the accident airplane make and model. AIRCRAFT INFORMATIONThe Textron Aviation (formerly Cessna) 208B EX Grand Caravan is a single-engine, propeller-driven, single-pilot airplane originally designed as the 208 for the first production model certified in 1984. The 208B incorporates a fuselage extended by 4 feet and was certified as an 11-seat passenger airplane in 1989. The high-wing airplane is equipped with wing struts, a conventional tail, fixed tricycle landing gear, and an underbelly cargo pod. The airplane is powered by a single Pratt & Whitney Canada PT6A-140 turboprop engine driving a McCauley 4-blade, constant speed, full feathering, reversible pitch propeller. The airplane is certificated in the normal category, which includes maneuvers incidental to normal flying such as stalls (except whip stalls), lazy eights, chandelles, and turns with bank angles not more than 60°. Aerobatic maneuvers, including spins, are not approved.

On November 1, 2022, AeroAcoustics Aircraft Systems STC SA01213SE, Aircraft Payload Extender (APE) III, was installed on the airplane. The STC adds wing stall fences to both wings outboard of the landing lights, new main landing gear axles, and 29-inch main landing gear tires to increase the maximum takeoff and landing weights and increases the payload and range.

On November 11, 2022, AeroAcoustics Aircraft Systems STC SA01805SE, Aircraft Payload Extender STOL, was installed on the airplane. The STC installs a scalloped Gurney flap on the trailing edge of each flap to improve the low-speed aerodynamics of the wing.

On November 14, 2022, the FAA issued a Special Airworthiness Certificate in the Experimental category for the purpose of research and development for the airplane. The certificate was requested by Raisbeck Engineering to perform company flight testing for the development of an STC for the airplane.

The installed STCs on the airplane imposed limitations beyond those published in the Pilot’s Operating Handbook (POH):

Limit Speeds (IAS): Maneuvering Speed at 9,062 lbs = 143 kt

Maximum Weights: Takeoff: 9,062 lbs

Limit Factor: Flaps up: +3.36, -1.34

Limits (g’s): Flaps down (all settings): +2.00

Max Operating Speed (Vmo): 175 KIAS

Maneuvering Speed (VA): 148 KIAS (at 8,807 lbs)

Max Flap Extended Speed (Vfe): 125 KIAS (Land) ; 150 KIAS (Takeoff)

Flap Operating Range: 50-125 KIAS

The airplane’s approximate weight at the time of the accident was 7,965 lbs with the CG at 203.5 inches. The airplane’s aft CG limit is 204.35 inches aft of datum at all weights up to 8,807 lbs. The datum is located 100 inches forward of the face of the firewall.

The airplane was equipped with a Garmin G1000NXi integrated glass cockpit. Included is an electronic flight instrument system (EFIS) composed of 2 primary flight displays (PFDs) and a multi-function display (MFD). Incorporated is the GFC 700 Automatic Flight Control System (AFCS), a fully digital, three-axis, dual channel, fail passive autopilot.

The airplane was also equipped with an Electronic Stability and Protection (ESP) system, which operates through the air data computers, the attitude and heading reference system (AHRS), and autopilot servos in the integrated avionic systems independently of the autopilot. According to th...