N50FU

HISTORY OF FLIGHTOn August 31, 2023, about 1339 mountain daylight time, a Schleicher Alexander GmbH & Co ASH 26E motor glider, N50FU, was substantially damaged when it was involved in an accident near Wellington, Colorado. The pilot sustained fatal injuries. The glider was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

Flight track data transmitted from an onboard recorder showed the self-launching motor glider departed to the northwest from the Owl Canyon Gliderport (4CO2), Wellington, Colorado, at 1320 (see figure 1).

Figure 1. Flight track data from onboard recorder.

During the climb, the pilot performed several turns, and the glider reached a maximum GPS-derived altitude of about 7,800 ft at 1330. The flight track data showed the glider then entered a steady descent on a northwest track, turned 180°, and flew southwest for about 2 miles before it turned back to the west. The last recorded position at 1339:43 showed the glider on a track of about 296°, with a ground speed of 60 kts and a GPS altitude of 5,948 ft, which was about 250 ft above ground level. PERSONNEL INFORMATIONThe pilot’s flight history and hours of flight experience were obtained from his FAA medical certificate applications and Online Contest (OLC) Glider Logbook because his pilot logbook was not located. The OLC Logbook contained uploaded glider flights since 2007. The pilot’s last equivalent flight review was an annual check required for his Colorado Soaring Association membership. AIRCRAFT INFORMATIONThe Schleicher Alexander GmbH & Co ASH 26E motor glider is self-launching and of composite construction. It is equipped with an engine in the fuselage and a retractable propeller, which is mounted on a pylon that is raised and lowered out of the fuselage behind the cockpit. During normal operation, the propeller pylon is raised electrically to a vertical position before starting the engine. When the pilot is done using the engine to take off or obtain altitude, the propeller is stopped in a vertical position for stowing, and the pylon is then lowered to an engine cool-down position for a short time to allow cooling air to pass through the engine radiator. Once the engine is cool, the propeller pylon is stowed horizontally and faired in the fuselage.

During postaccident examination, the propeller pylon was found in the engine cool-down position, but the propeller was horizontal, and no indication was found that the mechanism that holds the propeller vertical for stowing had been engaged. The manufacturer stated that the position was unusual. Although the manufacturer did not have operational experience with the propeller in this configuration, it presumed the position of the propeller would not have had a significant effect on the flight characteristics of the accident glider, based on its knowledge that the propeller pylon has a marginal effect on the glider’s flight characteristics in either the fully extended or engine cool-down position.

The glider manufacturer estimated that recovery from an aerodynamic stall would result in a minimum altitude loss of 100 to 200 ft.

The glider maintenance logbooks were not located. METEOROLOGICAL INFORMATIONA weather study was conducted using archived weather imagery and data for the accident site and surrounding region. All available weather products showed no significant weather over the area of the accident. The National Weather Service (NWS) issued a soaring forecast at 0655 that indicated excellent conditions for thermal soaring.

The NWS Graphical Turbulence Guidance (GTG) depiction of the maximum expected eddy dissipation rate (EDR) below 18,000 ft at 1400 is shown in figure 2. It forecast EDR values between 16 to 30 over the area, which corresponds to light to moderate turbulence for a light aircraft (less than 15,500 lbs takeoff weight).

There were no NWS inflight weather advisories over the area at the time of the accident for any significant convection, turbulence, icing, low-level wind shear, instrument meteorological conditions, or mountain obscuration.

Figure 2. Graphical Turbulence Guidance for 1400 local time on August 31, 2023.

Mountain wave activity was forecast and observed in the accident area. The sounding wind profile indicated a surface wind from the southwest and transitioning to the west with height, with the mean 0 to 18,000 ft wind from 260° at 20 kts. The sounding vertical wind profile did not indicate any significant vertical wind shears with height over the region. The wind profile did support the development of mountain wave activity with a predominate wave near 14,000 ft.

GOES-18 Low-Level and Mid-Level Tropospheric Water Vapor satellite imagery depicted a transverse banding pattern, with mid-level drying or moisture channel darkening over the region at the time of the accident. The strong brightness temperature variations were consistent with updrafts and downdrafts.

From 1200 through 1600, eight PIREPs were submitted in the accident area. Of these, 7 reported light to moderate turbulence and 1 reported mountain wave activity at 41,000 ft with 500 ft per minute vertical speed deviations. AIRPORT INFORMATIONThe Schleicher Alexander GmbH & Co ASH 26E motor glider is self-launching and of composite construction. It is equipped with an engine in the fuselage and a retractable propeller, which is mounted on a pylon that is raised and lowered out of the fuselage behind the cockpit. During normal operation, the propeller pylon is raised electrically to a vertical position before starting the engine. When the pilot is done using the engine to take off or obtain altitude, the propeller is stopped in a vertical position for stowing, and the pylon is then lowered to an engine cool-down position for a short time to allow cooling air to pass through the engine radiator. Once the engine is cool, the propeller pylon is stowed horizontally and faired in the fuselage.

During postaccident examination, the propeller pylon was found in the engine cool-down position, but the propeller was horizontal, and no indication was found that the mechanism that holds the propeller vertical for stowing had been engaged. The manufacturer stated that the position was unusual. Although the manufacturer did not have operational experience with the propeller in this configuration, it presumed the position of the propeller would not have had a significant effect on the flight characteristics of the accident glider, based on its knowledge that the propeller pylon has a marginal effect on the glider’s flight characteristics in either the fully extended or engine cool-down position.

The glider manufacturer estimated that recovery from an aerodynamic stall would result in a minimum altitude loss of 100 to 200 ft.

The glider maintenance logbooks were not located. WRECKAGE AND IMPACT INFORMATIONThe accident site was in a relatively flat agricultural field about 6 nautical miles northwest of 4CO2. The motor glider impacted the ground about 77° nose-down attitude, on a heading of 213°, about 900 ft north of the last position logged by the onboard flight recorder. The impact site consisted of a small circular depression and two ground scars that extended the length of the wingspan, consistent with the forward fuselage and both wing leading edges. The wreckage was located about 15 ft northeast of the impact site, upright, and oriented with the ground scar.

Postaccident examination of the glider revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Flight control continuity from the control surfaces to the cockpit controls was confirmed. Both flap control surfaces, aileron control surfaces, and the cockpit flap actuator were in the landing position. Both wing airbrake surfaces were in the retracted position. The pilot’s lap belt was unlatched and located underneath the pilot, and the shoulder harness was unlatched and stowed on a fuselage shelf behind the seat.

The propeller and driveshaft were in the cool-down position with no damage observed to the propeller blades. The propeller was perpendicular to the storage position and the propeller stop control was in the non-stop position. The engine throttle control was found in the idle position. The master switch position could not be determined due to impact damage.

The LXNAV Nano 3 flight recorder mounted on the glareshield on a previous flight (see figure 3) was not located. However, its mount and attachment hardware were located in the debris field. Flight track data from the unit was recovered by a soring club.

Figure 3. Cockpit instrument panel photograph uploaded by the pilot on a previous flight.

The LXNAV Variometer, S/N 05708, mounted in the upper center of the instrument panel, was recovered and shipped to the NTSB Vehicle Recorder Laboratory for data download. However, due to data buffering, no additional flight track points could be recovered beyond the last transmitted flight track data point from the LXNAV flight recorder.

Postaccident examination of the engine was unable to be performed due to miscommunication before the glider was salvaged and destroyed at the request of the insurance carrier. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy of the pilot was performed by the Office of the Larimer County Coroner/Medical Examiner. According to the autopsy report, the cause of death was multiple blunt force injuries, and the manner of death was accident.

The pilot’s last aviation medical examination was in 1999. He did not hold a current medical certificate. Medical certification is not required for glider operations. The pilot’s autopsy identified severe coronary artery disease, including 90% narrowing of the left circumflex coronary artery, 70% narrowing of the left anterior descending coronary artery, and 30% narrowing of the right coronary artery by plaque. Borderline left ventricular hypertrophy and hypertensive and diabetic kidney tissue changes were...