History of Flight
On April 24, 2016, at 1706 Pacific daylight time, a DG Flugzeugbau GmbH DG-800B motorglider (registration N800YG) struck trees during a landing near Clements, California. The private pilot, who was the sole occupant and operator, was not injured. The glider sustained substantial damage. The cross-country personal flight had departed Byron Airport, Byron, California, at 1417 under visual meteorological conditions. No flight plan was filed.
The pilot used a tow-plane for departure. About 2 1/2 hours into the flight, while returning to Byron, the glider encountered reduced lift and descended to about 2,400 ft above ground level (agl). Unable to maintain altitude, the pilot selected a field for landing about 5 miles away. He intended to perform an engine air-start before touchdown and then return to Byron under powered flight. If the engine did not start, he would proceed with the landing.
The pilot overflew the field while descending from 1,700 to 1,100 ft agl. During the downwind leg, he configured the glider for landing and extended the retractable propeller mast. He could not get the engine to start on the first attempt, which he reported was not unusual, so he made two more attempts. Each time, the engine rotated and "cough[ed]" as the starter engaged but did not continue under its own power.
Having descended to 500 ft agl, with insufficient time to retract the propeller mast, the pilot initiated a base turn for landing. During the turn, he realized wind conditions were stronger than anticipated and he would not reach the intended landing spot. Without a safe alternate, he continued the approach, landing short into a group of eucalyptus trees.
The glider came to rest left wing down, with the cabin about 10 ft above ground against a tree trunk. The pilot secured the glider, opened the canopy, and climbed down. The left wing fragmented during the accident sequence, and the tailboom twisted away from the main cabin along the longitudinal axis.
Glider Information
The composite glider was manufactured by DG-Flugzeugbau GmbH in Germany in 1998 and exported to the United States that year. At the time of the accident, it was registered in the experimental/exhibition category. It was equipped with a 53-horsepower SOLO 2625-01 two-stroke engine and a two-blade composite propeller. The engine and propeller were attached to an electrically-driven pivoting mast assembly behind the cabin, which could be extended and retracted automatically or manually.
The most recent condition inspection was completed on April 3, 2016. At that time, the airframe had accumulated 2,062.7 total flight hours, and the engine 98.5 hours. Maintenance logbooks indicated that at the prior inspection in July 2014, the airframe total time was 2,048.6 hours and engine time 97.6 hours.
The pilot reported that the engine was last operated on October 17, 2015, as an in-flight start. In November 2015, he "winterized" the engine in accordance with the engine's operation manual by injecting two-stroke oil into the carburetor, cranking the engine ten turns by hand, and covering the carburetor intake and exhaust muffler outlet. The manual recommended draining the fuel tank for inactivity over 60 days, but the pilot did not drain it; instead, he topped it off with a 50:1 premix of 100 low-lead aviation fuel and two-stroke oil.
The engine was not started during the annual inspection 21 days before the accident, but the pilot rotated it by hand, confirming smooth operation.
Examination and Testing
The airframe and engine were examined by the NTSB investigator-in-charge after recovery. The examination revealed no mechanical malfunctions or failures that would have precluded normal operation. The fuel tank contained 6 liters of fuel (maximum capacity 22 liters, unusable 0.5 liters). The engine and propeller mast assembly were extended per flight manual instructions, and the engine started on the third attempt. Multiple subsequent engine starts and runs were performed successfully at varying speeds.
Pilot Comments
The pilot reported no mechanical malfunctions or failures with the glider or engine. He noted that self-launching gliders are prone to starting difficulties, especially after a period of non-use, and that he should not have relied upon the engine to prevent an outlanding. He acknowledged that the accident resulted from a series of events: a lack of flight currency (his last flight was in October 2015), his decision to start the flight late in the day and attempt a return in deteriorating conditions, his failure to initiate the engine restart at a higher altitude, his omission to run the engine prior to the accident flight after an extended period of non-use, and spending too much time and attention on engine start and not enough on landing.
Flight Manual Guidance
The glider's flight manual warnings state: "With a motorglider never rely completely on the engine extending and starting. Plan your flight path so that you are always able to carry out a safe outlanding if necessary. Be aware that with the engine extended but not running the rate of sink increases remarkably." The normal procedures section notes that with the engine extended but not running, the rate of sink at 49 kts increases to 395 ft/min, and recommends restarting the engine only over landable terrain and not below 1,320 ft agl, but states it is better to restart at 660 ft over a landable field than at 1,320 ft over unlandable terrain.