Accident Overview
On October 28, 2018, at 1830 eastern daylight time, a Diamond DA-20, registration N653DC, was substantially damaged during a forced landing in Mountain Rest, South Carolina. The forced landing followed a partial loss of engine power while the airplane was in cruise flight at approximately 6,500 feet mean sea level (msl). The pilot and passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91.
Pilot and Aircraft Information
The pilot held commercial pilot and flight instructor certificates with ratings for airplane single-engine land, multiengine land, and instrument airplane. His FAA first-class medical certificate was issued on February 1, 2018, and he reported 1,477 total hours of flight experience.
The airplane was manufactured in 2001 and had its most recent 100-hour inspection on October 24, 2018, at 7,730 total aircraft hours.
Sequence of Events
According to the pilot, while cruising at about 6,500 feet msl, the engine speed dropped to 1,000 rpm. He adjusted the flight controls for best glide performance and selected a field for the forced landing, as no airport was within gliding distance. During the descent, his attempts to restore engine power were unsuccessful. He declared an emergency over the radio and secured the engine before landing. After touchdown, the occupants exited the airplane without assistance.
Weather Conditions
At 1835, weather recorded at Toccoa Letourneau Airport (TOC), 18 miles southwest of the accident site, included clear skies, wind from 240 degrees at 6 knots, temperature 19°C, dew point 10°C, and altimeter setting 29.94 inches of mercury.
Aircraft Damage Examination
Photographs showed that the wings, fuselage, and empennage sustained substantial impact damage. The tail was fractured but remained attached by cables. The horizontal stabilizer and elevator were separated from the tail section. An FAA aviation safety inspector confirmed flight control continuity from the cockpit to all surfaces; all breaks and fractures exhibited overload failure signatures. Several gallons of fuel were drained from the airplane and were absent of water and debris. The aircraft was retained for further examination.
Engine Testing and Examination
On November 27, 2018, an engine run was attempted using an external battery and the airplane's own fuel system. Several start attempts were unsuccessful; testing was suspended, and the engine was removed and shipped to the manufacturer. On December 4, 2018, the engine was examined in Mobile, Alabama. Ignition timing on the right magneto could not be verified; left magneto timing was initially confirmed. The engine ran roughly in a test cell and would not run continuously. Troubleshooting confirmed internal engine and ignition timing. Both magnetos and both ignition harnesses required replacement for a successful engine run.
The right magneto, tested with a magneto synchronizer, revealed that its points would not close and it produced no spark. Disassembly showed extreme wear on the distributor gear bushing. Debris consistent with bushing material and distributor gear block coated internal components. The distributor gear and drive gear were loose, and the distributor gear block exhibited excessive wear on the bushing, bushing race, and clearance cut-out.
The left magneto, after timing verification, failed to function in the test cell. Its points were cleaned, and bench testing showed it functioned as designed.
Ignition harnesses were bench tested. The right-side harness had continuity through all leads, but high-energy spark leaked through damaged areas in the #2 and #4 leads. Damage was consistent with over-tightening at terminal b-nuts and clamp sites, as well as chafing at clamp sites; some impact-related damage was also noted. The left-side harness showed similar leakage through damaged areas from the same causes.