On October 28, 2018, at 1830 eastern daylight time, a Diamond DA-20, N653DC, was substantially damaged during collision with terrain during a forced landing in Mountain Rest, South Carolina. The forced landing followed a loss of engine power while in cruise flight about 6,500 feet mean sea level (msl). The pilot and his passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight which was conducted under the provisions of 14 Code of Federal Regulations Part 91.According to the pilot, the airplane was in cruise flight approximately 6,500 feet msl when the engine experienced a partial loss of engine power. The engine speed slowed to 1,000 rpm and the pilot adjusted the flight controls to achieve the airplane's best glide performance.
The pilot stated that he selected a field for the forced landing because no airport was within gliding distance. During the descent, the pilot's remedial actions to restore engine power were unsuccessful, so he declared an emergency over the radio and secured the engine prior to the off-airport landing. After the landing, the occupants egressed the airplane uninjured and without assistance.
The pilot held a commercial pilot and flight instructor certificates with ratings for airplane single engine land, multiengine land, and instrument airplane. His Federal Aviation Administration (FAA) first class medical certificate was issued February 1, 2018, and he reported 1,477 total hours of flight experience.
According to FAA records, the airplane was manufactured in 2001. Its most recent 100-hour inspection was completed October 24, 2018 at 7,730 total aircraft hours.
At 1835, the weather recorded at Toccoa Letourneau Airport (TOC), 18 miles southwest of the site, included clear skies and winds from 240 degrees at 6 knots. The temperature was 19°C, and the dew point was 10°C. The altimeter setting was 29.94 inches of mercury.
Examination of photographs revealed that the wings, fuselage, and empennage all sustained substantial impact damage. The tail was fractured but remained attached by cables. The horizontal stabilizer and the elevator were separated from the tail section.
An FAA aviation safety inspector confirmed flight continuity from the cockpit, through breaks and fractures, to all flight control surfaces. All breaks and fractures exhibited signatures consistent with overload failure. Several gallons of fuel were drained from the airplane, and samples from the fuel were absent of water and debris.
The airplane was retained for further examination.
On November 27, 2018, an engine run was attempted using an external battery and the airplane's own fuel system. Several starts were attempted, but each was unsuccessful. The testing was suspended, and the engine was removed and shipped to the manufacturer for further testing.
On December 4, 2018, the engine was examined in Mobile, Alabama. Ignition timing on the right magneto could not be verified. Timing was initially confirmed on the left magneto. The engine was placed in a test cell, and a start was attempted. The engine ran roughly and would not run continuously. Troubleshooting was performed, and internal engine timing and ignition timing were confirmed. Ultimately, both magnetos and both ignition harnesses required replacement to achieve a successful engine run.
The right magneto was tested using a magneto synchronizer, which revealed the points would not close, and the magneto would not produce spark. The right magneto was disassembled, and examination revealed the distributor gear bushing showed extreme wear. Debris (dust) consistent with the bushing material and the distributor gear block coated the internal magneto components. The distributor gear and distributor drive gear were loose in their mounts. The distributor gear block displayed excessive wear on the bushing, the bushing race, and the clearance cut-out adjacent to the drive gear.
The left magneto timing was verified on the engine, but then would not function in the test cell. The magneto was removed, the points were cleaned, the magneto was then bench tested again and functioned as designed.
The ignition harnesses were bench tested. The right-side harness showed continuity through all terminal leads, but the high-energy spark "leaked" through damaged areas in the #2 and #4 leads. The damage was consistent with over-tightening at the terminal harness b-nuts and clamp sites, as well as chafing at the clamp sites. Some impact-related damage was also noted.
The left-side harness showed continuity through all terminal leads. The high-energy spark "leaked" through damaged areas throughout. The damage was consistent with that of the right-side harness.