Diamond DA20 accident near Matthews, Virginia, June 14, 2021

The NTSB's narrative final · quoted from the NTSB record

Due to an active military operations area, the flight instructor and student pilot on a short cross-country instructional flight to an island were instructed by air traffic control to descend from 5,500 ft mean sea level (msl) to 2,500 ft msl. After the student pilot leveled the airplane at 2,500 ft msl, the engine shook violently and lost all power. The flight instructor took control of the airplane and realized that there was not enough altitude to glide to shore. The flight instructor then ditched the airplane near a fishing trawler where he and the student pilot were rescued. The wreckage was recovered about 2 weeks after the accident and examined at a recovery facility. Examination of the engine revealed that the oil sump drain plug was missing, and the Nos. 1 and 2 connecting rods were fractured in a manner consistent with oil starvation. Review of maintenance records revealed that the airplane’s most recent 100-hour inspection was completed 4 days and 9.3 operating hours before the accident. During an interview, the mechanic who performed the 100-hour inspection stated that he remembered draining the old oil, reinstalling the drain plug with a new gasket, torquing it per the maintenance manual, and securing it with safety wire. He did not remember anything abnormal or any interruptions during the work. Although the mechanic stated that he torqued and safety wired the drain plug, the findings of the investigation the accident suggest that the mechanic likely installed the plug finger-tight and forgot to secure it. Due to normal engine vibration, the plug unscrewed, and the engine oil drained out, which resulted in the total loss of engine power due to oil starvation.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.