NTSB Factual Report

On February 19, 2017, about 1215 eastern standard time, an Ercoupe 415-C, N99716, was substantially damaged during a precautionary landing to a road near Dawsonville, Georgia. The private pilot sustained minor injuries. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed for the personal flight that was operated under the provisions of 14 Code of Federal Regulations Part 91. The flight departed from Jackson County Airport (JCA), Jefferson, Georgia, about 1100, with the intended destination of Barwick LaFayette Airport (9A5), LaFayette, Georgia.

According to the pilot, he had recently purchased the airplane and was flying it back to his home airport. In the day and a half prior to the accident flight, the pilot cleaned oil from underneath the airplane three separate times. When he examined the engine to determine where the oil was leaking from, he only noted oil coming from the crankcase breather tube. In addition, on the afternoon prior to the accident, he checked the oil level after a morning flight and noted the oil level was down "7 ounces" from 3.5 quarts.

Then, prior to the accident flight, he added 1/2 quart of oil to bring the oil level up between 3.5 and 4 quarts. About 30 minutes after he departed, the pilot noticed the oil pressure was dropping. He reduced engine power and turned the airplane toward Lee Gilmer Memorial Airport (GVL), Gainesville, Georgia. He watched the oil pressure continue to decrease and decided to perform a precautionary landing on a road. During the landing, the left main landing gear and nose landing gear contacted a grass area to the left of the road. The airplane skidded across the road until it impacted a tree and came to rest in a ditch. The pilot then egressed from the airplane with minor injuries.

During an interview with a Federal Aviation Administration (FAA) inspector, the pilot stated that the oil pressure never went to zero and the engine was not running erratically when he made the decision to reduce engine power and perform a precautionary landing. The only indication of an issue was the loss of oil pressure and that there were no issues with oil temperature.

According to FAA records, the airplane was manufactured in 1955 and was powered by a Continental Motors C75 series, 75-horsepower engine. According to airplane maintenance logbooks, an annual inspection was performed on September 4, 2016, at a total time in service of 1,880 hours. In addition, the most recent recorded oil change occurred at that time and the oil screen was cleaned with no metallic debris noted. According to the engine manufacturer, the maximum engine oil sump capacity was 4.5 quarts. In addition, the minimum idling oil pressure was 10 psi and the oil pressure at cruise was between 30 psi and 35 psi.

Examination of the airplane by an FAA inspector revealed that both wings sustained substantial damage and fuel was noted leaking from the wings. Examination of the engine revealed a hole in the oil sump consistent with impact damage, and oil was noted coming from the crankcase breather tube. In addition, oil was noted on the bottom of the airplane from the nose to the empennage.

Additional examination of the engine was performed at a salvage facility in Griffin, Georgia, under the supervision of an FAA inspector. The oil level was noted at 3.5 quarts before the engine run. The engine was started with no hesitation and was able to maintain an oil pressure of 45 psi. The engine was operated for about 10 minutes at various power settings. To duplicate the loss of oil pressure, 1 quart of oil was added to the engine, bringing the level up to 4.5 quarts, and it was restarted. The engine operated, the oil pressure was noted as 45 psi, however, after about 5 minutes, the oil pressure began to decrease slowly. The oil pressure settled at 25 psi for a few seconds, then gradually increased back to 45 psi, and remained there until the engine was shutdown.

According to an academic paper written by an engineer at Massachusetts Institute of Technology titled "Engine Lubrication Oil Aeration," it stated that "if the oil level is too high there is a possibility of interaction between the sump oil and the rotating crankshaft that can cause air bubbles to become entrained in the oil and increase the aeration level."

NTSB Probable Cause

A decrease in oil pressure due to the pilot's unintentional overfilling of the engine oil sump, and the pilot's subsequent decision to perform an off-airport precautionary landing, which resulted in impact with a tree.