Accident Overview
On February 19, 2017, about 1215 eastern standard time, an Ercoupe 415-C, registration 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, which was operated under 14 Code of Federal Regulations Part 91. The flight originated from Jackson County Airport (JCA), Jefferson, Georgia, about 1100, with an intended destination of Barwick LaFayette Airport (9A5), LaFayette, Georgia.
Pilot's Account
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, he cleaned oil from underneath the airplane three times. When he examined the engine to find the oil leak source, he only noted oil coming from the crankcase breather tube. On the afternoon before the accident, he checked the oil level after a morning flight and found it down 7 ounces from 3.5 quarts. Before the accident flight, he added 1/2 quart of oil to bring the level between 3.5 and 4 quarts.
About 30 minutes after departure, the pilot noticed the oil pressure dropping. He reduced engine power and turned toward Lee Gilmer Memorial Airport (GVL), Gainesville, Georgia. As oil pressure continued to decrease, he decided to land 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, struck a tree, and came to rest in a ditch. The pilot egressed with minor injuries.
During an interview with a Federal Aviation Administration (FAA) inspector, the pilot stated that the oil pressure never reached zero and the engine was not running erratically when he reduced power. The only indication of an issue was the loss of oil pressure; oil temperature was normal.
Aircraft and Maintenance Information
According to FAA records, the airplane was manufactured in 1955 and powered by a Continental Motors C75 series, 75-horsepower engine. Airplane maintenance logbooks indicated an annual inspection on September 4, 2016, at a total time in service of 1,880 hours. The most recent recorded oil change occurred at that time, and the oil screen was cleaned with no metallic debris found. The engine manufacturer specifies a maximum oil sump capacity of 4.5 quarts, minimum idling oil pressure of 10 psi, and cruise oil pressure between 30 and 35 psi.
Post-Accident Examination
FAA inspection revealed substantial damage to both wings and fuel leaking from the wings. Examination of the engine showed a hole in the oil sump consistent with impact damage, and oil was observed coming from the crankcase breather tube. Oil was noted on the bottom of the airplane from nose to empennage.
Further examination at a salvage facility in Griffin, Georgia, under FAA supervision, involved adding oil to the engine. The oil level was initially 3.5 quarts. The engine started without hesitation and maintained oil pressure of 45 psi. It was operated for about 10 minutes at various power settings. Then, 1 quart of oil was added to bring the level to 4.5 quarts. After restart, oil pressure remained at 45 psi for about 5 minutes, then decreased slowly to 25 psi for a few seconds before gradually increasing back to 45 psi, where it remained until shutdown.
Relevant Research
An academic paper from Massachusetts Institute of Technology titled "Engine Lubrication Oil Aeration" states that if the oil level is too high, there is a possibility of interaction between the sump oil and the rotating crankshaft, which can cause air bubbles to become entrained in the oil and increase aeration levels.