The Cessna L19 pilot reported that, during post-flight maintenance, he left the oil filler cap off.
During takeoff, he realized that the oil filler cap was not installed. He noticed a decrease in oil pressure and made a precautionary landing at an airport in Kennett, Missouri.
During landing, the plane landed hard, bounced, and the landing gear collapsed. The airplane skidded off the right side of the runway and ground looped to the right. The left wing hit the ground before the airplane stopped.
The airplane sustained substantial damage.
The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.
Probable Cause: The pilot’s failure to install the engine oil filler cap before the first flight of the day; his subsequent failure to conduct a preflight check before the accident flight, which resulted in his failure to note that the cap was not installed; and his improper landing flare during a precautionary landing, which resulted in a bounced landing and ground loop.
This September 2019 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
I agree with Michael, way more involved here than just loose Oil cap!
I’ve flown L-19 for over 30+ years towing gliders leaving the oil cap off is no big deal, your windscreen will get covered in oil, the oil will go everywhere, And you will have a clean-up job. You don’t total the airplane, in experience, or he panic. I believe that seeing the oil going everywhere, He panic. Someone else one time fueled and check the oil in the L-19 for me, I got in and trusted him that he put the fuel caps back on and the oil cap without checking, That taught me a lesson that I never forget, I got in it and took off. I called him a dum ass and made him clean the airplane. I always check after being re-fueled before starting up.
Does not having the engine oil cap on properly cause a landing hard enough to severely damage an airplane, or did the pilot focus all of his attention on the oil cap and forget his first priority and fly the airplane? Even if the engine seized in flight, the L-19 would still be flying (aka-really crappy glider, but still flying) and should land safely.
Read the NTSB report where the Pilot describes, in order, what happened and how he managed to bend metal. It contains the answer to your question.
Never substitute a postflight for a preflight!