by Pete Schoeninger
© 2021 October. All rights reserved!
Published in Midwest Flyer Magazine Online October/November 2021 Issue
Q: What is a thumb compression check? I note that it is mentioned frequently in accident reports.
A: After an airplane accident, if a pilot reports engine failure, an investigator may do two things initially to verify if the engine failed, or not. The first check that is completed will be to turn the engine and see if it turns freely. The second check is often a thumb compression check. That is done by removing a spark plug from a cylinder and putting your thumb over the spark plug hole. Then you turn the engine until the cylinder you have “thumbed” is coming up on compression. Your thumb will feel air trying to escape IF the cylinder is intact. But if there is internal damage, then probably there will not be any compression.
Q: Do you remember 80 Octane fuel, and can you tell me anything about it?
A: 80 Octane aviation gasoline, dyed red, was used by airplane engines with relatively low compression. Its demise was in the early 1980s for lack of demand. With the approval of non-leaded car gas as aviation fuel (available downtown for less $$ than aviation fuel), the demand for 80 Octane dropped. Another reason, beginning in about 1978 and from then on, both Piper and Cessna put engines requiring 100LL octane in their entry level airplanes, which further lessened the demand for 80 Octane.
Q: I heard about a guy in a remote area who does an annual inspection in one hour. Are there regulations that would prohibit a “quickie” annual inspection like this?
A: There is no minimum time specified in the Federal Aviation Regulations (FARs) to do an annual inspection, but find the required items (more than 50) at www.faa-aircraft-certification.com/43-appendix-d.html. In my opinion, no one can do all these items in one hour.
Q: I recently rode in a Cherokee Six which has four fuel tanks. About 10 minutes after takeoff, the pilot selected another tank for 5 minutes, then the third, then the fourth. I forgot to ask him why. Why run 5-10 minutes out of each tank shortly after takeoff?
A: If an airplane’s fuel tank(s) is filled full with cool fuel, and then that tank is exposed to heat like the sun shining on it, the fuel will expand, and vent overboard. If you take just a bit off the top of each tank, you may prevent this loss of fuel. Fans of Charles Lindbergh (like me) will remember that on his non-stop flight from New York to Paris, he burned about 15 minutes out of each tank before settling into his routine of an hour or two out of each tank as his flight progressed.
Q: A heard an old-timer tell a young pilot, if you have an emergency requiring an off-airport landing, do NOT land in a field with tall corn. Is this true, and if so, why?
A: Yes. From the air, a field of lush green tall corn looks like a perfect place for a gentle landing. But you may flip nose down violently on contact with the corn and smack the ground nose-first at a high rate of speed, which has seriously injured and killed people. If possible, try and touch down somewhere which will allow reasonable, instead of instant, deceleration.
EDITOR’S NOTE: Pete Schoeninger is a 40-year general aviation veteran, starting out as a line technician as a teenager, advancing through the ranks to become the co-owner and manager of a fixed base operation, and manager of an airport in a major metropolitan community. He welcomes questions and comments via email at PeterSchoeningerLLC@gmail.com.
DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of others, and refer to aircraft owner manuals, manufacturer recommendations, the Federal Aviation Regulations, FAA Aeronautical Information Manual and instructional materials for guidance on aeronautical matters.
