From this answer, "A tennis ball stuffed in between two cylinders - a common flight instructor trick to see if students are doing a thorough preflight".

A place between the two cylinders is not the expected place for the tennis ball to be, but how does in general this "trick" work? I tried to Google but only pull out the mentioned answer.

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    $\begingroup$ If the student does a proper check, they will notice the tennis ball and remove it. If not, well, then the instructor has something to discuss with them. $\endgroup$ Nov 6, 2016 at 11:01
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    $\begingroup$ @J.Hougaard Please post answers as answers, rather than as comments. $\endgroup$ Nov 6, 2016 at 13:14

1 Answer 1


From aircraft flying handbook (page 2-9),

The pilot should also check for loose or foreign objects inside the cowling, such as bird nests, shop rags, and/or tools.

This tennis ball is a tool for instructor to see if a pilot does a proper walkaround of the airplane. A pilot should be able to detect this strange object inside the cowling easily if he/she does the walkaround properly.


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