Here is an alternate air door that was found to be loose and hanging in the open position. These doors, if installed and actuated by cable (as opposed to being held closed by magnets), should be regularly checked, and in fact can be checked on the preflight by using a flashlight and peering into the cowling near the exhaust stack exits. Being open like this causes dirty, unfiltered air to be constantly entering the engine. By the way, this will usually show up on an oil analysis as high silica. Also, it is allowing hot air to enter the intake system, thereby depriving the engine of the ability to make full rated power. It is like flying with the carburetor heat constantly on.
In Case You Missed it
When is an airplane in trim? At least to the pilot, the airplane is trimmed when no stick force is required to maintain equilibrium. So how do we achieve this? Barnaby Wainfan explains any number of ways to go about it, including the use of trimtabs, spring systems, sparrow strainers and variable incidence tails.