Then we walk over to the trainer. We sit in it and I explain that nearly everything he sees in the panel is optional equipment. Even that radio we always talk on and the transponder we always turn to ALT are optional, along with most of the flight instruments.
We review the few required ones, and we look at the weight and balance and equipment list for the trainer to see if it was certified with any required equipment beyond that called out in FAR 91.205. Then I explain that whether or not we fly the plane with any of the optional equipment inoperative is up to the pilot-in-command. But if the PIC elects to fly the plane with an optional item not working it must first be placarded inoperative (INOP), before the flight not after. I tell my student that a piece of inoperative optional equipment can also be removed from the aircraft instead of placarded INOP, but that is done by a mechanic because it has to be recorded in the maintenance logs and the weight and balance must be changed. Removal is not a pilot activity. I end the lesson by emphasizing the distinct difference between required and optional equipment, and the different procedures to deal with each situation. When it comes time for the oral part of the checkride the student will make short work of the airworthiness questions.