Placards are prominently displayed on the panels of many general aviation aircraft, and for good reason—compliance with the message they relate is mandatory. FAR 91.9(a) says, in part, that no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards. In the Cub I fly, a placard on the center of the panel says, "REAR SEAT FOR SOLO FLYING." That means I must not solo from the front seat. It is an operating limitation. The limitations are generally set forth in the manufacturer’s flight manual or owner’s handbook for a particular aircraft. Some placards are directed by airworthiness directives.
Other types of placards that demand attention are the ones we use to identify inoperative instruments. FAR 91.213 addresses the conditions under which pilots may take off with inoperative instruments or equipment. In short, you may operate most light aircraft with inoperative instruments or equipment so long as they are not part of the VFR day type certification or otherwise required for a particular type of operation (day, night, IFR—see FAR 91.205) and they are deactivated and placarded “inoperative” or removed from the aircraft and the cockpit control placarded. Sometimes, this requires maintenance. And, in all cases, the pilot or the mechanic must make a determination that the inoperative instrument or equipment does not pose “a hazard to the aircraft.” There is more to 91.213 than can be summarized here, and I encourage you to read the regulation carefully if you plan to fly with something inoperative.
On the maintenance side of things, there is a bit of shared responsibility between pilots and mechanics. FAR 91.405 requires owners or operators to have inoperative instruments or equipment repaired, replaced, removed, or inspected at the next required inspection and ensure that placards are installed, as required. FAR 43.11 stipulates that the person performing required maintenance must placard items permitted to be inoperative under 91.213(d)(2) and shall add the items to the signed and dated list of discrepancies given to the owner or lessee.
Placards provide necessary information to aid in the safe operation of aircraft. The use of placards in accordance with the regulations also provides pilots an opportunity to go flying when certain instruments or equipment don’t work.
Learn more about AOPA Pilot Protection Services here.