Now this stuff is important because of two reasons. If it's inop you can't fly, so to keep your birds in the air, you've got to troubleshoot at the least, and increasingly with spares and with ramp test equipment, you're able to test and recertify. Secondly, these are some of the few avionic systems that are on the clock. The Out of Phase Tasks require every 24 months, to test and recertify the ATC surveillance system of altitude, the transponder (in whatever modes are installed), and of the altimeter and pitot-static system.