Avionics: Glass Cockpit, Transponder and GPS

A glass cockpit trades individual mechanical instruments for electronic displays. The primary flight display gathers attitude, airspeed, altitude, heading, and vertical speed onto one screen, while a multifunction display shows moving maps and engine information. Behind the screens, solid-state sensors such as an attitude and heading reference system and an air data computer replace the mechanical gyros and pitot-static instruments, but they need electrical power to work. The transponder answers ATC radar: Mode A sends only the assigned code, Mode C adds altitude reporting, and Mode S adds a data link. Pilots must know the standard VFR code of 1200 and the emergency codes — 7500 for hijack, 7600 for lost communications, and 7700 for a general emergency — and many operations require ADS-B Out to broadcast position. Finally, GPS uses satellite signals to fix position, and area navigation (RNAV) lets the airplane fly directly between points rather than following ground navaids. Approved GPS/WAAS equipment may support IFR RNAV (GPS) approaches — including approaches with vertical guidance such as LPV — when the equipment is approved, the navigation database is current, RAIM/WAAS availability is confirmed, and the published procedure is authorized. Together these avionics boost situational awareness while still demanding a pilot who understands their limits. Between steam gauges and full glass, many airplanes carry a horizontal situation indicator (HSI), which merges the heading indicator and the VOR/ILS course deviation indicator into one instrument: a rotating compass card shows heading under a fixed aircraft symbol while a course pointer and deviation bar show the selected course and left/right displacement. Combining heading and course on one face reduces workload and the chance of reverse-sensing errors.