Correct Answer : Altimeter, airspeed indicator, artificial horizon and heading indicator
Explanation : Avionics update is one of the effective ways to extend the life of an aircraft. The technology is undergoing an exponential growth and is hence viable to use multifunctional CRT displays in places of mechanical dials. However, the basic T instruments, the altimeter, airspeed indicator, artificial horizon and heading indicator are retained because of their importance in flight control. In modern cockpits, even these are being replaced by solid-state devices with LCD display.
