Introduction

Of paramount importance in any aircraft is the

system (or systems) used for sensing and

indicating the aircraft’s attitude, heading, altitude

and speed. In early aircraft, these instruments

were simple electro-mechanical devices. Indeed,

when flying under Visual Flight Rules (VFR)

rather than Instrument Flight Rules (IFR) the

pilot’s most important source of information

about what the aircraft was doing would have

been the view out of the cockpit window!