Aircraft General Knowledge - Instrumentation
Instrumentation covers the sensors, computers and displays that give the crew attitude, altitude, speed, heading, engine and navigation data. The exam favours failure modes: what the instrument shows when a source is blocked, frozen or lost.
Core instruments
- Pitot-static: pitot pressure feeds the airspeed indicator; static pressure feeds altimeter, VSI and airspeed. A blocked pitot leaves the ASI behaving like an altimeter; a blocked static source causes altitude, speed and VSI errors.
- Altimeter: set QNH for altitude above mean sea level, QFE for height above a datum, and standard 1013.25 hPa above transition altitude. Always cross-check against terrain and procedure minima.
- Gyroscopes: rigidity and precession underlie attitude and heading references; AHRS/IRS replace or supplement them.
- ADC and EFIS: air data computers combine pitot-static and temperature inputs; display failures can be partial.
- EICAS/ECAM: colour and attention-getting logic distinguish warnings, cautions and advisories.
- GPWS/EGPWS, TCAS, weather radar and radio altimeter each have specific limitations.
Worked example
On climb, the altimeter is set to 1013 hPa while the aircraft is still below transition altitude. The indicated altitude is not the aerodrome QNH altitude; it is a pressure altitude. Before descending, the crew must set the correct QNH and cross-check the altimeter against the procedure minimum.
Traps
Believing the VSI responds instantly; treating the turn coordinator as a bank-angle indicator; ignoring that TCAS resolution advisories must be followed unless safety requires otherwise; and assuming all EFIS screens fail together. Static blockage can make the ASI over-read in climb and under-read in descent.