Instruments and Aircraft Systems
What the exam tests
You need a dispatcher-level understanding of aircraft instruments and systems so you can interpret crew reports, MEL effects, and abnormal situations. Expect pitot-static, gyroscopic, ADC/AHRS, FMS, autopilot, TCAS, EGPWS, weather radar, fuel, electrical, hydraulic, and pressurization questions.
Core systems
- Pitot pressure drives airspeed; static pressure drives altimeter and vertical speed. Blocked pitot or static ports cause misleading indications.
- ADC converts pneumatic inputs into digital air data; AHRS provides attitude and heading; FMS integrates navigation and performance.
- TCAS provides traffic alerts and resolution advisories; EGPWS provides terrain warnings.
- Weather radar detects precipitation and turbulence; it does not see clear-air turbulence or dry hail well.
- Fuel quantity, electrical, hydraulic, and pressurization status affect dispatch and diversion decisions.
Worked example
During climb, the captain reports the airspeed indicator behaving like an altimeter-increasing as the aircraft climbs-while the altimeter and vertical speed remain normal. This suggests a blocked pitot tube with the static system clear. The crew should cross-check standby instruments and use the approved unreliable-airspeed procedure. The dispatcher supports the diversion and avoids suggesting that the primary indicator is reliable.
Traps
Assuming one instrument is always correct; confusing pitot blockage with static blockage; treating TCAS as an avoidance command for the dispatcher; and ignoring MEL effects on autopilot, pressurization, or navigation. Use the aircraft-approved abnormal procedure.