Communication, Surveillance and ATC Equipment
R/T discipline
Standard ICAO phraseology exists to remove ambiguity. A full readback is required for clearances and instructions relating to holding short, crossing, take-off, landing, altitude or flight level, heading, speed, SSR code and frequency. Readback errors must be corrected immediately. 'Say again' and 'confirm' are professional tools, not weaknesses.
Surveillance
Primary radar gives position only. Secondary radar (SSR) gives identity and, with Mode C, pressure altitude; Mode S adds a unique 24-bit aircraft address and downlinked selected altitude. ADS-B (1090 ES), ADS-C, multilateration and CPDLC extend coverage and support reduced separation. Standard identification methods include a position report over a known fix, a turn onto a specified heading, 'squawk ident' and PSR position correlation.
Emergency codes
7500 unlawful interference, 7600 radio failure, 7700 general emergency. On radio failure the pilot squawks 7600, follows the last acknowledged clearance and the published lost-communication procedure, and lands as soon as practicable.
Traps
Swapping 7500 and 7600; forgetting 8.33 kHz channel spacing; believing 'ident' is a clearance rather than an instruction to transmit the identification pulse; confusing Mode C (altitude) with Mode S (address and datalink).
Rule of thumb
If an instruction could put an aircraft on a runway, at an altitude, or on a heading, insist on a complete readback. Silence is not compliance.
Worked example
An aircraft reads back 'cleared to land runway 30' when the clearance was 'line up and wait runway 30'. Correct it immediately, in the same transmission, before any other traffic is affected.