CNS Systems and Surveillance
Communications, navigation, surveillance
Know the CNS systems: VHF and HF communications, VOR, DME, NDB, ILS, GNSS, primary and secondary radar, and ADS-B. Understand the difference between primary radar, which uses skin returns, and secondary radar, which uses transponder replies. Know the meaning of Mode A, C and S, and the role of ADS-B and multilateration.
Surveillance use
Know how radar identification is established, the meaning of a radar contact, and the conditions for terminating radar service. Understand the effect of radar coverage gaps, especially in mountainous terrain, and the need for alternative separation when coverage is lost. Know the phraseology for radar vectoring and the meaning of "radar contact lost".
Traps in questions
A common trap is assuming ADS-B provides the same separation as radar without the required conditions. Another is confusing a transponder code with a callsign. Questions also test the meaning of a squawk and the emergency codes.
Rule of thumb
Identify the sensor, then the service, then the separation. Worked example: an aircraft reports "radar contact lost". The controller must apply non-radar separation or re-establish identification before continuing to provide radar separation; the loss does not automatically terminate control, but it changes the separation method.
Aircraft Performance
Performance fundamentals
Know the factors affecting aircraft performance: weight, altitude, temperature, wind, runway condition and configuration. Understand the meaning of V speeds, take-off and landing distances, climb gradients, and the effect of density altitude. In Bolivia, high-elevation aerodromes make density altitude a critical factor.
Operational relevance for ATC
Controllers must understand why an aircraft requests a longer runway, a lower level or a delayed climb. Know the meaning of a performance-limited climb and the effect of a heavy aircraft on departure routing. Understand the relationship between weight and wake turbulence category, and the effect of temperature on engine performance.
Traps in questions
Questions often test the effect of increasing altitude or temperature on take-off distance, or the meaning of a V speed. Another trap is assuming all aircraft of the same type have identical performance. Watch for questions on the effect of wind on the take-off roll.
Rule of thumb
Higher, hotter, heavier and wetter all mean longer distances and lower climb performance. Worked example: at a high-elevation aerodrome on a hot afternoon, an aircraft may be unable to comply with a standard SID climb gradient. The controller should expect a request for a lower initial level or a different departure procedure, and must coordinate before issuing the clearance.
Wake Turbulence and Types
Categories and causes
Wake turbulence comes from wingtip vortices, which are strongest when the generating aircraft is heavy, clean and slow. ICAO wake categories are based on maximum certificated take-off mass: Light, Medium, Heavy and Super. Know the category boundaries and the effect of aircraft configuration on vortex strength.
Separation application
Know the wake turbulence separation minima for departures and arrivals behind heavier aircraft, including time-based and distance-based minima. Understand the effect of intersection departures, parallel runways and crossing runways. Know the phraseology for a wake turbulence caution and the pilot's responsibility to accept or refuse.
Traps in questions
Questions often test the category of a specific aircraft or the time interval behind a Heavy. Another trap is assuming wake turbulence separation applies only to IFR flights; it applies to VFR as well. Watch for questions on the effect of wind on vortex movement.
Rule of thumb
Light behind Heavy needs the largest interval; Heavy behind Heavy needs less. Worked example: a Light aircraft departs behind a Heavy. The controller applies the prescribed time interval and issues a wake turbulence caution; the pilot may request a delay, and the controller must not reduce the interval below the minimum even if the pilot accepts.
Communications, Phraseology and Coordination
Standard phraseology
Use ICAO standard phraseology, with Spanish as the normal language in Bolivia and English available on request. Know the structure of a clearance, the readback requirement, and the meaning of "roger", "wilco", "affirm", "negative" and "standby". Know the phonetic alphabet and the pronunciation of numbers, including the use of "decimal" and "thousand".
Coordination
Coordination between ATS units uses prescribed formats and must be complete before responsibility is transferred. Know the meaning of an estimate, a boundary estimate and a handoff. Understand the need to read back clearances and to correct errors immediately. Emergency communications use the distress and urgency signals.
Traps in questions
Questions often test the correct readback items, or the difference between "roger" and "wilco". Another trap is assuming a clearance is valid without readback, or misusing "standby" as an approval. Watch for questions on the use of the phrase "cleared" versus "expect".
Rule of thumb
If it changes the flight path, it must be read back. Worked example: the controller issues "ABC123, descend to flight level 200". The pilot must read back the level; "roger" alone is insufficient because the instruction changes the flight path. If the pilot reads back a wrong level, the controller corrects immediately.