Arrivals & ILS approaches ​

How arrival traffic, ILS approaches, and tower handoffs work in radarcontrol.io.

Overview ​

Arrivals enter at cruise altitude. You descend them (usually via a STAR), vector to the ILS, and hand off to tower. The full flow:

1. Entry - Aircraft enters sector at cruise altitude, assigned a STAR
2. STAR descent - Issue dv (descend via) to follow the published arrival procedure, or assign altitudes manually
3. Vectoring - Vector aircraft toward the ILS intercept zone
4. ILS Clearance - Clear aircraft for the ILS approach
5. Establish on Localizer - Aircraft captures and tracks the localizer
6. Glideslope Capture - Aircraft intercepts the glideslope and descends
7. Tower Contact - Hand off to tower before landing
8. Landing - Aircraft touches down and exits the simulation

Multiple arrivals at Denver: DAL814 established on the ILS 08 localizer (green), UAL291 turning base to final, SWA435 on downwind heading west, AAL102 descending to join the pattern.

ILS approach basics ​

What is an ILS? ​

The Instrument Landing System (ILS) provides precision lateral (localizer) and vertical (glideslope) guidance for landing. In radarcontrol.io:

• Localizer - Provides lateral guidance aligned with the runway centerline
• Glideslope - Provides a 3-degree descent path to the runway threshold
• Decision Height - Aircraft commits to landing at 200ft AGL

Learn more about ILS approaches

Approach states ​

Aircraft on approach progress through these states:

Interactive instructions ​

ILS clearance ​

Clear an aircraft for an ILS approach to a specific runway.

Syntax:

• i [RUNWAY] or ils [RUNWAY] - Clear ILS approach
• Runway format: 27L, 09R, 4R, 36, etc.

Examples:

DAL123 i 27L         # Clear ILS runway 27L
SWA456 ils 09        # Clear ILS runway 09
AAL789 i 4R          # Clear ILS runway 4 right

Tower contact ​

Hand off the aircraft to tower control. This is required for landing to complete.

Syntax:

• t or twr or tower - Contact tower

Examples:

DAL123 twr           # Contact tower
SWA456 t             # Contact tower (short form)

Go-around ​

Instruct an aircraft to abort the approach and climb.

Syntax:

• ga - Go around

Examples:

DAL123 ga            # Go around

After a go-around:

• Aircraft climbs to 3,000ft above airport elevation
• Aircraft regains controllability
• Runway protection is cleared
• You can re-vector for another approach

Combined instructions ​

Instructions can be chained together:

DAL123 c50 i 27L            # Descend to 5000ft, clear ILS 27L
SWA456 i 09R twr            # Clear ILS 09R and contact tower immediately
AAL789 c30 s200 i 4R        # Descend FL30, speed 200, clear ILS 4R

Vectoring to the ILS ​

Aircraft at various stages of the ILS approach: DAL814 established on the localizer (green), UAL291 turning base to intercept, SWA435 on downwind, AAL102 descending to join the sequence.

Intercept geometry ​

For a successful ILS intercept, aircraft must be:

• Heading: Within 30° of the runway heading
• Distance: 5-20nm from the threshold
• Altitude: At or below glideslope altitude (+500ft margin)
• Side: Approaching from in front of the threshold (not behind)

Vectoring procedure ​

1. Descend the aircraft to an appropriate altitude (typically 3,000-6,000ft depending on distance)
2. Turn the aircraft toward the localizer at an intercept angle of 20-30°
3. Clear ILS when within the intercept zone

Example Sequence:

DAL123 c60                   # Descend to FL60 (6,000ft)
DAL123 h270                  # Turn heading 270 (30° intercept to RWY 24)
DAL123 i 24L                 # Clear ILS runway 24L

Localizer extension ​

The radar display shows the localizer centerline extending from each runway. Use this visual aid to:

• Plan your intercept vectors
• Judge when to turn aircraft toward the localizer
• Verify aircraft are established on centerline

Scripting API ​

Arrival events ​

onApproachCleared(callback) ​

Called when an aircraft is cleared for an ILS approach.

onApproachCleared((event) => {
  log(`${event.cs} cleared ILS ${event.runway} at ${event.airport}`);
});

Event Object:

{
  cs: string,        // Aircraft callsign
  airport: string,   // Airport ICAO code
  runway: string     // Runway identifier
}

onILSEstablished(callback) ​

Called when an aircraft establishes on the localizer.

onILSEstablished((event) => {
  log(`${event.cs} established ILS ${event.runway}`);
});

onTowerContact(callback) ​

Called when an aircraft is handed off to tower.

onTowerContact((event) => {
  log(`${event.cs} contact tower for ${event.runway}`);
});

onLanding(callback) ​

Called when an aircraft touches down.

onLanding((event) => {
  log(`${event.cs} landed ${event.airport} runway ${event.runway}`);
});

onGoAround(callback) ​

Called when an aircraft executes a go-around.

onGoAround((event) => {
  log(`${event.cs} going around: ${event.reason}`);
});

onUnableILS(callback) ​

Called when an aircraft cannot accept an ILS approach (pilot reports "unable").

onUnableILS((event) => {
  log(`${event.cs} unable ILS ${event.runway}: ${event.reason}`);
});

Reason values:

• 'heading' - Aircraft heading too far from runway
• 'too_close' - Less than 5nm from threshold
• 'too_far' - More than 20nm from threshold
• 'too_high' - Above glideslope + 500ft
• 'wrong_side' - Behind the runway threshold
• 'no_ils' - Runway has no ILS equipment

Aircraft control methods ​

clearILS(runway) ​

Clear the aircraft for an ILS approach.

onSpawn((aircraft) => {
  // For arrivals, set up approach
  if (aircraft.destinationAirport) {
    aircraft.over("FINAL", (ac) => {
      ac.clearILS("27L");
    });
  }
});

Returns: boolean - true if clearance was successful

contactTower() ​

Hand off the aircraft to tower control.

onILSEstablished((event) => {
  const ac = traffic.byCallsign(event.cs);
  if (ac) {
    // Hand off to tower when established
    ac.contactTower();
  }
});

goAround() ​

Instruct the aircraft to go around.

// Go around if runway becomes occupied
onTick(({ traffic }) => {
  traffic.all().forEach(ac => {
    if (ac.approachState === 'final' && isRunwayBlocked(ac)) {
      ac.goAround();
    }
  });
});

Aircraft properties ​

Aircraft on approach have additional properties:

aircraft.approachState    // 'vectoring' | 'intercepting' | 'established' | 'final' | 'landing'
aircraft.clearedILS       // boolean - has been cleared for ILS
aircraft.contactedTower   // boolean - has been handed to tower
aircraft.destinationAirport // string - ICAO code of destination

CenterAPI methods ​

Low-level approach control methods:

center.clearILS(callsign, runway)      // Clear for ILS
center.contactTower(callsign)          // Contact tower
center.goAround(callsign)              // Go around
center.isOnApproach(callsign)          // Check if on approach
center.getApproachState(callsign)      // Get current state
center.isRunwayProtected(airport, rwy) // Check runway protection

Example: automated arrival handling ​

// Handle arrivals
onSpawn((aircraft) => {
  if (!aircraft.destinationAirport) return;

  log(`${aircraft.cs} arrival for ${aircraft.destinationAirport}`);

  // Descend toward approach altitude
  aircraft.descend(6000);
  aircraft.speed(250);

  // Direct to final approach fix
  aircraft.direct("FINAL");
});

// Clear ILS when in position
onTick(({ traffic }) => {
  traffic.all().forEach(ac => {
    if (ac.destinationAirport && !ac.clearedILS) {
      // Try to clear ILS
      const cleared = ac.clearILS("27L");
      if (cleared) {
        log(`${ac.cs} cleared ILS 27L`);
      }
    }
  });
});

// Hand off to tower when established
onILSEstablished((event) => {
  const ac = traffic.byCallsign(event.cs);
  if (ac) {
    ac.contactTower();
    log(`${event.cs} contact tower`);
  }
});

// Log landings
onLanding((event) => {
  log(`${event.cs} landed safely!`);
});

Holding patterns ​

When arrival demand exceeds runway capacity, use holding patterns to delay aircraft before sequencing them for approach.

JBU522 holding at GOROC at FL200 with standard right turns. The orange racetrack shows the hold pattern shape.

When to hold ​

• More arrivals than the runway can handle
• Runway temporarily closed (go-around, vehicle on runway)
• Weather requiring spacing adjustments
• Waiting for a gap in departure flow

Hold commands ​

AAL123 h MERIT             # Hold at MERIT (right turns, 4nm legs)
DAL456 h MERIT L           # Hold at MERIT, left turns
UAL789 h ROBUC R 10        # Hold at ROBUC, right turns, 10nm legs
SWA321 h MERIT L 10 e 3600 # Hold with EFC at time 3600
AAL123 xhld                # Exit hold, resume route

See the full hold command reference for all options.

Scripting holds ​

// Hold arrivals when runway is protected
onTick(({ traffic }) => {
  traffic.all().forEach(ac => {
    if (ac.destinationAirport && !ac.clearedILS) {
      if (center.isRunwayProtected(ac.destinationAirport, "27L")) {
        ac.hold("MERIT");
      }
    }
  });
});

Runway protection ​

The simulator enforces runway protection to prevent multiple aircraft from approaching the same runway simultaneously.

• Protection Zone: 5nm from threshold
• One aircraft at a time per runway
• Protection clears when aircraft lands or goes around

Check runway status:

const occupied = center.isRunwayProtected("KJFK", "27L");
if (occupied) {
  log("Runway 27L is protected - hold aircraft");
}

Approach speed reference ​

Default approach speeds by aircraft type:

Troubleshooting ​

"Unable ILS" messages ​

Aircraft not landing ​

If an aircraft reaches the runway but doesn't land:

• Check tower contact - Did you issue twr instruction?
• Aircraft will not complete landing without tower handoff

Go-around situations ​

Consider a go-around when:

• Runway becomes occupied
• Aircraft is too high on glideslope
• Spacing from preceding aircraft is too tight
• Weather conditions change

Quick reference ​

ILS INSTRUCTIONS
  i 27L, ils 27L     Clear ILS runway 27L
  t, twr, tower      Contact tower (required for landing)
  ga                 Go around

HOLDING
  h MERIT            Hold at MERIT (right turns, 4nm legs)
  h MERIT L 10       Hold left turns, 10nm legs
  xhld               Exit hold, resume route

COMBINED EXAMPLES
  DAL123 c50 i 27L           Descend 5000, clear ILS
  SWA456 i 09R twr           Clear ILS 09R, contact tower
  AAL789 ga                  Go around

INTERCEPT REQUIREMENTS
  Heading:  Within 30° of runway heading
  Distance: 5-20nm from threshold
  Altitude: Below glideslope + 500ft

APPROACH STATES
  vectoring     → intercepting → established → final → landing

SCRIPTING EVENTS
  onApproachCleared, onILSEstablished, onTowerContact
  onLanding, onGoAround, onUnableILS