CTR — Control Zone

What is a CTR

The CTR (Control Zone) is a controlled airspace extending from the surface up to a defined upper level, around one or more controlled aerodromes.

Its primary function is to protect arriving, departing, and pattern traffic from interference by unauthorized VFR. It's the control tower's "home yard".

Typical characteristics:

• Lower limit: SFC (surface)
• Upper limit: variable, usually 2000-4500 ft AGL — depends on the airport
• Plan view: irregular, follows geography (mountains, obstacles, standard routes)
• Airspace class: typically C, D, or E in Europe

Typical Swiss dimensions and classes

Swiss CTRs vary in size and class:

Almost all Swiss CTRs are class D, meaning: VFR admitted, clearance required, separation provided between IFR but not between VFR (traffic information service between VFR).

How to enter a CTR

To cross or land in a controlled CTR, VFR must:

1. Establish radio contact with competent TWR (or APPROACH if large airport, then handed to TWR)
2. Announce intentions (transit, landing, departure)
3. Wait for explicit clearance
4. Execute the assigned route or procedure

VFR reference points

Each CTR publishes in its AIP (AD 2 section + VAC charts) standard VFR reference points. These are easily recognizable geographic points (a castle, a bridge, a lake, a hill) used to:

• Report your position unambiguously
• Define standard entry and exit routes
• Provide "hold" points when ATC wants to keep VFR outside the CTR temporarily

Examples at Lugano: Mendrisio, Bironico, Lago di Lugano centro, Monte Bre. Should be studied before flying on the VFR Manual Switzerland chart.

Active and inactive CTRs

A CTR can be active or inactive. It's active when the tower is operating; inactive outside AIP hours. When inactive:

• The CTR transforms into class G (uncontrolled)
• Traffic is managed on the AERO frequency (self-information)
• VFR self-announce and visually separate

CTR and VFR weather minima

VFR in CTR (class D) has visibility and cloud distance minima:

• Visibility: 5 km at 3000 ft AMSL and above, 1500 m below 3000 ft
• Cloud distance: 1000 ft vertical, 1500 m horizontal (above 3000 ft)
• In marginal conditions: you can request Special VFR from TWR

See also APPROACH for the SVFR procedure.

Summary — to remember

1. CTR = controlled column of air from the surface, around a controlled airport.
2. Class D in Switzerland (clearance required for VFR, no VFR-VFR separation).
3. Entry requires explicit clearance — "cleared to enter".
4. VFR reference points are listed in the AIP/VFR Manual.
5. If the tower isn't operating, the CTR becomes class G (self-information).
6. Special VFR in marginal conditions, on request.

Sources

• ICAO Annex 11 — Air Traffic Services
• ICAO Doc 4444 — PANS-ATM
• AIP Switzerland — AD 2 (for each aerodrome) and ENR 6
• VFR Manual Switzerland — VAC charts and procedures
• Aero Locarno · Subject 090 — VFR Communications