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Clearly, it is necessary and possible for ATC to control air traffic without radar:

  • not every control tower has a radar feed from a TRACON or their own radar site
  • over the ocean, aircraft are beyond the range of radar for long periods of time
  • Going back several decades, large stretches of domestic airspace in the US didn't have radar coverage

What are the methods by which air traffic is controlled and managed without radar?

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2 Answers 2

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Without radar or other surveillance technology (such as Wide Area Multilateration, ADS-B), ATC uses procedural control.

In procedural control, air traffic controllers build up situational awareness by using pilot reports, estimates and visual observations, combined with knowledge of routes, navigation beacons, fixes and other reporting points, plus support tools such as flight strips.

ICAO Doc 4444 (PANS ATM), Chapter 5 contains the procedures and procedural separation minima to be applied by ATC.

The separation minima for procedural control are much larger than for radar control (typically 5 NM or 3 NM), and are often expressed in minutes (e.g. 15 minutes).

Example of procedural separation minima from Doc 4444, showing 15 minute or 10 minute separation, depending on the presence of navaids. Example of procedural separation minima from Doc 4444, showing 15 minutes or 10 minutes separation minima, depending on the presence of navaids. Source: ICAO Doc 4444

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Question: How does ATC control traffic without radar?

Answer: In the U.S., the Air Traffic Control system was designed to be operated without radar. Even with the wide availability of ATC radar the current underlying "non-radar" procedural rules and criteria are still an inherent and necessary component of how (primarily) IFR aircraft are routed and, to a lesser extent, separated.

With some noted exceptions (e.g., published "Radar Required" procedures, RNAV routing), Standard Instrument Departures (SIDs), VOR Airways, Standard Terminal Arrivals (STARs) and non-RNAV Instrument Approach Procedures (IAPs) (some exceptions apply) are all examples and part of the non-radar structural design underlying the ATC system.

Although the use of radar and ATC radar procedures are the predominant tools (being replaced by ADS-B), the existing non-radar procedures can be utilized for handling and separating IFR aircraft even if all of the radar systems/antennas were to cease operating. ATC system capacity and efficiency would suffer, but IFR aircraft could still be routed and separated (using non-radar procedures) the same as they were prior to radar becoming available for air traffic control purposes many years ago.

Lastly, normally in today's ATC environment a co-mingling of non-radar and radar procedures for routing and separation is used as necessary depending on the existing circumstances. These circumstances vary during an IFR flight from departure to destination and are usually functionally transparent to the pilot.

Most non-radar ATC procedures are typically more complex to explain and apply than radar procedures. As such, a deeper understanding can be gained by reviewing Chapter 6 of the FAA's JO 7110.65Z (Air Traffic Control Handbook).

Non-radar IFR separation procedures are (primarily) divided into 3 main categories - Longitudinal, Lateral, and Vertical: (Below are samples and do not explain the full use of each category.)

(Refer to the Chapter 6 link above for a full understanding and use of each category)

Longitudinal Separation:

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Lateral Separation:

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Vertical Separation:

enter image description here

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    $\begingroup$ The 44 KTS in "44 KTS or faster" seems very slow. Is that an anachronism or applies to helicopters & other slow moving traffic? $\endgroup$
    – copper.hat
    Commented Nov 21, 2022 at 0:36
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    $\begingroup$ @copper.hat As in the example in the upper right longitudinal separation diagram, the trailing aircraft starts out 5 miles behind the lead aircraft and the lead aircraft is 44 kts or more faster (then the 5 mile lead will be increasing). So, for example, the lead aircraft maintains 250 kts and the trailing aircraft maintains 200 kts (50 knots slower). $\endgroup$
    – user22445
    Commented Nov 21, 2022 at 0:52
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    $\begingroup$ Thanks @757toga, I see, so "..than the following aircraft" is implied. $\endgroup$
    – copper.hat
    Commented Nov 21, 2022 at 2:17
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    $\begingroup$ @copper.hat Paragraph 6-4-2 a. specifically mentions the "following aircraft." $\endgroup$
    – user22445
    Commented Nov 21, 2022 at 2:22

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