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ATC Capacity and Frequency Congestion

Another weekend has passed, another explosion of traffic, and ATC capacity and frequency congestion has become more real to me. A look at ATC capacity, frequency congestion and some solutions.

Another weekend has passed, another explosion of traffic, and ATC capacity and frequency congestion has become more real to me. With the weekend being the peak traffic days, I’ve had the fortune [or misfortune] of being called out or rostered for duty for at least the last six weekends in a row. On Saturday afternoon, I experienced the mother of all peak traffic levels. With aircraft stacked to what seems like infinity, aircraft were calling in reports and making requests faster than I can respond. I think any novice can conclude that ATC capacity was exceeded.
Working in a procedural control environment amplifies the effect of frequency congestion. Every request made by ATC for a position report or a passing level uses up valuable time that could otherwise be saved if some kind of surveillance system was employed. Ever so often, there will be requests to “say again” which further erodes valuable time. Murphy’s Law usually kicks in at that time and throws a monkey wrench into the whole operation. The ATIS broadcast can go down, an aircraft can develop an emergency or some vital communication link can go down. I experienced at least two of those simultaneously during the onslaught.
So what can air traffic controllers do to minimize the effect of this kind of overload? Here are a few suggestions:

  1. Bundling packets of information in a single transmission can be an option, but then there are limitations here. Too much information given in one transmission leads to “say again all before…….” or you may receive incorrect readback. This option is very tricky.
  2. Broadcast information that is general and that applies to multiple aircraft, like the aerodrome weather report.
  3. Issue conditional clearances like “after passing position ALPHA, descend to ….”, as opposed to “report ALPHA” followed by “descend to  ….” when the aircraft gets to ALPHA. At least one transmission can be eliminated here.
  4. Instruct pilots to report passing every thousand feet, or odd levels or even levels, if they have that opportunity at all.
  5. Suspend VFR operations.

The controller’s actions in these situations are however a mere drop in bucket to arrest the situation. The kind of actions necessary to combat ATC capacity problems must come from ATS authorities, and there are a myriad of things they can do. The Philippine authorities recently announced that they are looking at moving general aviation out of Manila International airport. The Philippine action I assume came after many other avenues were explored and exhausted.
Some of the tools available to authorities include scheduling or rescheduling of airline flights, splitting up ATC functions even further, employing the use of surveillance systems, employing the use of ATIS where none exists, and leaping into the future – the use of Controller Pilot Data Link Communication (CPDLC). Prior to employing any of these fixes, however, is the need to first determine what capacity exists, and document it.
According to ICAO Procedures for Air Navigation Service – Air Traffic Management (ANS ATM) document:

The number of aircraft provided with an ATC service shall not exceed that which can be safely handled by the ATC unit concerned under the prevailing circumstances. In order to define the maximum number of flights which can be safely accommodated, the appropriate ATS authority should assess and declare the ATC capacity for control areas, for control sectors within a control area and for aerodromes.
ATC capacity should be expressed as the maximum number of aircraft which can be accepted over a given period of time within the airspace or at the aerodrome concerned.

Capacity assessment

Here are some factors to consider when assessing ATC capacity:

  1. the level and type of ATS provided;
  2. the structural complexity of the control area, the control sector or the aerodrome concerned;
  3. controller workload, including control and coordination tasks to be performed;
  4. the types of communications, navigation and surveillance systems in use, their degree of technical reliability and availability as well as the availability of backup systems and/or procedures;
  5. availability of ATC systems providing controller support and alert functions; and
  6. any other factor or element deemed relevant to controller workload.

Having laid out my experience, I believe that positioning ATS systems to handle increased capacity seems like the plausible thing to do. It would ensure fairness for all parties involved. Controllers will be adequately equipped to handle peak traffic periods, aircraft operators can save fuel by adjusting their departure times accordingly, and safety can be assured for all. NEXTGEN, SESAR, BLUE MED, and all other such initiatives around the world aim at increasing ATC system capacity.
I know what the bean counters around the world are thinking, but ICAO in their wisdom has provided a means to pay for these developments. It’s called Air Navigation Facility (ANF) charges, and ICAO’s policies cater to every situation out there. We are not in unchartered waters.
It’s your turn: Tell me about your overload experience and how ANSPs can arrest the problem.

2 Responses


Wayne, as usual, you seem to have that particular knack for getting to the core of the matter with brevity. I think that every procedural ATS unit should plan for and identify its capacity and make every effort never to get there. I have forwarded to Ri, our project manager of the modernization project and ATS Manager.


CF, That brevity probably came from my many years in the profession. Too much rambling gets you nowhere. In the words from Max Ehrmann in his poem Desiderata, “speak your truth quietly and clearly”.

About Wayne Farley

I am Wayne, a career air traffic controller. Engage me while I share my thoughts, experience, and news from around the aviation world. A post titled “13 Characteristics of an Air Traffic Controller” written in 2010 went viral and established me as the unofficial ambassador of ATC.

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