Insider Series: Why Planes Sometimes Circle Before Landing
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TPG Contributor “Vic Vector” is an air traffic controller at a major ATC facility in the United States. In this installment of our “Insider Series,” he explains how holding patterns work and why your flight sometimes experiences airborne delays.
You anxiously look at your watch. Your flight was scheduled to land 10 minutes ago, the flight attendants have wrapped up service and are already strapped in their jumpseats, yet here you’re still aloft with no ground in sight. Then a chime rings overhead and you hear the PA crackle, followed by the dreaded words:
“Folks, from the flight deck, this is your captain speaking. Air traffic control has placed us in a holding pattern …”
So, what are holding patterns and why are they a necessary part of the national airspace system?
First, the basics. Per the FAA’s Instrument Flying Handbook, holding is “a predetermined maneuver that keeps aircraft within a specified airspace while awaiting further clearance from ATC.” Contrary to the title of this article, they aren’t actually circular, but rather are ovular — much like a NASCAR track. Holding patterns consist of two legs — inbound and outbound — which can be measured using either time or distance, though distance is most common in the world of commercial airliners.
Some commonly used holding patterns are published on maps and charts, while others are created by ATC on the fly, so to speak. There are many technical details regarding the ins and outs of holding patterns that pilots and controllers must be familiar with, but as a passenger you needn’t worry about any of them. You can simply think of a holding pattern as the aircraft equivalent of a traffic jam. However, unlike a highway, when traffic can’t proceed on an airway, planes can’t just pull over onto the shoulder.
The most basic cause of holding is volume — that is, too many planes trying to go to the same airport at the same time. Like multiple lanes merging together, aircraft approach major airports from several different directions, and while there are large-scale traffic initiatives designed to space out arrivals to busy airports during the most high-demand times, those don’t always work as intended. Controllers in the TRACON take these multiple feeds and blend them together, but sometimes the bottleneck becomes too great and they must shut off the sectors feeding them — who then have to hold the aircraft they have.
Weather is another common reason for holding aircraft. As I mentioned in my previous post, thunderstorms, snow and fog can all reduce visibility and even wreak havoc on the airspace system, potentially preventing aircraft from safely landing. Aircraft generally need at least a half-mile of visibility to land, though there are special approaches that some carriers can use to land at lower minima. If an aircraft’s visibility is reduced and it can’t see other traffic or the airport environment, this increases the separation standards TRACON controllers must employ. Putting more space between airplanes creates a logjam that will eventually ripple back until holding is required upstream to let the queue clear out.
Other factors that can reduce the arrival capacity of an airport are navigational aid outages, VIP movement or runway closures. For example, the current construction at New York-JFK has created large, daily miles-in-trail restrictions for aircraft headed that way — that is, controllers upstream are required to build in extra space between aircraft in order to make the arrival flow more manageable. Another looming concern for East Coast controllers has been Pope Francis’ visit to Philadelphia and Washington, DC, which officially kicks off this week, surely creating increased airspace demand and the potential for holding. And though it’s a far less predictable event, an aircraft emergency causing a runway closure will always trigger a holding pattern.
Holding-pattern delays could certainly inconvenience you, but fortunately, most are merely brief setbacks — and hopefully, short enough that aircraft won’t burn through their contingency fuel, an extra allotment that airline dispatchers and crews bring along when facing foreseeable airborne delays like weather and traveling pontiffs. In the event that pilots receive holding instructions from air traffic controllers, one of the most critical parts of that clearance is called an EFC (Expect Further Clearance) time, a controller’s best estimate of how long the aircraft can expect to hold before receiving clearance to proceed on course. Among other functions, the EFC allows aircraft to compare their expected holding time with how much spare gas they’ll have to hold.
When aircraft are running low on fuel during a holding pattern, controllers do their best to keep things moving, but sometimes a delay simply exceeds an airplane’s fuel. In these situations, aircraft are forced to divert to a different airport in order to refuel and wait out any additional delays on the ground before (hopefully) departing once again to the original destination. Thankfully, this worst case scenario isn’t particularly common.
I hope that your next flight isn’t forced to burn holes in the sky while waiting out some delay down the line, but if you do find yourself in a similar situation, now at least you’ll have a better idea of the fundamental causes behind it. And given the additional workload holding creates for us as controllers, rest assured that we also want to get your flight moving just as soon as we possibly can!