March 08, 2019

Commercial Aviation Part 9

Neal Schier has returned with a sequel to his earlier post on why airline delays happen, looking at how delays get untangled.

Airline delays – how do they put it all back together?

Ah, airport delays — truly the Gordian Knot of the air transportation system. We all have experienced them and know how quickly they can grow into an unwieldy mess. What might start as a 30-minute departure delay for one flight, can sometimes end up in scores of cancellations—one of which, unfortunately, might be yours.

Now, if we were Alexander the Great, we could simply draw our sword and cut the knot in two. Instead, the airlines and the Air Traffic Control (ATC) authorities are left to unravel that knot thread by thread in order to “recover” scheduled air service.

Imagine you are at O’Hare airport and a winter storm starts to pound Chicago with heavy snow, ice, and strong winds. As you look out the terminal window it looks as if it is pouring snow it is coming down so fast. The giant snow plows are, of course, already at work and moving immense amounts of the snow, but there is a lot of ground to cover and progress is slow.

Pilots are reporting decreased braking effectiveness and have to slow their taxi speeds to a crawl. The wind direction has forced the tower controllers to use O’Hare’s least favorable “configuration” for takeoff and landings. Instead of the usual five active runways, only two are now usable and they will need to be plowed at some point.

Within the hour ATC is forced to put the departing flights on a ground stop—only arriving flights will be accepted. The “fortunate” ones are still at the gate and can deplane the passengers. Those “off gate” have to get back in line for an open gate as free space is at a premium. The departure screens are now a sea of red—with red signifying a cancelled or delayed flight.

The airlines, to their credit, have been proactive and had early on cancelled a number of flights in expectation of the bad weather. But the intensity of the storm is making a mockery of those good intentions—the conditions are far more severe than anticipated and are getting worse.

In the air, aircraft form up in holding patterns as far away from O’Hare as Kirksville, Missouri, Iowa City, Iowa, and Evansville, Indiana. Chicago bound flights getting ready to depart places like Los Angeles, Orlando, and New York are put on hold. What a bystander would think of as “just” a Midwest storm is now having a nationwide effect on air transportation.

Pilots in those holding patterns discuss their options and make a plan with their airline’s dispatchers back at HQ. They consider the fuel that they have on board and the both Chicago’s weather as well as that at the alternate airports. They know it is going to be tight and they are prepared to go somewhere else if need be.

On the ground at O’Hare, the airport manager has dedicated every resource to the snow clearing efforts. His goal is to keep at least two runways open for the arriving aircraft and he has been doing a valiant job until the unexpected happens—a landing 777 cannot stop in time and slides off the end of the runway.

Suddenly the airport is down to a single usable runway. The mechanics are quickly on the scene of the distressed 777, but it is going to be hours before they can move it. If you have seen the original Airport movie, with George Kennedy in the role of the cigar-chomping grizzled veteran mechanic Joe Patronne, you can imagine the work cut out for these dedicated souls.1

Now, what had been at least a somewhat manageable Chicago winter storm, has turned into a real problem. Who, after all, could have predicted that a wide-body 777 would end up in the mud? Result? The delays are now of an unknown duration—one cannot even guess.

A 777 after a very bad landing

Thirty minutes later however, it does get worse. There is a lot of ice mixed in with the snow and the last runway has to be closed for plowing and deicing. The mighty O’Hare airport has come to a complete stop.

Airlines cancel flights en masse. Long lines form at the service counters. Passengers work their phones to find out about possible hotel accommodations. In turn, the hotel managers are asking their drivers if it is even safe to try to reach the airport. Airport employees start to set up cots and break out pallets of water, infant formula, and Power Bars.

The pilots stuck in the holding patterns hear the bad news and start their diversions for new destinations like Denver, Pittsburg, and Cincinnati. The pilots in the cockpits of those Chicago bound planes in Los Angeles, New York, and Orlando are told to contact their company for “further guidance” — never a good sign when it comes to delays.

As you can see, the complexity is almost unimaginable. Like spectators flowing through an entry point at a sporting event, everything runs smoothly until there is a blockage at one of the turnstiles. Suddenly, the neat lines disappear and humans are bunched up in a jumble. The same is true for the air traffic industry—flow is good and blockage is bad—think of Lucy at the chocolate factory assembly line.

Fortunately, the air traffic system is designed to safely throttle down and ride out major schedule interruptions. True, it can be downright ugly at times and is certainly inconvenient, but there is a rhyme and reason underlying the recovery efforts and usually within 24 hours things are close to being back on track.

I made this set-up long on purpose to show you just how many gears are simultaneously spinning. “Great,” you say, “but how does everything get straightened out?” Well, although each airport differs, here is a generic outline of how it all happens.

The absolute prerequisite for unraveling the Gordian Knot is a well-defined line of communication. From the snow plow operators on O’Hare’s runways all the way to the command center of the Federal Aviation Administration’s (FAA) Air Traffic Control System Command Center (ATCSCC) located in Warrenton, Virginia.

First: The airport manager at O’Hare hears from his/her snowplow crew chiefs to find out what taxiways and runways are clear. He also has his finger on the pulse of the maintenance efforts to free the 777 that went off the runway. When he can, he passes update times to both the O’Hare ATC supervisors and the airlines. It all hinges on him and until he can get the “streets” cleared, everything is at a standstill.

Second: Once the airport taxiways, ramp, and at least one runway is open, the O’Hare ATC supervisor will communicate with the Chicago Terminal Radar Approach Control (TRACON). These are the controllers who are directly handling the lower altitude air traffic in and out of O’Hare, Midway, and other outlying airports. Working with the tower supervisor, the TRACON will hammer out an initial departure and arrival plan. Should this initial rate work out, they can ramp up the pace from there.

Third: Chicago TRACON advises Chicago Center of this proposed flow rate and they fold it into their traffic pattern. Chicago Center handles a much wider chunk of airspace—the altitudes above 18,000’ that overlay wide swaths of Illinois, Indiana, Iowa, etc.

Fourth: Overseeing all this is the ATC System Control Center back in Virginia. It has the final authority over air traffic within the National Airspace System (NAS) and its controllers and Traffic Management Specialists would have been directly involved with the knock-on effects of this storm. They were the ones, for example, who instituted the ground stops on all those Chicago-bound flights that getting ready to leave Los Angeles, Orlando, and New York. They are tasked to keep the broader picture in mind to minimize national disruptions. They have a lot of resources at hand and work hand-in-glove with the various enroute ATC Centers under their purview to keep things moving.

Fifth: The center of crisis management is at the airline’s headquarters. Here is where the aircraft routers sort through what planes they have on hand, which ones went to diversion airports, and tally the numbers of aircraft they expect to get in once the runways are open.

Their work is very much a “chicken or the egg” problem. How can you schedule an outbound flight if there is no airplane at the gate? Yes, software plays a leading role, but there is a surprising amount of human brainpower that goes into this. These routers pride themselves on being expert horse traders who can handle a lot of pressure. They shuffle, trade, and move assets around to get open airplanes to put passengers on.

The rule of thumb here is that they first try to get the aircraft they have on hand filled with passengers and “off the gate.” This starts to clear the passenger backlog and also makes room for inbound arrivals—including those aircraft that might have been stuck out on a taxiway during the shutdown. They constantly communicate with the airport and airline managers, ATC, and even with other airlines as they forge their plans.

Sixth: Once the routers figure out what airframes are where, the airline’s scheduling and reservations departments come into play. They are tasked with posting realistic schedules, gate assignments, and getting the passengers in the correct seats. There might have been a lot of aircraft substitutions and that means new seat assignments. International flights might take priority over domestic ones and a flight to LAX or JFK might bump out one to Albany or Harrisburg. Sadly, there might be even more cancellations until they get things sorted out but they are playing a game that spans their entire nationwide, and even international, system.

Seventh: Gate agents will draw upon the info that scheduling generates to try to get the passengers on and off the aircraft as needed.

Fortunately, technology continues to help with this. Little things like text messages have helped in keeping passengers better informed while software, linked with human ingenuity and experience, is getting better at cracking these shuffles of gates, airplanes, and departure times. I know these disruptions can be frustrating, and even anger inducing, but 24 hours is not too bad in the face of the worst that Mother Nature can conjure up.

The bottom line is that all the stakeholders, the ATC controllers, the airport managers, the airlines, and certainly the passengers, abhor even the slightest disruptions. They demand immediate attention and increased workloads and, as we discussed, pose a threat to the nationwide flow of planes and passengers. Cold comfort though it might be when you are stuck in a crowded terminal, the airlines and airport authorities really are working to minimize your inconveniences.

In the meantime, whenever you go to the airport, I suggest taking some extra food and a lot of reading material as you never know when a delay is at hand!

Neal Schier/March 2019

1 We still often respectfully refer to a mechanics as Joe Patronne in homage to this classic film figure.


  1. March 09, 2019Phil W. said...

    Neal hits the nail on the head with this subject. There are many "moving parts" to airport and airline operations. Neal provides an excellent insight into the decision making with irregular operations. After thirty years of flying for the airlines, I have to agree with Neal, always bring a snack I and have something to read. Phil W.

  2. March 10, 2019Bill Driver said...

    Well written sir! Like yourself, I have experienced similar scenarios as both a pilot and a passenger. It is almost impossible to convey the complexity of unraveling lengthy weather delays at a major airline.

  3. March 13, 2019Geezer said...

    Disclosure: I am a colleague of Neal’s so I am biased toward his writing, but I think this is a great overview of what happens in an irregular operations scenario. I like the thoroughness he brings to the task.

    Might I add though, that there have been those times when the system has failed in a big way. Just think of those times when the pax have been near hostages on aircraft stuck out on the taxiways.

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