Ground Delays - a hold by any other name...

"Goose Air Thirteen, I have a holding clearance when you're ready to copy..." Not the words a pilot loves to hear. A hold usually means late arrivals, wasted fuel and increased workload. Thankfully, holding times have been reduced at destinations using flow control programs.

It works something like this: busy ATC centers like Chicago O'Hare routinely use data such as staffing levels and weather forecasts along with runway configurations to calculate a maximum number of aircraft they can accept each hour. They then look at the inbound flight plans to see where this capacity might be exceeded. When over-flow is inevitable they start assigning slot times. Using each flight's estimated en route time they calculate a take-off window at our point of origin. This information is sent along to us as a wheels up time. I make it sound like there's a room full of controllers somewhere using Casio calculators and an old abacus to work all this out, but I'm assured they hardly ever use the abacus. In fact, the last time I visited a center and saw the flow control program in action, it was running on a PC desktop computer.

Once we have our wheels up assignment we begin figuring out how to deal with it. We may be able to delay our push-back, but if other flights need our gate we will taxi out to some holding point on the airport. Depending how much time we have to kill, we might choose to shutdown the engines while we wait. Tower controllers work with us to ensure we get airborne within the five-minute window allowed.

Once en route we may experience more minor delays. For example, at places where the airways converge we might be assigned a short hold or 'S' turns and speed restrictions as arrival controllers work us into their conga line.

Of course, throw a few surprise thunderstorms into the mix, and it's back to square one. As one old captain used to quip; "That's why we get paid the big bucks!" -- for those times when the best of plans go astray.

Flightaware graphs of ORD arrivals and departures;
http://flightaware.com/analysis/graphs/airport/KORD