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In the US, airlines or airports report two figures regarding canceled flights:

the total time away from the gate and the single longest time away from the gate.

and regarding diverted flights:

the total time on the tarmac at the diversion airport and the longest single time on the tarmac.

I don't understand this distinction, nor the individuall phrases.

  • What is a "single time"? A single time period out of multiple ones?
  • Why would a plane be away from the gate multiple times? i.e. leave the gate, return to the/a gate, leave again and return again?
  • Why would a diverted plane be on the tarmac multiple times at the same airport?
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Planes can be stuck on the tarmac for long enough periods that they no longer have enough fuel to make it to their destination safely, so they have to return to a gate to get more--and as soon as they're done, they typically get kicked off that gate because other planes have the same problem, so they go back out to sit on the tarmac. Of course, while they're at the gate they usually load more food and drinks as well, which are also often running low if you've been sitting that long.

The reason this is tracked specially is that when the plane returns to the gate, passengers are allowed to deplane. So, a single time away from the gate is how long passengers are "trapped" on the plane, which is psychologically and politically different from how late the flight leaves.

If a plane is diverted to an alternate airport, the same scenarios play out as above at the origin airport with the same reasons.

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  • $\begingroup$ Huh. I didn't realize the fuel consumption at rest really that significant. Also, are you sure this is the single and only reason for returning to the gate? $\endgroup$ – einpoklum Nov 3 '18 at 19:13
  • $\begingroup$ The ground burn rate isn't significant, but it's not zero either. IFR flights must have enough fuel at takeoff to fly to their destination and then their alternate plus 45 minutes for variations in routing/winds. Airlines may load some extra for expected ground delays, but too much means burning more fuel to carry extra weight around, which adds up fast for thousands of flights per day. They'd rather occasionally return to the gate for a top-up--and to give angry passengers a chance to deplane. $\endgroup$ – StephenS Nov 3 '18 at 20:19
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The US regulations have the tarmac delay rules, which apply to extended delays where passengers are left sitting on the tarmac. This followed a variety of incidents where passengers were kept on board non-moving aircraft for long periods of time, sometimes without access to food and water. The rules are a bit complicated with various exceptions, but broadly:

How long can an airline keep me on a DEPARTING flight before the airline is required to start moving the airplane to a location where passengers can safely get off?

For flights departing from a U.S. airport, airlines are required to begin to move the airplane to a location where passengers can safely get off before 3 hours for domestic flights and 4 hours for international flights.

So yes, a flight can potentially have multiple tarmac delays. For example, a flight could potentially leave the gate on time, sit on the tarmac for 2.5 hours, return to the gate (to allow passengers a chance to get off, as is required), leave the gate, wait another hour, be cancelled, and return to the gate. The airline would report both all the time the plane was away from the gate (2.5 + 1 = 3.5 hours) and the longest period the plane was away from the gate (2.5 hours).

What is a "single time"? A single time period out of multiple ones?

Yes. If the flight sits waiting on the tarmac for more than one period, the "single time" is whichever period was the longest.

Why would a plane be away from the gate multiple times? i.e. leave the gate, return to the/a gate, leave again and return again?

It could happen for a number of reasons. One would be that the plane returned to the gate to comply with the rule and allow passengers an opportunity to get off after 3-4 hours delay. The plane might return to the gate for a maintenance issue. They could be waiting out bad weather or a situation where an airport is not accepting flights. Most airlines seek to avoid this, but it can happen, and the reporting requirement is intended to capture data about how long it takes when it does.

Why would a diverted plane be on the tarmac multiple times at the same airport?

The same reasons. I had this happen once due to a tornado. The flight diverted, we went to a gate, we went back to the tarmac to wait for better weather, the flight was cancelled, so we went back to a gate again. It's an unusual situation, but it can happen.

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