# What is the optimal sequence of departures and arrivals on a single runway?

When in a peak load scenario with plenty of departing & arriving aircraft to keep the ATC pipeline full, are there considerations that make a certain sequence of Departures / Arrivals that optimizes throughput?

For specificity, let us assume a single runway in use and no general aviation aircraft with predominantly jet traffic and multiple runway entry & exit taxiways available. Including high speed exit turnoffs.

I typically see a sequence something like:

 Dep-Dep-Arr-Dep-Dep-Arr


But an alternative optimum might turn out to be:

Dep-Arr-Dep-Arr-Dep-Arr


etc.

I realize that the specifics will depend on the exact aircraft etc. but just to use an idealized model what would result from typical operating constraints. e.g. You need to allow a certain separation during approach but you can have multiple aircraft lined up for take off. So is the potential to squeeze departures into the "holes" higher? Also, you can clear a second departure after a first far more rapidly, than the landing-to-landing interval right?

Just wondering, if you had to set up a formal optimization model what sort of parameters & constraints should go into the model as inputs.

A follow up question: Say you had two runways available in parallel & widely spaced apart. Does it make sense (for throughput) to dedicate one to landings & another to takeoffs or is it more efficient to mix landings & takeoffs on both runways?

R18L: Dep-Dep-Dep-Dep-Dep-Dep-Dep-Dep-Dep
R18R: Arr-Arr-Arr-Arr-Arr-Arr-Arr-Arr-Arr


vs

R18L: Dep-Dep-Arr-Dep-Dep-Arr-Dep-Dep-Arr
R18R: Dep-Dep-Arr-Dep-Dep-Arr-Dep-Dep-Arr


PS. If further simplifying assumptions are necessary, let's imagine a hypothetical airport serving a single aircraft type, say A320 only. Or assume any type you will to be representative of a wide class of aircraft just to get the modelling started.

• Interesting question. Not answers, just elements of the problem: Airport Operations --- Airport Runway Optimization --- Models for Aircraft Landing Optimization – mins Apr 10 '16 at 9:07
• This is a pretty broad question that's going to be dependent on a lot of factors. Some airports will have more departures at one time of the day and more arrivals at another. In your first example there are twice as many departures as arrivals whereas in your second they are even. Most airports with multiple runways use separate arrival and departure runways – TomMcW Apr 10 '16 at 9:08
• @TomMcW Another way to ask is: If as an airport I have a certain number of arrivals & departures to handle, as an ATC is it easier if they came segregated or mixed? – curious_cat Apr 10 '16 at 11:51
• @mins Nice links. One of them talks about "optimal departure sequence". That's sort of close to that I am asking. My question is about an optimal departure+arrival sequence. – curious_cat Apr 10 '16 at 12:00
• Try looking at NATS Gatwick Arrivals Review for information about the 900 flights a day on a single runway. You should also look at time based separation currently trialling at Heathrow and expected to be deployed at Gatwick – user23614 Apr 12 '16 at 15:23