Why the second-busiest international airport is often so nightmarishly fragile

Airline passengers in London today are still feeling the effects of a brief computer glitch at an air-traffic control center yesterday. The system was out of action for less than an hour, but the knock-on effects—delays, cancellations, and re-routed flights—still linger.

This is inevitable after any sort of unexpected disruption at a major travel hub, but the effect is amplified at Heathrow, which—despite carrying the second-most international passengers, after Dubai—is by some measures the world’s most fragile major airport. This is not because the systems at London’s largest airport are particularly prone to meltdown or its workers are substandard, but because it routinely runs at full capacity, which makes clearing any backlog of cancelled or delayed flights a nightmare.


The Institute of Air Transport and Airport Research has created a measure of airport capacity utilization, which compares the average traffic volume during operating hours to the volume during an airport’s 5% peak-hour volume in a year. By this measure, Heathrow is by far the most capacity-constrained in the world, with traffic running at around 85% of its peak volume at any hour of the day.

(Institute of Air Transport and Airport Research)

Bigger airports with more runways, like Chicago O’Hare and Atlanta Hartsfield-Jackson, can handle almost twice as many flights as Heathrow (which has only two runways) without putting nearly as big a strain on their operations.

Expanding London’s airport capacity has been a controversial political issue for years, thanks to the capital’s strict planning permission and resistance from local residents along flight paths. Mayor Boris Johnson’s plan for a four-runway airport to be built on reclaimed land in the Thames was nixed last year by a government-backed commission. The commission is instead considering competing proposals to expand Heathrow or Gatwick, although it won’t make a final recommendation until after the general election in May next year, with approval subject to the whims of whatever government is in charge at the time.

Arrivals in red, departures in green. (Heathrow)

Across Europe, aviation experts warn that airport capacity won’t keep up with projected passenger demand. An EU-funded group recently warned that there could be more than 20 “Heathrow-like airports” in Europe by 2035.

This was not a compliment for the London airport, but a byword for a dangerously stretched facility that leads to avoidable delays and forgone economic opportunities. The travellers who are delayed by the annoyingly common holding patterns imposed on Heathrow-bound flights, as well as the passengers still languishing in London today thanks to a software hiccup yesterday, will recognize the gravity of this warning.

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