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When it's too hot to fly – and more weather that makes air travel dangerous

Planes need longer to take off in extreme heat
Planes need longer to take off in extreme heat

As if we needed any more evidence that it is simply too hot, dozens of flights have been cancelled because the aircraft are unable to work in such high temperatures.

Not in the UK, no, but in Phoenix, Arizona, where the mercury tickled 49C on Tuesday and threatens to do so again (London is comparatively chilly, with a forecast of 33C today).

Unfortunately for airlines, that is above the preferred operating temperatures of some planes, which means scheduled services must be rearranged. For what it’s worth, my preferred operating temperature is about 19C.

What flights were affected?

Predominantly regional flights leaving Phoenix Sky Harbour International were affected, using small Bombardier CRJ airliners, which have a maximum operating temperature of about 118F (48C). Some 40 flights were cancelled at the airport.

Bigger airliners, such as Boeing 747s or Airbus A320s, can cope in hotter conditions, 126F and 127F respectively, or just over 52C.

15 surprising things you didn't know about long-haul flights
15 surprising things you didn't know about long-haul flights

Why can't planes fly in the heat?

Hot air is less dense than cold air, meaning aircraft require more engine power to generate the same thrust and lift as they would in cooler climes. The conclusions are in part logistical and in part safety, as author and pilot Patrick Smith explains in his book, Cockpit Confidential.

“Hot air is less dense than cold, negatively affecting both lift and engine performance,” he writes. “The take-off roll will be longer and the climb shallower, and in very hot temperatures, a plane may no longer meet the safety margins for a particular runway - climb gradient parameters and the weight is determined for every take-off based on weather and runway length.

“Going a short distance with limited fuel is unlikely to be a problem, but full tanks or a heavy payload can put you up against the limits, and cargo or people will sometimes need to be bumped.”

Climate change could have 'have severe consequences for aircraft take-off performance, where high altitudes or short runways limit the payload or even the fuel-carrying capacity'

International Civil Aviation Organisation report

Smith also explains that aircraft components might begin to overheat and become damaged in extreme temperatures, with seals softening or melting.

Phoenix is not the only airport in the world to suffer from high temperatures. In August 2013 a British heatwave caused problems at London City Airport because its shorter runways did not provide enough room for aircraft to operate in the hot, thin air. The issue saw some passengers bumped from flights to lighten the planes.  

“Due to weather conditions, the take-off weight of the aircraft had to be reduced due to safety reasons,” a spokesman for airline Swiss told the Telegraph at the time.

“In very high temperatures it usually takes longer until the aircraft can actually take-off, and since London City Airport has a short airstrip the take-off weight needed to be reduced.”

Heat can cause issues at London City Airport
Heat can cause issues at London City Airport

Last year, a report from the International Civil Aviation Organisation warned that higher temperatures caused by climate change could “have severe consequences for aircraft take-off performance, where high altitudes or short runways limit the payload or even the fuel-carrying capacity”. 

The issue is why many airlines in the Middle East tend to schedule longer flights for the evening when it is cooler. 

Is it ever too cold?

In terms of flight, extreme cold does not present the same difficulties as heat does. Indeed, aircraft are designed to fly at 35,000 feet, where air temperatures fall to -51C.

But on the ground, falling mercury can spoil flight preparation: runways need to be gritted, windscreens de-iced and, in severe cold, the equipment required for refuelling can freeze.

Yakutsk in Russia has one of the coldest airports in the world - Credit: Copyright Amos Chapple/Amos Chapple
Yakutsk in Russia has one of the coldest airports in the world Credit: Copyright Amos Chapple/Amos Chapple

Is there such a thing as too windy to fly?

Gales are perhaps the most common weather element to affect flights – but not usually to the point of delay or cancellation.

Landings and take-offs are most critical times for dealing with high winds. To curtail the dangers posed by strong winds, manufacturers issue limits for maximum ground speeds, air speeds and cross speeds in which a plane can operate, based on “analytical computations and simulations”. For example, the Airbus A380 was designed to cope with crosswinds of 35 knots at take-off and 40 knots when landing.

According to the Civil Aviation Authority (CAA), however, the pilot decides whether a landing is safe – based on experience, not algorithms.

The CAA does enforce detailed weather reporting regulations for UK airports, however – set out in a 119-page document that makes for gripping reading – and airports must also provide half-hourly reports describing conditions along the runway.

secrets of air travel
secrets of air travel

Some airports are more susceptible to strong winds. Those flying into Leeds Bradford, the highest airport in Britain at 681 feet (208m), have seen their fair share of wobbly approaches.

In the windiest conditions “wingstrike” may occur – when, you’ve guessed it, a wing hits the runway. It doesn’t happen often, although one notable incident took place in 2008, when a Lufthansa A320 tried to land at Hamburg Airport amid gusts of up to 47 knots (54mph). The footage on YouTube is excruciating, but no one was hurt and the plane eventually touched down on another runway.

The phenomenon known as “wind shear” also poses a risk. This is a sudden change in wind speed and/or direction, causing turbulence or a rapid increase or decrease in velocity. A tricky scenario might see a pilot attempting to land into a headwind that suddenly turns into a tailwind. The result? Landing late and fast, and potentially overshooting the runway.

Can it be too wet to fly?

Similarly to windy weather, heavy rain has more of an impact on landing and runways, especially the former, when pilots need to adjust their anticipated landing distance according to how much water is on the runway.

However, most runways are constructed in such a way that though they might get wet, the chance of standing water is very slim.

Hydroplaning - where aircraft, or indeed any vehicle, essentially skids on the surface of a pool of water, rendering braking and steering redundant - is the most dangerous outcome of a wet runway. Pilots are sometimes advised to ensure a firm touchdown to prevent early skids.

Best of | Travel Truths
Best of | Travel Truths