The World From Your Airplane Window

Airport gates are traditionally numbered, with one exception: You'll usually find that gate 13 is missing. Although few people truly suffer from triskaidekaphobia, the number 13 is still often regarded as unlucky, something airlines and airports are enthusiastic to avoid.

Of course, in airports with no Gate 13, some passengers still consider gate 14 unlucky because ‘it’s really gate 13’. To prevent this from happening, Gate 12 in London Heathrow’s Terminal Four is at one end of the building, and Gate 14 is at the other end. As you never see the two gates side by side, it’s not obvious that Gate 13 is missing.

After what can seem like a long wait, it’s time for pushback. The aircraft reverses away from the stand and taxies off to the end of the runway. Unlike a car, there’s no power to the wheels in a plane; most of the maneuvering on the ground is driven by the aircraft engines. This is not a very efficient way to travel when the plane isn’t in the air, particularly in reverse, so to get away from the terminal an aircraft tug (sometimes called a pushback tractor) is usually brought in.

The tugs used on 747s are typically 200-300 horsepower—less than a high-performance car. In principle, an airliner can back away from the terminal using reverse thrust. This involves the crude technique of placing a deflector behind the jet engines, so the blast of air is pushed towards the front of the plane. Reverse thrust is usually deployed on landing to slow the aircraft down—this is what is being engaged when you hear the engines suddenly surge as you touch the ground. But it isn’t practical to use reverse thrust when close to a terminal (‘on stand’ in airline parlance). The blast from the engines is liable to send any debris on the ground hurtling towards the glass of the building, which is why tugs are used instead.

You may wonder, given the inefficiency of taxiing on jet engines, why the tug doesn’t take the plane all the way to the runway. Virgin Atlantic did come up with the idea of doing just this in 2006. The idea was to pull the plane to a ‘starting grid’ at the end of the runway. This would have produced significant fuel savings—Virgin reckoned that they could save two tonnes of CO2 per flight, as well as reducing noise and cleaning up the air near the terminal.

Unfortunately, despite its green credentials, the technique soon had to be shelved. This was partly because airports were not willing to provide the starting grid locations, which would have produced delays while tugs were decoupled and moved clear of the jet blast. But more significantly, the aircraft manufacturers warned that increasing the amount of towing would put too much strain on the undercarriage, meaning the struts that hold the wheels would have to be replaced more frequently.

One drink you might be served on board your flight could be a little disappointing—and not just because you might have to drink it out of a plastic cup. That’s a nice cup of tea. Tea enthusiasts like their tea made with boiling water—which means getting the water up to 100˚C [212˚F]. That’s never going to happen on a plane. Not because the cabin crew can’t be bothered to do it properly, but because it’s impossible to get water up to 100˚C on board the aircraft.

At the pressure of an aircraft cabin—the equivalent of being up to 8,000 feet above sea level—water boils at around 90˚C [194˚F], and that’s as hot as your tea is going to get.

Imagine if you had one of the water boilers from the galley on the wing of the aircraft. A cup of tea made with this water would produce a very unappetizing drink. With the reduced air pressure at around 40,000 feet, water boils at just 53˚C [127˚F].

If the tea disappoints, the chances are that the food will as well. This probably isn’t too much of a surprise. Unless you’re travelling in Business or First Class, airline food doesn’t have a good reputation. Yet this isn’t necessarily the fault of the airline. There are physical effects that can reduce the tastiness of the food. There could be some impact from low cabin pressure, the very dry air on board and the way meals are reheated, but one surprising cause is the level of background noise.

There’s a constant noise in flight, both from the engines and the air systems (not to mention fellow passengers). Research published in 2010 looked at the way noise influences our experience of food. Test subjects were blindfolded and asked to rate various foods as they were exposed to differing levels of background noise. When the noise was louder they tended to rate food as less sweet or salty, but more crunchy.

So far the view has been superb. But at some point on the journey you're likely to pass into cloud. Clouds are divided by type [here stratocumulus mix with cumulus in the foreground, with cumulus beyond]. These correspond both to the height at which the cloud is located and the shape and density of the cloud. There are technically a great number of cloud types—around 52.

The original classification identified three families of clouds. These were cirrus (from the Latin of 'hair'—hence wispy, thin clouds), cumulus (meaning a 'heap' or 'pile' for obvious reasons), and stratus (meaning a 'layer' or 'sheet').

This early structuring was done in 1802 by a pharmacist and amateur meteorologist from London, Luke Howard, and picked up by the likes of landscape painter John Constable, who produced reams of cloud studies. Later, in 1896, the clouds were grouped into nine basic forms, each given a number from 1 to 9. This was later revised to include ten cloud forms—1 to 10. But the World Meteorological Organization (WMO), the body responsible for the numbering, later changed the range again to be 0 to 9.

This final change of numbering was for a surprisingly romantic reason. The cloud type with the number 9 (which later briefly became 10) was the cumulonimbus. Although this is classified as a low cloud because its base starts well down, the peaks of a giant cumulonimbus climb higher than any other cloud. If you were perched on top of a cumulonimbus you could consider yourself on top of the world—and this is where the expression 'on cloud 9' comes from. The WMO realized they were being spoilsports turning a cloud 9 into a cloud 10, so they reversed their decision.