text: 1 Passing clouds 
  One of the pleasures of flying is seeing clouds close up. Even though they seem insubstantial they carry a considerable weight of water – around 500 tonnes in a small cumulus cloud. And water is denser than air. So why don’t clouds fall out of the sky like rain? They do. But the droplets take a long time to sink. An average cloud would take a year to fall one metre. 
  2 On cloud nine 
  Most of us are happy to label clouds “fluffy ones” or “nasty black ones ”, but meteorologists identify more than 50 cloud types based on shape and altitude. These fit into categories given numbers from one to nine. Cloud nine is the vast, towering cumulonimbus, so to be “on cloud nine” implies being on top of the world. 
  3 Around the rainbow 
  There’s no better place to see a rainbow than from a plane. Rainbows are produced when sunlight hits raindrops. We see a bow because the Earth gets in the way, but, from a plane, a rainbow is a complete circle. When passing over clouds, the plane’s shadow appears neatly in the centre of the effect. 
  4 Mr blue sky 
  Sunlight is white, containing all the colours of the spectrum but, as it passes through air, some of the light is scattered when it interacts with the gas molecules. Blue light scatters more than the lower-energy colours, so the blue appears to come from the sky. 
  5 There’s life out there 
  Apart from clouds and other planes, we don’t expect to see much directly outside a flying aircraft’s window, but the air is seething with bacterial life – as many as 1,800 different types of bacteria have been detected over cities and they can reach twice the cruising height of a plane. 
  6 Turbulence terror 
  Even the most experienced flyer can be turned green by turbulence. The outcome can be anything from repeated bumping to sudden, dramatic plunges. The good news for nervous flyers is that no modern airliner has ever been brought down by turbulence. People have been injured and occasionally killed when they are not strapped in, or get struck by poorly secured luggage – but the plane is not going to be knocked out of the sky. 
  7 In-flight radiation 
  When body scanners were introduced at airports there were radiation scares but the level produced is the same as passengers receive in one minute of flight. The Earth is constantly bombarded by cosmic rays, natural radiation from space that has more impact at altitude. 
  8 You can’t cure jet lag 
  The world is divided into time zones. The result is that long-haul travel results in a difference between local time and your body’s time, causing jet lag. However, its effects can be minimized by keeping food bland for 24 hours before travel, drinking plenty of fluids and living on your destination time from the moment you reach the aircraft. 
  9 Supersonic 747s 
  Many of us have travelled faster than sound. There are a number of jet streams in the upper atmosphere, notably on the journey from the US to Europe, where a temperature inversion causes a corridor of air to move as fast as 250mph. If an airliner with an airspeed of 550mph enters a jet stream, the result can be to fly at 800mph, above sound’s 740mph. 
  10 Flying through time 
  Time zones provide an artificial journey through time – but special relativity means that a flight involves actual time travel. It’s so minimal, though, that crossing the Atlantic weekly for 40 years would only move you 1/1,000th of a second into the future. 
  11 Terrible tea 
  Don’t blame the cabin attendant if your tea isn’t great. Water should be just under 100°C when it is poured on to tea leaves – but that isn’t possible on a plane. It’s impossible to get water beyond 90°C during flight – so choose coffee. 
  12 I can’t hear my food 
  Airline food has a reputation for being bland and tasteless. Some of the problem may not be poor catering, though. A plane is a noisy environment and there is evidence that food loses some of its savour when we are exposed to loud noises. 
  13 Needle in a haystack 
  With modern technology, it seems strange that Malaysian flight MH370 could disappear without a trace – yet, finding a missing aircraft is a needle- in-a-haystack problem. The plane knows its location, both from GPS and inertial tracking, but this information is not relayed elsewhere in real time. That would be perfectly possible. Ocean- going ships have had tracking since the 1980s – the limitation is not technology but a lack of legislation requiring it. 
  14 Volcanic fallout 
  Air travel can be cancelled by volcanic activity. Glass-like ash particles melt in the heat of the engine, then solidify on the rotors. A clear-skies policy in an ash cloud may be inconvenient – but the risks of ignoring the ash are clear. 
  15 The wing myth 
  For many years, we taught the wrong explanation for the way wings keep planes in the air. In fact, almost all a plane’s lift comes from Newton’s Third Law of Motion. The wing is shaped to push air downwards. As the air is pushed down, the wing gets an equal and opposite push upwards, lifting the plane. 
  16 Forget electric planes 
  When we see ultra-light, experimental, electric planes, it’s easy to assume there will soon be clean, green, electric airliners, but it won’t happen any time soon. Aircraft fuel packs in a remarkable amount of energy. Batteries are much less efficient. To provide the same energy as a tonne of fuel would take 100 tonnes of batteries – and a 747 uses 150 to 200 tonnes of fuel. Unless battery technology is made vastly more efficient, electric airliners won’t get off the ground. 
  17 Beware the vortex 
  Pilots often wait a long time to get clearance. This is to allow the air to settle after a previous take-off, as a plane’s wingtips generate vortices in the air, which can take two or three minutes to disperse. If the following aircraft set off immediately, the rapidly moving air would make the plane difficult to handle. The delay gives the air time to recover from the miniature whirlwinds caused by the preceding plane. 
  18 The doors aren’t locked 
  In practice, the doors on a plane don’t need to be locked. If you watch an aircraft door being opened, it swings in an unusual way. It first has to be opened inwards before manoeuvring it out of the way. Once the plane has taken off, a significant pressure difference soon builds up between the inside of the plane and the outside. This differential forces the door into place. To open it, you would have to pull against the air pressure, well beyond the capabilities of human muscles.