Thunderstorms

Thunderstorms for fearful flyers because there is a belief that we just fly through them and accept whatever turbulence we get. The rules and regulation…and common sense …means that we don’t get any closer than 20 nautical miles to the centre of a storm.

You may feel that you’ve been closer but you haven’t. You may have been struck by lightning when you ‘ve been flying but that still doesn’t mean you’ve been in a storm. The reason a plane isn’t troubled by a lightning strike is that the plane is ‘insulated’ from the electricity because the fuselage acts as a Faraday’s Cage. Onboard weather radar shows the location and extent of any storm cells.

Thunderstorms have a limited life cycle, in terms of developing and decaying. Very occasionally storms will be self-perpetuating because as the storm develops it can begin to suck in air or on occasions the rising air becomes relatively warmer to the surrounding air rather than cooler. Under these circumstances, the storm will grow for longer than usual. One of the things pilots look out for when flying around a thunderstorm is the direction of the upper winds. We can tell by the shape of the cloud at its top which way the wind is blowing and we then steer around the storm from the windward side. In other words, if as we look at the storm we work out that the wind is blowing from our right to the left we’d steer to the right of the storm.
The rules say that we mustn’t fly closer than 20 nautical miles to the centre of a storm. Our weather radar shows the position of storms in relation to our route so it’s very easy to steer around them and still know where we are exactly in relation to our route (unlike the old days when we’d have to work it out all the time). In case you’re worrying Air Traffic Control allows aircraft to deviate to avoid ‘weather’ so there’s no problem in that respect. And aircraft flying the route earlier will have notified ATC so it doesn’t come as a surprise to them which means they can co-ordinate aircraft movements.

Facts about storms

Number of thunderstorms occurring at any given moment: 2,000

Number of lightning strikes every second: 100

Number of lightning strikes a day: 8 million

The average flash would light a 100 Watt light bulb for three months

The average lightning stroke is six miles long

A typical flash of folk lightning lasts for about 0.2 seconds

The temperature of lightning’s return stroke can reach 28,000 °C.

The temperature on the surface of the sun is around 6,000 °C

The Empire State Building in New York has been struck by lightning as much as 48 times in one day!

Lightning starts at the ground and goes up to the cloud.

More about thunderstorms

Many fearful flyers believe that they have flown through a thunderstorm and the reason for that they believe this is that they have flown when there are thunderstorms in the area, seen lightning, and have experienced turbulence at the same time.

International law says that aircraft may not fly through thunderstorms. Every commercial passenger carrying aircraft is fitted with airborne radar to detect thunderstorms and because this radar can locate thunderstorms as far away as 120 miles this gives a pilot plenty of time to take avoiding action.

In the cockpit of modern passenger carrying aircraft, this information is displayed geographically that is to say in relation to the aircraft’s position. Wherever a thunderstorm is located it is displayed to the pilot as an area of either green amber or red colouring on his compass system so that the pilot can see how far away it is in miles and where it is positioned in relation to his route.

Avoiding thunderstorms, therefore, is very simple because it requires only a small change of direction to avoid them. Air-traffic control receives reports from pilot’s when they deviate from the standard routings. And because all aircraft will be taking the same route to avoid the storms there is no conflict.

From a passenger’s point of view, the situation looks very different. At night lightning can be seen 100 of miles away but because of its intensity it can look very close. When flying past a thunderstorm the lightning is even more dramatic and because it will illuminate the insides of clouds and with irregular flashing it presents a ghostly picture, especially at night. However, there is no possibility that an aircraft will fly closer than 20 miles to the centre of the storm.

The area surrounding a thunderstorm will naturally be turbulent because of the vast amounts of air being drawn into a thunderstorm and being replenished by the surrounding air so there is always a constant exchange and movement of thousands of tons air in the vicinity of a storm. This movement of air will cause turbulence.

Aircraft struck by lightning are not in danger in any way. The dramatic nonsense that can be seen in the press has nothing to do with reality. I have been in aircraft that have been struck and I can promise you that there was no damage to the plane.

Pictures that you may have seen of nose cones being damaged are the result of hail not lightning and the nose cones are made of thin metal because that’s where the weather radar antenna is located … and it’s not pressurised.

Thunderstorms are a cause of concern to many passengers, especially someone with a fear of flying. A thundercloud is similar to the small fluffy clouds that appear on a bright sunny day. The difference is that the small continue to grow when the atmospheric conditions are right. Instead of the moisture within the cloud just condensing out and cooling, the air inside continues to go up. The air within stays warmer than the surrounding air and so it continues to grow and get higher.

When the air rises it draws in even more air … there’s a suction effect at the base and more and more air goes into the cloud, making it bigger and bigger. Eventually, the cloud stops growing, but this will be at 30-40 thousand feet compared with 6000 to 8000 for the small clouds.

The constant air movement causes the air molecules to rub against each other and make static electricity … and when the ‘charges‘ are right it makes a spark down to the ground or across to other clouds. This, of course, is lightning. At any one time, there are approximately 8000 active thunderstorms around the planet. Most of the lightning activity takes place within the cloud itself while the remaining 20% are ‘discharges’ that hit the ground.

Because the speed of light is so much greater than the speed of sound the flash that you see from lightning will be heard a long time before you hear the rumble of the thunder. The storm will be a mile away for every 5 seconds between seeing the flash and hearing the sound. The sound is caused by the electricity causing the molecules of air to vibrate. Around the bolt of lightning, the air is heated to about 30,000 degrees centigrade! You will not hear the thunder inside the plane, so if you see a Hollywood movie where the passengers can hear it … you know it’s rubbish.

The effect of lightning on an aircraft

I’m pretty certain that you will know that you’re in no danger if your plane is hit by lightning. Back in the 1700’s scientist Michael Faraday discovered that anything inside a metal cage (something that was continuous around the surface) would be safe from any electricity that touches the outside. This is why the lightning can’t get inside the plane.

At the extremities of the plane, there are things called static wicks, which look like artists paintbrushes, which discharge the electricity back into the air. However, you won’t see this happening!

The aircraft is very unlikely to be damaged physically by this although there may be scorching of the metal or paintwork… But you are NOT in any kind of danger. The electrical equipment on board, domestic and navigational will not be affected by lightning either. The engines will run normally and not be affected either. The only evidence of damage in the vicinity of a thunderstorm will be hail damage to the unpressurised nose cone which houses the weather radar.

Best wishes,

Captain Keith

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