I was once on a flight over Africa where there was a lengthy delay before take-off owing to thunderstorms over the airport.  We encountered a further huge storm en route to our destination, and despite diverting around it, we experienced severe turbulence.

Boisterous drunks on board quietened up before becoming quite ill, and in addition to the seat-belt lights being kept on the whole way, the cabin crew were ordered to their seats by the captain.

Initially it was quite fun, but the fun stopped after a short while.  It was definitely a white-knuckle roller-coaster ride.

Turbulence gives one the impression that the aircraft is flying out of control, but it is not.  The aircraft may feel as if it is going to come apart.  Again, it will not do that.

Pilots try to avoid turbulence, largely for the sake of the passengers.  Cargo planes regularly fly through turbulence that passenger planes avoid, and they do not fall out of the air.

As uncomfortable as it was, the plane was never in any danger.  Not even if it had been struck by lightning, which commercial aircraft are designed to be able to cope with.  Your plane will almost always be under control of the autopilot when going through turbulence.  The autopilot has a special setting for turbulence in which it makes fewer, and more gentle corrections.  This relies on the tendency for aircraft to self-correct from most random flight changes resulting from air movements.

As with anything else, turbulence varies in extent and intensity.  There is a four-point scale for it:

• Light.  You can feel it, but you can walk around okay and the seatbelt lights remain off.

• Moderate.  It is still possible to walk and the cabin crew continue their duties but the seatbelt lights are put on.

• Severe.  What I experienced in my tropical flight above.  It is unusual.  Cabin crew are commanded to their seats.

• Extreme.  This is very rare because of all of the precautions taken to avoid it.

So, what are the real dangers associated with turbulence?

1. Loss of altitude when you are close to the ground.  If you are close to the ground and you get pushed down, the plane could hit the ground.  Thunderstorms can cause this and aircraft will not take off when a storm cloud is over the airport.  The pilot may divert the flight to a different airport to ensure safety, or the plane may be put into a holding pattern in a safe part of the sky until the weather in the region of the landing field has improved.

2. Gusts near the ground.  One pilot I spoke to told of a landing at Schipol when the plane was hit by a gust of wind just as he lined up the plane with the runway in a side-wind.  The jet’s wings rotated several degrees in a second and it was all he could do to level the wings and slam it on the ground.  Fortunately it was a cargo flight, so there were no complaints.  Passenger flights are typically diverted to another city if there are strong side-winds at the destination.

Aircraft and airports are both equipped to detect wind shear conditions that could otherwise be of danger to the plane.

3. Injury.  Passengers who are not belted in can be thrown against the roof of the cabin.  Persons have in fact died or have been seriously injured, particularly when flying in “clear air” with the seatbelt lights off when unexpected turbulence has been encountered.  Loose objects such as the drinks trolley can be flung against you, causing injury; and luggage can shift in the overhead lockers and spring the lock, dropping items on you.  The best you can do to protect yourself against this is to keep your seatbelt on for the whole flight.

4. Structural failure.  Over the years a disturbing number of light planes, not equipped with weather radar and with only basic instruments (flying according to Visual Flight Rules) have come to a bad end through falling apart in bad weather.  Commercial operators are better equipped and will reroute or reschedule if the weather outlook is poor.  The planes are also, as the cost would suggest, stronger and more reliable than private aircraft.  And the pilots are much less inclined to take unnecessary risks.

All things said, turbulence can be extremely uncomfortable but it is very rarely a source of real danger.

Photographed by Adrian Pingstone in August 2002 and released to the public domain

Before take-off

Once you’ve been welcomed aboard the flight by one of the cabin crew and located your seat, you can stow your luggage either in the overhead compartment or under the seat in front of you.  (The disadvantage of putting it under the seat is that it can reduce your available leg-room.)

Once all the passengers are boarded and seated, the cabin crew will start the safety briefing. They will show you how to do up and unbuckle your seatbelt, indicate where the exits are and show you how to inflate and deflate your lifejacket.  They will also show you how to operate the oxygen masks that will drop down from the ceiling if there is a sudden decompression.  (Decompression is very rare and few travellers have ever actually experienced it.)  They will do a final check down the aisles to make sure everyone has their safety belts on.  (The correct way is snug, and low down, across the hips.)

After being pushed back by a “tug” the aircraft will taxi to the runway under its own power.  It is customary for the captain to introduce himself and his team.  He will then make the announcement, “cabin crew, prepare cabin for departure”.  At this point you are just about set for take-off.

The cabin crew will “arm” the doors and check on each other to make sure that this has been done, before seating themselves.  The doors cannot be opened when the aeroplane is under way.  The “arming” is to ready the mechanisms that will operate the slides that will automatically deploy upon opening the doors when the airplane is on the surface.  (If the take-off is aborted, for instance, the doors will be opened, the slides will deploy, and everyone will be evacuated from the aircraft.)

Take-off

The pilot will line up the plane neatly on the runway.  The engines tone will rise as they push out maximum thrust.  The aircraft will leap forward eagerly and then gather speed quickly in order to get lift for take-off.  The acceleration will push you gently into your seat.  At a given speed (on a signal from the co-pilot) the pilot lifts the nose gently off the ground and the acceleration continues with the plane balanced on the main wheels, kept in place by the lift on the wings.  (You will usually not notice this).  For technically-minded readers, this phase of the takeoff is called “rotation”.)  Once the craft reaches take-off speed the pilot will pull back on the controls and lift the front of the plane into the air.  You may sometimes hear a faint thump as the wheels leave the ground.

From there the plane will climb sharply, gaining speed and altitude as it goes.  The rate of climb will gradually decrease and the plane will adjust to a move horizontal angle as it approaches cruising altitude.

Why the sharp angle after takeoff?  Once take-off has been achieved then the plane will fly an optimal route to get up to cruising altitude as soon as practically possible.  Quickly achieving altitude gives room for manoeuvre in case of any problems, and also gets the plane out of the immediate vicinity of the airport, reducing the crowding of the controlled airspace.  The aircraft becomes more efficient to run as it gets to the designed cruising speed and altitude.

Take-off noises

Shortly after takeoff the wheels and landing gear will be retracted into the aircraft fuselage, which can cause a slight thump, and the wheel-bay doors shut.  Once in the air, you will hear an assortment of sometimes quite loud noises.  These are normal.  The pilot’s actions are supported by hydraulic power, which ensures that he can control the rudder and other flight control surfaces, which would otherwise require inhuman strength.

Slats and flaps

It can be very disconcerting for first time flyers sitting at the window to see gaps appear in the wings before and during take-off, as shown in the picture accompanying this article.  The structures at the front of the wings are called slats.  The hinged ones at the back of the wing are called flaps.  A number of modern jets fly at a cruising speed of over 800 km/h (500 mph).  Without slats and flaps the takeoff speed would need to be a significant proportion of that speed!  By using slats and flaps the lift of the wing is significantly increased, essentially by increasing the curvature of the wing, which sharply reduces the speed necessary for flight.

After takeoff, once the speed has increased, sufficient lift is generated by the wings without the slats and flaps, due to the increased airspeed.  The devices are then progressively “packed away”.  This is also done using hydraulic power and the changing of the wing to its sleek cruising shape, without holes in it, will usually be accompanied by (sometimes loud) noises from the hydraulic system of the aircraft.

Now that you’re in the air, you should enjoy your flight.  This is one of the safest modes of public transport in the world today.