POWERED flight in heavier-than-air machines has been with us for more than a century now - but that still doesn't mean we trust them, regardless of our regular corporate travel trips overseas.
It's estimated that at least one-in-five airline passengers are really nervous flyers, scared enough to fall into the category that we label the "white knuckle brigade".
And a whole lot more have smaller, niggling concerns that things might go wrong.
For these people, every little change in noise means that some sort of mechanical failure has occurred.
As the plane speeds along the runway for take-off, those bumps from below and the "ke-plunk, ke-plunk, ke-plunk" convince nervous flyers a wheel is about to fall off, causing the plane crash.
Just as they've got over that and they're safely airborne, there's a sort of whine and a thud. What's gone wrong now?
Nothing. Both noises are perfectly normal, and that's why, as part of fear-of-flying courses, a fair bit of time is spent on explaining to nervous passengers what these noises are.
That bumping on take-off, for example, is most likely the wheels of the plane passing over the centre lights of runways and taxi-ways - exactly the same effect you get when your car strikes cats' eyes on the road. The second noise is the wheels being retracted and locked in place.
So, what about some of the other sounds people worry about while most of their fellow passengers simply relax?
Although there can be variations between makes and models of aircraft - one set of overhead lockers might shudder and vibrate more than another, or an engine whine might be more penetrating and higher pitched - here's an explanation of the most common causes of concern.
All that banging and clattering while the plane is still at the boarding gate is the loading of luggage, cargo and food containers, much of it stored in a compartment beneath the floor of the passenger cabins, running on conveyors belts and hitting against stops.
Then doors are closed electronically. That's another whine, maybe a thump or vibration if you are sitting above them.
For a moment everything becomes still and lights flicker, as if power has been cut. It has.
Until this point, an auxiliary power unit has been providing electricity and running the air-conditioning.
It's also used to start the engines so, momentarily, air might stop flowing while all available power is used for this operation. Lights might flicker and cabin bells jingle.
The high-pitched screaming that follows means hydraulic pumps are building up pressure, with whirring sounds and whines as pilots check the operation of various parts of the plane.
The look of the wings can be scary. First, they seem to bounce a little. That's OK - they have to be flexible, with a little give so that they don't snap off.But they come apart as well. "Slats" at the front come out and down; "flaps" at the back hang down. This is to permit the shape of the wing to be changed, increasing its curve to provide more lift for take off. You'll hear a long hum as this happens.
Once at cruising altitude, slats and flaps are retracted, but ailerons at the end of the wings can be moved up or down to help the plane turn.
Spoilers, towards the back edge of the wing, also go up and down, to help provide lift, or act as air brakes.
Roaring and shuddering on take-off is normal because of the sheer power needed, and exhaust from the engines whirls and strikes the fuselage and tail causing vibration.
Chimes are not just used to alert passengers about seatbelts, but also to send signals to the crew: to be seated for take-off or landing, or to perform certain duties prior to landing. The crew may also be using their internal telephone system.Even during flight, the pilot is making constant adjustments: to maintain course and altitude, changing for weather conditions or the aircraft becoming lighter as it consumes fuel, to fine-tune cabin pressure or temperature. Meanwhile, the cabin crew is rattling around in the galley and passengers are flushing toilets.
Where air traffic is congested, as it is as you come in to land, pilots must manoeuvre more, hence more noises, power being increased or reduced, banking to turn on to another course.
Why bank? It's the same as a motorcyclist leaning over to go round a corner.
Landing involves doing all these things all over again, with flaps and slats and spoilers and elevators and engine power, with a great thump as the landing gear locks in place.
Tyres squeal on tarmac, followed by a great roar from the engines, as "thrust reversers" deflect the jet engine exhaust forward to create another form of braking.
All that remains now is for the chime that says you can undo your seatbelt. Now you know this you can calm down, corporate travel doesn't have to be so edgy!
The Fearless Flier's Handbook, by Debbie Seaman, published by Ten Speed Press - article presented by
corporate travel company BCD Express
