Let Simon Calder be your guide through the turbulent skies of the travel world with his very own alphabet of aviation.

AIRPASS

America's ‘Inter- Rail of the Skies’ is back, at least for a few thousand lucky travellers. Until the mid-90s, Delta and Northwest airlines offered foreign visitors the chance to travel anywhere they wanted in the continental US for a flat fare of around $299 (¤208) a month. You simply turned up at the airport, asked for a seat for your chosen destination and joined the standby queue. After a bit of nailbiting, you usually found you were on the plane — and on the rare occasion it was full, you just flew somewhere else on the network.

First Northwest, then Delta, abandoned the offer: selling a month's worth of air travel for less than the price of a one-way ticket from Chicago to Los Angeles made no economic sense, especially when passengers such as me were repeatedly opting for overnight transcontinental flights to save on hotel accommodation.

This month, though, the airpass makes a comeback on an airline that is not even a decade old — JetBlue ( jetblue.com), the stylish, low-cost start-up that has become one of America's major carriers and is in partnership with Aer Lingus. With bookings hit by the recession, the airline decided to fill seats by launching a limited-edition $599 (€418) pass for travel from now to early October. The security issues raised by the terrorist attacks of September 11 have put paid to the carefree, “Well, if I can't go to Miami, I'll head for Minneapolis” spirit. Instead, passengers have to book a seat at least three days in advance.

The airline says it's delighted by the response. Other carriers will be watching closely, and, in the most dismal autumn for years, may well decide to follow suit.

BANKRUPTCY

Zoom went bust a year ago. The transatlantic low-cost carrier was the latest in a very long line of airlines where accountancy had prevailed over optimism. Within a fortnight, it was followed by XL Airways.

A calamity? Well, not for many of the hundreds of thousands of travellers affected. Whenever an airline goes bust — and expect a few to fall over the edge this autumn — anyone who has booked a flight as part of a package holiday is well protected (though the XL collapse has put a strain on the Atol refund system).

Passengers who have booked direct and paid using a credit card are covered by the bank; you can also claim for contingent liabilities, such as paying much more than the original fare to get home. In practice, though, other airlines step in to help rescue stranded passengers on a standby basis at low fares. So even the final category — people who have paid in cash or by debit card, and become unsecured creditors of a very bankrupt airline — do not usually fare too badly.

CHECK-IN

Like cheques, pagers and George Michael, check-in seems an anachronism in the 21st century. These days, most of us travel on tickets that are either impossible or very expensive to change. So it's odd that we are obliged to line up at a desk in an airport in order to announce our intention to board the aircraft.

With airlines desperate to cut costs, many are keen to persuade us to check in online and print our own boarding passes. Luggage is taken to a ‘bag drop’, sometimes optimistically prefixed ‘fast’.

The days of a smiling young man or woman waiting to register your attendance at the airport in readiness for your flight look numbered. Ryanair plans to abolish the check checkin concept altogether from October this year.

But while it prevails, these strategies could help to smooth your path when travelling with one of the more traditional airlines:

Arrive very early. Most check-in desks open two hours ahead of the departure time (though this can be up to three hours for long-haul flights). Line up very early if, for example, you want to bag seats together or secure an emergencyexit seat.

Arrive very late (but a few minutes before the deadline). If you don't mind where you sit, survey the queue when you arrive at the airport. If it is dauntingly long, go and have a coffee and return 10 minutes before check-in closes. You are likely to find the line has vanished. You may occasionally also get lucky: if you are flying on a multi-class aircraft and all the economy seats have gone, you could be upgraded to business class.

If the check-in desk handles multiple flights (increasingly the case), scrutinise the label that is attached to your luggage to make sure it shows your destination. At least the luggage then has a sporting chance of joining you on the flight if it is tagged to the right destination.

DREAMLINER

Although the Airbus A380 did not start flying until well into the first decade of the 21st century, it is effectively a 20th-century airliner in terms of technology and passenger comfort—albeit bigger than anything that has gone before.

For a dramatically different experience, improving everything from cabin pressure (comfortably closer to sea level) to bigger windows, you need the Boeing 787 Dreamliner.

So, too, do dozens of airlines that have ordered the revolutionary new twin-engined jet. But the Seattle-based manufacturer has had huge problems getting the plane in the air. When it takes off, British Airways, Monarch, Thomson and Virgin Atlantic are in the order book.

ENVIRONMENT

Air travel has many adverse effects on the environment. The damage starts on the ground, from the noise and air pollution caused by both aircraft and the extra traffic generated by the passengers and staff.In the air, the world's airlines pump out a vast amount of carbon dioxide at high altitude. To limit the ill-effects of your travel, choose an airline that operates modern aircraft and packs in the passengers.

FREQUENT-FLYER POINTS

In 1980, the industry- standard ‘load factor’ was just 70pc — in other words, three out of 10 seats were empty. Then someone at American Airlines hit on a wizard wheeze. To build customer loyalty, why not offer some of those empty seats to the passengers who flew most often on AA? The frequent-flyer scheme was born, and has been much emulated since.

But as life has got trickier for airlines, ‘earning and burning’ (accruing and redeeming) frequentflyer points has become more difficult. Planes are flying fuller, meaning fewer seats are open for reward passengers — especially at busy times. In addition, ‘free’ flights can be far from free: on a trip I booked from London to Boston and back, the ever-increasing taxes, fees and charges amounted to ¤264, which meant I was paying more than half the cash fare for the privilege of spending my frequent-flyer points.

To make the most of your entitlement on the traditional airlines' schemes:

Stay with the programme: to maximise your earnings, choose a single airline alliance and its associated rental car and hotel partner. Look for special promotions that can rapidly earn you extra miles, or tier points that give you senior status and lounge access. For example, American Airlines had a cut-price first-class promotion, selling seats for not a lot more than the flexible economy fare, which allowed canny travellers to amass points several times faster than in the cheap seats. You can find out about the deals on websites such as the frequent travellers' online forum flyertalk.com.

As with any flight these days, the earlier you book, the better the deal you're likely to get. Book reward travel many weeks or, ideally, months in advance to get the widest choice of dates.

To maximise the cash value of your miles, ‘spend’ them on uncompetitive, niche routes where fares are disproportionately high. For example, British Airways between London and Bermuda.

If there are no free seats for when you want to travel, pay for the cheapest ticket then use your points to upgrade to business class.

Check when your miles expire. These days, airlines are exercising their rights to rewrite the rules and reduce your entitlement to zero, with minimal warning.

GIBRALTAR

The corner of the Iberian peninsula that is forever British has an airport that is, in many respects, unique. The runway, mainly on reclaimed land, runs east-west to bisect the narrow northsouth isthmus linking the 30,000 inhabitants with the Spanish border. As with the Swiss/French airports of Geneva and Basel, you can choose which country you enter after exiting the aircraft. But unlike in those cities' airports, the main road between Gibraltar and the rest of the world crosses the runway, and is closed during the takeoff and landing of flights.

HANDLING COMPANIES

The sign may say Ryanair, British Airways or easyJet, but in practice the staff you meet at airports are likely to be employed by an independent ground-handling company. Indeed, relatively few airline/ airport combos, such as BA at Heathrow and New York JFK, or easyJet at key Spanish airports, employ their own ground staff. It's more common for airlines to contract ground handlers to look after everything from check-in to the ‘ramp’ (organising boarding, baggage, refuelling and departure) — especially at airports where a particular airline might have only one or two departures a day.

At Dublin Airport, Aer Lingus and Ryanair both provide passenger and baggage-handling services for their clients, while at larger European airports, airlines play off one ground-handler against the other, with Servisair, Swissport, Aviance and Menzies Aviation.

Airlines can also ask other airlines to work for them, and this is particularly the case within the big alliances. So at Heathrow, for example, members of the Star Alliance work together.

INDIA

The world's secondmost populous country is now the bargain-basement destination in terms of air fares, as well as living and travelling costs when you get there.

Five years ago, the minimum fare from London to the commercial capital, Mumbai, was more than €570.

Today, you still can’t fly direct from Ireland, but you can get there for half as much, for example on Qatar Airways from Gatwick via Doha.

Also in India, low-cost airlines are rapidly enticing travellers away from the world's greatest transport undertaking, Indian Railways. Kingfisher, GoAir and Spice- Jet are among the options — for example, GoAir has nine flights a day between Delhi and Mumbai, with plenty of seats available at less than ¤34 each way.

JET A-1:

Standard aviation fuel is remarkably similar to domestic paraffin. Airlines are currently paying 60p a litre or less for the stuff — plus VAT, which they can reclaim. A standard, narrowbodied Boeing 737-800 or Airbus A320, with a full load of passengers and crew, will burn around three tonnes an hour in the cruise, costing the airline around ¤1,373 (roughly ¤7.44 per passenger).

Spikes in the price of oil in recent years have led many airlines to impose fuel surcharges. On Valentine's Day last year, British Airways and Virgin Atlantic issued a joint statement confessing to pricefixing on these surcharges, and have started paying out refunds to anyone who flew long-haul with either airline between August 11, 2004, and March 23, 2006.

See airpassengerrefund.co.uk.

KILOGRAM

This is the standard unit of measurement for baggage. The cost of carrying more than your entitlement used to be calculated at 1pc of the firstclass fare for the journey you are making — which, these days, is an archaic concept. Many carriers have a fixed charge for each extra bag, or excess kilograms. Most have a limit of 15kg; if you turn up at the airport with more, Ryanair charges ¤15 per kg for excess.

LOST LUGGAGE

Most ‘lost’ luggage isn't lost at all; it is left behind at your departure airport, erroneously sent to a different destination or — and this is the main problem —mis-sorted at a connecting hub. You should soon get it delivered to your home or hotel, and, meanwhile, are entitled to claim a reasonable and modest amount on essentials.

If your bags are permanently lost, the Montreal Convention specifies the maximum entitlement for lost baggage as 1,000SDR (Special Drawing Rights, a virtual currency calculated from weighted values of the US dollar, euro, yen and pound), which is now worth close to ¤1,114.

Much better, of course, is to stop your bags from going astray in the first place. The best ways to do that are as follows:

Don't check anything in unless you absolutely have to.

If you must check in luggage, try to book a non-stop flight — bags are much more likely to go missing when being transferred at airports such as Amsterdam, Paris Charles de Gaulle and Heathrow.

Make sure that you have labelled the inside of your luggage with your name and address, in case the external labels are torn off while in the tender care of airport baggage systems.

MAASTRICHT

The small airport in the far south of Holland where Europe's first short-haul, low-cost air service began in 1984: Virgin Atlantic flew a small Vickers Viscount to Gatwick as a ‘feeder’ link for its New York flight. The airline later abandoned it, leaving the field clear for easyJet.

Maastricht is also the venue for Eurocontrol's Upper Airspace Control Centre. While you're at 37,000 feet, people in an undistinguished building on the edge of this Dutch city are looking after you. Progressively, nations are ceding control of their skies to the pan-European body, which makes for smoother and more efficient use of airspace; the ultimate aim is a ‘single European sky’.

On June 27 last year, Maastricht handled an all-time record of 34,476 flights in a single day — equivalent to a take-off every two-and-a-half seconds, if they were evenly spread.

The controllers do not do this out of the goodness of their hearts; the charge for controlling a two-hour flight of a standard narrow-bodied Airbus or Boeing is around €458, which works out at around €3.40 per passenger.

Despite the slowdown in aviation, congestion is still a problem, especially in north-west Europe.

The average delay due to ‘air traffic flow management’ rose last year to two minutes and 20 seconds.

NO-SHOW

If you are travelling on a cheap ticket, expect to lose all your money if you fail to show up. You could try to reclaim the taxes, fees and charges that airlines are so quick to add but less hasty to subtract. However, many impose fees equal to or greater than the amount you can reclaim.

Travellers on ‘full-fare’ tickets can usually switch to another flight without penalty. But be warned that if you fail to show for your outbound flight, many airlines will automatically cancel the inbound leg.

OVERBOOKING

A splendid device. Typically, a handful of passengers will fail to turn up for a flight without a penalty, as they book themselves on several flights and take whichever turns out to be the most convenient.

Clearly, airlines would lose revenue unless they accepted more reservations than there are seats. Sometimes they guess wrong and everyone turns up. This is not only embarrassing, it is also expensive — the European Commission lays down rules for denied boarding compensation. The other weapon at the airlines' disposal is to enforce the latest check-in time, so if you arrive late, you forfeit all your rights.

Overbooking is one reason why airlines are often less than keen to give you a pre-assigned seat.

PRE-ASSIGNED SEATS

When you book theatre tickets, you expect to be told where you are sitting. Surely airline passengers can expect the same courtesy? No. On many long-haul flights, seats may be allocated upon booking, but the airline will always reserve the right to change them. And if you have any special requirements, such as extra leg room, you may have to wait to try your luck at the airport — or pay extra for the privilege.

On Aer Lingus, you can choose your seat in advance on transatlantic flights with no fee, but the airline normally charges €12 for pre-booked flights on other routes. British Airways passengers, even on short-haul flights, can pick a seat online 24 hours in advance — including those prized exit rows.

“We're giving control back to customers,” says BA. If you are travelling in a couple and want to maximise the chances of having a row of three seats to yourselves, book a window and an aisle seat; unless the plane is totally full, it is unlikely that the middle one will be filled.

QANTAS

The Australian airline that began as Queensland And Northern Territory Aerial Services is probably the most widely misspelt carrier in the world (plenty of people add a ‘u’ as the second letter).

It was established in Brisbane in 1920, and is today one of only three aircraft to fly the Airbus A380 ‘Superjumbo’. Qantas (qantas.com) has installed only 450 seats on the Superjumbo, compared with 471 on Singapore Airlines and 489 on Emirates.

When Air France starts flying the A380 between Paris and New York later this year, it will pack in 538.

On the Qantas aircraft, the website seatguru.com recommends 71D, 79B-79K, 80A and 80K as the best seats in economy class.

RYANAIR

An airline that attracts passengers and opprobrium in staggering quantities, Ryanair now qualifies as “the world's favourite airline” in accordance with British Airways' definition of the carrier that flies more people internationally than any other.

This month, for the first time, a single airline will offer more than 10pc of all the available intra- European seats. Yes, it's Ryanair, way ahead of Lufthansa, Air France and British Airways, not to mention easyJet.

“If there was any alternative to flying on Ryanair, I'd take it,” said the broadcaster David Dimbleby earlier this summer when he was caught up in the ground-handling snarl-up at Stansted. But the airline's chief executive, Michael O'Leary, appears to be positioning himself for an upgrade to sainthood. “I am beloved across the industry and across the world,” he told me recently.

SLOTS

This refers to permission to land and take off at specific times at a particular airport.

A few British airports are ‘slot-constrained’, with more demand than supply, notably Heathrow — which is full almost all of the time, from the first arrivals in the small hours to the last departures late at night.

The two strips of concrete west of London constitute the most valuable real-estate any- where on the planet, and 99pc of available slots are taken up. About the only ones that aren't used are for unappetising lateevening flights or the odd space at weekends.

‘Slots’ also refers tactically to the exact minute a plane is permitted to take off by air-traffic controllers (see Maastricht). Pilots are averse to losing this slot, which is why, on boarding, you may be urged to sit down and get strapped in very quickly.

TRANSATLANTIC AVIATION

Protectionism is rife around the world, with governments limiting international flights to protect inefficient airlines.

Europe and the US are well ahead of the pack in having reasonably free and open markets, and last year the North Atlantic air lanes were liberalised.

But apart from lots of carriers moving US flights from Gatwick to Heathrow, not much has happened to benefit travellers; Northwest's link to Seattle and Air France's to Los Angeles did not last long.

And since the collapse of Zoom last August, there are actually fewer US destinations than before ‘Open skies’.

UPGRADES

If you want to fly in business class, buy a businessclass ticket. Next best option: marry someone who works for an airline (but one with a business-class cabin, silly — not Ryanair).

Failing that, demonstrate your loyalty to an airline by signing up for their frequent- flyer programme. If they have to upgrade people because the economy cabin is overbooked, that's where they will look first. Or fly on your birthday: before Swissair went bust, I was given an upgrade from Heathrow to Zurich on December 25 (which, incidentally, is the least stressful day to fly; Easter Sunday is next best).

VELOCITY

Not all jet aircraft are equally fast. On the Heathrow-Hong Kong route, three aircraft are scheduled to take off between 10.20pm and 10.35pm each evening.

First off is a British Airways’ Boeing 777, which is scheduled to take 12 hours.

Next is a Virgin Atlantic Airbus A340, which takes 20 minutes longer.

Finally, a Cathay Pacific 747 — which overtakes the Virgin plane and nearly catches up with BA — takes only 11 hours and 50 minutes.

WORLD CUP

Every four years, football fans distort the flying patterns of the world.

Book a British Airways flight from Heathrow to Johannesburg on May 8, 2010, for a month, and you will pay around €800. Try it a month later and the price rises to around €1,150.

Any big sporting event puts huge pressure on airline seats, which the airlines take advantage of by raising fares. A reader, Nick Mount, has just got in touch to say: “We are flying to Durban in June 2010. The flights have doubled in price. Is this legal [yes] and is there anyway of getting a flight at the usual price? [no].”

X-RAY

Not the wellknown camp in Guantanamo, but the scanner that examines your luggage to assess how much of a threat to the aircraft your possessions pose.

Later this year, more sophisticated scanners will start to appear that can detect the potential of liquids to cause explosions, and gives hope that the present 100ml limit on bottles may be relaxed. Others say that it is ridiculous to devote so much time, money and energy on searching passengers who pose no threat. They advocate screening passengers based on booking patterns and — very controversially — age, nationality and even appearance.

Some campaigners say that security staff already disproportionately select Asian men for extra attention.

Profiling already happens in other walks of life. The revenue protection officials at my local railway station make no attempt to hide the most obvious profiling of people they regard as most likely to be travelling without a ticket: young men of any colour.

YECONOMY CLASS

Of course it is. You probably also knew that C is business class (predominantly short-haul), J is long-haul business class and F is first class. But these are merely the cabin classes.

Your electronic ticket is likely to show a different letter entirely.

B, G, H, K to O inclusive, Q, S and T to X are used to refer to discount economy categories, all of whom sit in the economy cabin (unless they have friends in high places — see upgrades). A colleague flying to Toronto was delighted to see the newspaper had booked her in B class, which she took to be business, only to find herself at the back of the plane.

The top class, by the way, is not A but R, formerly used exclusively for Concorde but now for first-class suites on the Airbus A380.

ZULU

Pilot-speak for Greenwich Mean Time, the clock by which all aviation is governed.