Airlines want to keep their passengers better informed from the moment they leave home, going beyond simple flight delay information to try to ease travel stresses and ensure customer loyalty.

The industry must offer a more seamless journey for travellers, especially with the number of people flying expected to double from an annual level of 3.5 billion in 20 years, delegates at this week's World Passenger Symposium in Hamburg said.

While travelling can never be entirely stress-free, improving the flow of information and providing automatic rebooking could help ease frustrations when delays do occur.

Giving passengers information on everything from security and immigration waiting times to public transport delays or traffic jams could also help airlines to retain customers in a highly competitive market.

Philippe Der Arslanian, vice president digital and merchandising at travel technology company Amadeus IT, said happier passengers would be more open to making additional purchases while travelling.

"Upsell, don't upset," he told the conference.

Airlines should also communicate more information on delays or route changes so that services such as car hire and hotels can be rebooked automatically, without the passenger having to fret, said Tony Tyler, director general of the International Air Transport Association (IATA).

In an example of an effort to make journeys easier, Lufthansa on Friday said it was teaming up with Postbus to sell tickets for bus routes to Munich airport as part of the flight booking.

If the bus is delayed, then passengers who booked with Lufthansa will be automatically booked on to the next flight.

Delegates also expressed hope that technology will facilitate smoother, faster journeys through airports. For example, if bags could be scanned more efficiently, that would avoid the need for people to unpack and then repack their hand luggage during security checks.

"It's about things happening smoothly without interrupting the flow... where everything gets out of the way of the customer," Tyler told journalists.