Southwest doesn't charge for the first two checked bags, but it has added and increased other fees such as priority boarding recently.

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Passengers can opt for priority boarding either by paying extra for their ticket (as with Ryanair) or by joining easyJet's loyalty scheme.

ECONOMIST: Budget airlines

Frequent flyers would have to give up their priority boarding positions.

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This is why budget airline Ryanair, notorious for offering ultra-cheap fares around Europe, also charges for reserved seating, priority boarding, bringing infants on board, carrying musical instruments or sports equipment and re-issuing boarding passes.

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Priority boarding is also a big draw, because Southwest's chaotic no-assigned-seats system can be a turnoff for travellers unwilling to push to the front of the line or throw a few elbows for a window (or aisle) seat.

ECONOMIST: Business travel

The bundle combined the priority-boarding package it currently sells with its Economy Plus extra-legroom seating, two checked bags and additional frequent-flier miles.

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Joyce said the new partnership would benefit its frequent flyers in particular, with the airlines offering reciprocal access to tier status benefits, including end-to-end recognition of customers, lounge access and priority check-in and boarding.

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The legal requirement for passports and boarding cards to be checked by airline officials before boarding remains, but miSense passengers are given priority.

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