Airlines keep chipping away at perks to maximise profits. Of late, US carriers have been tightening air-mile rules. The cheapest economy fares may earn nothing unless the ticket is bought with a co-branded credit card. Rewards now go mainly to high-spending loyal customers, not economy passengers. In Europe, hardcore low-budget airlines are refining the business of discomfort. They still push the idea of ‘vertical’ saddle seats, discussed since 2010, promising 63 percent more passengers if regulators ever approve it. Almost everything carries a cost: sitting with family, choosing seats, printing a boarding pass, bringing an oversized cabin bag, checking a bag or even a bottle of water. Indian airlines are learning. Revenue ideas travel well.