Why do airlines love the Boeing 737 Max? In a word: money.

This is a plane that promised to cut fuel and maintenance bills, fly further and cram in more passengers – manna to airline executives and shareholders.

More than 5,000 of the new Max planes have been ordered, mostly the Max 8 iteration, allowing Boeing to maintain the 737’s historic chart-topping sales in the face of competition from the Airbus A320 family’s latest “neo” planes.

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While both manufacturers have launched more daring ventures with greater fanfare and mixed fortunes – Boeing’s 787 Dreamliner and the A380 superjumbo from Airbus – the Max was something else: a plane that didn’t rip up the model, but more or less matched the familiar, shorthaul workhorse. It replicated what airlines had already got, only better, lighter, and cheaper to fuel and maintain.

Buyers queued from every continent. In the UK, even the doomed Monarch ordered dozens, though the airline couldn’t quite hang on long enough to reap the forecasted annual savings of up to £3m a plane.

At a relatively affordable price, the Max – a single-aisle plane – had a flying range that opened up the possibility of using it on long-haul corridors traditionally the preserve of wide-body jetliners – an opportunity taken by Norwegian to fly new routes across the Atlantic.

For most, though, the ambition was purely economic. Speculation long surrounded Ryanair’s next move when it grabbed a deal as the launch customer for another Max version, the 200, which it dubbed the “game-changer”. It ruled out long-haul, but added more seats to the cabin. The Irish airline has 130 planes on order, the first 50 due to arrive between May and the summer. Michael O’Leary said the Max would cut his rock-bottom costs another 5%. And passengers could still be promised more comfort, legroom and nicer interiors.

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The stakes are now highest of course for Boeing, with a Max order book worth a nominal $600bn (£460bn). Airlines will have options elsewhere, but have planned growth and schedules on the delivery of this more fuel-efficient plane. The spectre of jet fuel prices that were twice as high a decade ago still lingers, and Boeing claim the Max runs on 14-20% less than the newest “next generation” 737s available before.

Should the 737 Max be grounded for long, conceivably more airlines could struggle and fares could rise. However, the price of operating a plane whose safety is in doubt could be incalculable.