ENGINEERS at Boeing’s aircraft plant in Seattle are working on a modification to the latest model of the ubiquitous 747 jumbo jet. It’s not a new wing, bigger fuel tanks or any of the other usual updates to commercial airliners.

It is, although Boeing executives would blanch at the description, a set of servants’ quarters. All seven of the super-wealthy individuals and governments that have ordered luxury versions of the new jumbo — a lengthened, re-engined version called the 747-8 — have asked Boeing to exploit an unused area on the big plane between the cabin ceiling and fuselage.

The gap is just large enough to stand up in and runs more than half the length of the aircraft. Engineers have devised a pod that slots into the space, kitted out with bunk beds or seating.

“We’re going to make it basic for the specification of the VIP version of the aircraft,” said Steven Hill, president of Boeing Business Jets. Not that the head of state or Saudi prince who owns the aircraft will see inside. “I don’t think it’s likely to be the principal’s domain,” Hill said.

If the idea of installing servants’ quarters on your personal jumbo sounds excessive, you have not been keeping tabs on the latest developments in the business-jet market. America is headed for recession, oil prices are going through the roof and the credit crunch has cut down big financial institutions. In the world of corporate aircraft, however, it is party time.

Sales are at record levels, having more than doubled in the past five years, and show no signs of slowing. Plane makers have a backlog of orders that would keep them working flat out for five years, even if orders stopped tomorrow. And ever more luxurious, bigger and faster models — including a son-of-Concorde supersonic corporate express — are being launched almost every month. Rolls-Royce, the sober-minded FTSE 100 aero-engine maker, reckons the business is worth $715 billion (£361 billion) over the next two decades.

Ebace, a mini-Farnborough air show for the business-jet fraternity held in Geneva last week, offered a glimpse of just how hot the market has become. Multi-billion-dollar deals were two a penny.

Two were particularly eye-catching. Xojet, a California-based business-aviation company, made light of the credit crisis, raising £2.5 billion to fund expansion, drawing in investors from America and the Gulf.

A few hours later, Maz Aviation, a Saudi Arabian operator of luxury jets, made a splash. It bought six VIP versions of the Airbus A350, a wide-bodied airliner not yet off the drawing board and unlikely to enter service until 2014 at the earliest. The deal was worth $1.5 billion.

According to industry sources, Maz placed the order because it did not want to miss out on what it thought would be a highly prized item in five years’ time.

An Airbus source said: “They have seen what is happening with other planes right now, where you have long waiting times for delivery. They thought they should get in first.”

With such big money being wagered on a luxury item, the business-jet industry would seem to be in the midst of the biggest bubble since the dotcom boom. If the world economy continues to falter, surely there will be an almighty reckoning for today’s high-flyers?

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