Engineers at Airbus and Boeing are racing against the clock to carry out long-awaited test flights and shore up ventures worth billions of dollars.

Boeing says its next-generation 787 Dreamliner passenger jet will fly this month, and Airbus plans a maiden sortie for its A400M military transporter as early as next week. Both have set themselves a year-end deadline to end harrowing birth pangs.

The sleek jet and rugged propeller plane could not look less like runners in the same race, but each is nearly ready to prove its worth to investors and buyers after technical problems.

After millions of hours of design work, there is little suspense over whether either aircraft will actually fly.

But getting them aloft means more than pride for both companies after the development delays hit share prices and triggered penalty clauses and management turmoil.

Flight test is all about discovery. We have a high degree of confidence in the design, but you always want to do that final check which is flight test to make sure there are no surprises, Dennis O'Donoghue, Boeing vice president in charge of flight testing, told Reuters in a recent interview.

I don't care what program it is, you usually find some surprise somewhere. The experienced folks take it in stride.

Airbus and Boeing are racing the calendar rather than each other, but Irish bookmaker Paddy Power is inviting punters to bet a few euros on who will get their plane in the air first.

Yet the industrial gamble stacks up in billions of dollars.

Boeing's is expected to be the more low-key event and the company declines to say who will be in Seattle to witness it.

Analysts say a good test program could help to halt a run of cancellations, whereas further delays would give Airbus more time to close the gap with its rival A350, due next decade.

Airbus, on the other hand, is expected to fly the A400M in front of an A-list audience in Seville headed by the King of Spain, a trained pilot who attended a factory roll-out in 2008.

The reason is the plane's future is uncertain after cost overruns cast doubt over the 20 billion euro project. A successful flight is seen as crucial as seven NATO nations discuss whether to keep Europe's largest arms contract, also with an end-year deadline.

Those talks will determine whether the A400M goes to war as a beast of burden or the nearest museum as a white elephant.

Experts say a successful first flight may provide some cover for an awkward political decision to bail out Airbus parent EADS over some of the cost overruns, a move Germany opposes.

But at least one military chief is said to be so irritated by delays he has cut down attendance at the event, citing costs.

PAS DE DEUX

As for the planes, they will rarely be mentioned in the same breath once the coincidental pas de deux of first flights is over, but they will be on the same page of engineering history.

The 787 is mainly built of advanced new weight-saving materials that are lighter than aluminum to save fuel and the A400M's wings are made out of similar carbon-fiber material. Each plane is powered by new engines that themselves represent big industrial bets -- van-sized General Electric or Rolls-Royce powerplants for the 787 and the West's largest ever turbo props on the four-engine A400M. Each aircraft aims for billions of dollars in exports and targets a new mid-sized market in their respective spheres.

The two main variants of the 787 are designed to carry 210-290 people further on two engines than the typical 416-seat Boeing 747-400 jumbo jet does on four, and in greater comfort.

With a 37-tonne payload, the A400M is aiming for a niche between the Lockheed Martin C-130 prop plane, a 1950s workhorse able to lift 21 tonnes, and the 75-tonne Boeing C-17 jet.

Airbus is seen likely to need non-European sales to try to break even on the A400M, even after any political deal on costs, and the first flight is expected to kickstart a new sales drive.

All that is now missing is the traditional muscular identity for a new war machine. Airbus has put out feelers for a nickname to pitch it against the C-130 Hercules and C-17 Globemaster.

(Editing by John Stonestreet)