The delivery of the 747-8 Intercontinental - Boeing's largest and most recognizable commercial airplane - caps a development delay of more than a year.

Boeing (BA.N), the world's second-largest plane-maker marked the milestone with an understated ceremony, keeping the media at arm's length to safeguard the identity of its customer, thought by industry insiders to be the state of Qatar.

"The 747 is the most iconic airplane in the world, and I know customers are going to love what we've done to enhance its performance," Jim Albaugh, president and chief executive of Boeing Commercial Airplanes, said in a statement.

"The Intercontinental is fast, efficient and quiet, offering real savings and a great flying experience," he said.

Boeing, which competes for orders with rival Airbus (EAD.PA), has taken 36 orders - nine from non-airline customers - for the aircraft, which lists at $332.9 million. The airplane is more than 12 months behind its initial delivery schedule and some experts say the order book is puny.

The Intercontinental is an elongated, upgraded version of the classic 747, which first flew more than 40 years ago. The 747 was the world's largest airplane until 2005, when Airbus unveiled its A380.

Only one A380 has been ordered by a wealthy individual, Saudi billionaire Prince Alwaleed bin Talal.

"The 747-8 has been slow to take off, and the success of the aircraft is still questionable given so few orders," said Alex Hamilton, an aerospace analyst and managing director at EarlyBirdCapital.

Boeing had delayed the delivery to 2012 from the fourth quarter of 2011. The company blamed delays in flight testing and the time required to incorporate flight-test driven changes.

A delay of a year or more is not unusual for modern commercial plane launches. Both Airbus' massive A380 and Boeing's carbon-composite 787 suffered multi-year delays.

Boeing does not identify VIP customers, but past buyers of customized planes have been multimillionaires and heads of state.

The first airline set to receive the plane is Germany's Deutsche Lufthansa AG (LHAG.DE), which has ordered 20. Boeing has not set a delivery date for Lufthansa's first Intercontinental.

EXTENSIVE MODIFICATIONS

VIP customers for planes as large as the 747 often request extensive modifications such as bedrooms or bathrooms to accommodate the special needs of the primary passengers and their entourages. These modifications typically are done outside of Boeing, but the company must sign off on the changes.

Boeing Business Jets president Steve Taylor, who was set to fly the airplane from Paine Field near Seattle, said it will spend about six months at Boeing's Wichita facility - the plant that modified Air Force One - for basic modifications.

From there it goes to a facility in Hamburg where it will spend two years receiving customer-specific outfitting like bedrooms, dining rooms and galleys, he said.

Taylor said the unnamed customer wants the new Intercontinental to be the "jewel of the sky."

The Intercontinental incorporates some of the technology of the lightweight, carbon-composite 787 Dreamliner. It can seat 467 passengers, 51 more than the current version of the 747, but fewer than the competing 525-seat A380.

By some estimates, the new 747-8 is 8 to 10 tonnes overweight. Elizabeth Lund, 747 program manager, acknowledged the plane is heavier than originally planned. But she said a redesigned wing makes up for the weight in terms of performance.

Additional weight can reduce the distance a plane can fly or the amount of cargo it can carry.

Boeing said the plane would meet the original performance commitments it made in the sale catalog by 2014.

The freighter version of the 747-8 was first delivered in October. Orders for the freighter have been strained by an economic downturn that has dampened cargo markets.

Boeing delivered its first 787 Dreamliner last year after three years of delays. The 787 represents a bigger leap in technology than the 747-8.

(Reporting by Bill Rigby in Seattle and Kyle Peterson in Chicago; Additional reporting by Tim Hepher in Paris; Editing by Maureen Bavdek, Tim Dobbyn and Carol Bishopric)

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