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Feb 28 (Reuters) - Boeing said on Wednesday its stretched 747-8 jumbo jet would be able to meet pledges contained in its original catalogue by 2014 after shortfalls in performance affected the earliest models.
With new engines and wings, the 747-8 is the largest airliner built in the United States and is designed to carry 467 people or 134 tonnes of cargo when delivered as a freighter.
But early examples of the first ever stretched version of the iconic jumbo have been described as overweight and the General Electric GEnX engines as too fuel-thirsty.
"The planes delivered so far have been performing very well in service, about 1 percent better than we thought," said Boeing spokesman Jim Proulx.
"They are giving double-digit gains in fuel burn (compared with the models they replace) and are on a path to getting back to catalogue commitments in 2014."
He was speaking shortly after Boeing delivered its first 747-8 Intercontinental passenger version to a secret VIP customer, thought by industry insiders to be the state of Qatar.
Boeing has delivered 10 747-8 freighters out of 70 on order.
The company recently moved to reassure buyers by upgrading the maximum take-off weight by 6 tonnes last month.
The move was officially pegged to the discovery during flight tests that the plane was stronger and more efficient than expected. But it prompted speculation that the decision also masked an increase in the structural weight of the aircraft.
Weight is a constant worry of aircraft manufacturers.
Industry sources familiar with the 747-8 say it has accumulated some 8-11 tonnes of excess weight in development.
The rival Airbus A380 was around six tonnes overweight when it entered service in 2007, according to major customers.
Boeing confirmed that the 747-8 had been fighting some flab, something that often happens in early production as engineers tinker with the plane to fix teething problems.
"As with all new airplanes, we have certainly had our challenges with weight. We are working on reducing these and improving the capabilities," Boeing Commercial Airplanes marketing vice-president Randy Tinseth told Reuters recently.
Weight translates into money because when an aircraft is heavier than planned, operators have to reduce the amount of payload they can carry or else reduce the distance flown.
In the case of the 747-8, Boeing and engine maker GE have been wrestling with both weight and sub-par performance in the engines, the latter prompting launch customer Cargolux to refuse initial delivery of the first aircraft last September.
Boeing says the new raked wing helps compensate for this.
GE has said it is working on improving the GEnX performance.
"The early deliveries are short of our commitment on fuel burn" but "with the improvements we have committed on the airplane, we will do that" (meet performance goals), 747-8 vice president and general manager Elizabeth Lund said on Wednesday.