CHICAGO -- It was supposed to be a cheap and easy way to steal sales from Airbus' hulking A380 double-decker jet.

Boeing would update its decades-old 747 jumbo for the large freighter market, which Airbus was ignoring, with cutting-edge technology borrowed from the 787 Dreamliner, including new, powerful, fuel-efficient engines.

But five years later, Boeing is struggling to resolve design and technical issues with the 747-8 program that are partially a byproduct of the Dreamliner's production woes. Like the 787, the jumbo jet is late, badly over budget and almost certainly headed for another costly delay, analysts said.

The string of missed deadlines, supply-chain mishaps and design flaws that have plagued the two aircraft have tarnished Boeing's reputation for top-flight engineering and called into question its decision to rely on suppliers to design and build portions of the jets.

As Boeing works to correct those problems, Wall Street increasingly worries about the drain the two jets are placing on Boeing's cash and engineering resources. Analysts want assurance that Boeing won't see another debacle when it updates two other popular models this decade -- its 737 narrow-body jets and long-range 777 twin-aisle planes.

"If they don't learn from their mistakes, they're really in trouble," said Paul Nisbet, aerospace analyst and president of JSA Research.

The Dreamliner and jumbo jets have progressed significantly since the panicky days of 2008, when Boeing drew engineers from across the company to rescue the 787.

But as the planes undergo rigorous flight testing needed to gain certification from federal authorities, technical issues still are coming to light, especially on the 747-8. Boeing concedes that it is unlikely that the process will be completed this fall, as it had predicted.

On Aug. 27, Boeing said the 787's first delivery would be delayed to early 2011, as analysts expected, and it also shook up the 747's management team.

Program head Mohammad Yahyavi was placed on "special assignment," while Pat Shanahan added oversight of the 747 program to his portfolio of responsibilities as vice president and general manager of Boeing's airplane programs.

There have been persistent rumblings of problems with the 747, analysts said, even though the freighter version of the plane has achieved milestones during flight testing, like last month's successful takeoff with a million-pound payload, the heaviest ever for a Boeing jetliner.

Boeing spokesman Tim Bader said the company is trying to resolve two problems unearthed during test flights that involve vibration in the 747's wings and the inboard aileron actuator, which moves the flaps that control rolling and banking.

Union leaders said Boeing's engineers still are slogging through a host of technical issues, ranging from small to potentially troubling, many of which originated with contractors. One cause for concern is whether ducts that feed compressed air from the engines into the plane's cabin pressure system will meet certification standards, sources said.