After nearly twenty years of development -- and $19 billion -- it's still unclear whether a controversial, ultra-pricey, tilt-rotor aircraft "can perform all the maneuvers that several pilots [say] are necessary in combat," the Ft. Worth Star-Telegram reports.

For an eternity, it seems, the Pentagon has been pushing the V-22 Osprey as "twice as fast, three times the payload capacity, and six times the range" of traditional helicopters. But the advantages of this "revolutionary" machine have been greatly exaggerated, critics say. (The Pentagon disputes this, of course.) "The V-22 might have only one significant performance advantage over helicopters: speed," according to the paper. "Important mechanical components continue to fail, reinforcing long-standing concerns about reliability and maintenance costs."

During recent tests, pilots weren't allowed to take the V-22 on "extreme maneuvers" like sharp banks and U-turns. Why? Because "program officials feared the maneuvers would damage the aircraft," according to the Star-Telegram.

Back in April 2000, a V-22 crashed in Marana, Ariz., killing 19 Marines. It's one of several major mishaps that've happened during the Osprey's two decades of testing.

Some veteran pilots and aviation scientists said the accident exposed an inability in the V-22 to descend rapidly and abruptly change directions, key requirements for combat aircraft. Aerodynamic experts advising Christie and his predecessor, Philip Coyle, argued for additional tests. The Government Accountability Office, a government watchdog agency, called for "realistic" tests.

Some testing was done. But a series involving specific, sharp defensive maneuvers was skipped after Bell engineers warned that it would severely damage the rotors, according to a source within the testing program who asked not to be identified for fear of losing his job.