As federal investigators convene a weeklong hearing in Pittsburgh today, they have little progress to report on the crash of USAir Flight 427 in September.
After five months of investigating a plane crash, the National Transportation Safety Board usually comes up with something telling.
That hasn't happened in the case of the Sept. 28 crash.
The Boeing 737 jetliner rolled suddenly to the left and plunged 5,000 feet to the ground as it approached Pittsburgh International Airport, killing all 132 people on board.
The flight data recorder recovered from the wreckage was an older model that provided only 17 channels of information on the plane's performance, compared to the approximately 100 available from the more modern recorder recovered from the crash of a commuter plane in Indiana last Halloween.
The 737, slamming nose first into the ground at more than 300 mph, shattered into fragments on impact, leaving investigators few pieces big enough to provide meaningful information.
Because the jetliner crashed near dusk in a rural area, there were few witnesses on the ground.
The only apparently similar accident was the crash of a United Airlines 737 in Colorado Springs, Colo., in 1991, and the cause of that remains a mystery too.
What it all means is that this time the principal objective of the hearing will be to question aviation experts in the hope that the exchange of information, ideas and theories will produce something new.
"We hope to get detailed factual information in areas in which we haven't had information before," said Mike Benson, an NTSB spokesman.
"We'll be talking to Boeing, USAir, NASA, the FAA -- people who have played a role in developing the 737 and its components . . . people who have flown the plane," he said.
When it comes to the big question -- why did Flight 427 crash? -- the NTSB hasn't ruled out anything, but the theories proposed thus far have failed to prove out.
They have included a bomb and suggestions that one of the plane's two engines may have reversed.
Other theories remain viable but unproven, including one concerning the rudder.
Aviation experts have noted that a sudden, full deflection of the rudder -- the hinged slab on the vertical part of the tail that helps a plane turn left or right -- could have caused Flight 427's sudden roll to the right and noseward plunge.
The rudder was suspect in the Colorado Springs crash, and exhaustive tests have been performed in an effort to learn whether Flight's 427's rudder systems performed properly.