An investigator looking into a jet crash that killed 25 people Sunday discounted the possibility that a bird caused the accident, despite the discovery of feathers stuck to a wing of the plane.

One day after the crash of the United jet, other possible causes under investigation included pilot error, low fuel supply and wind shear, when wind speed reverses across a plane's wings and causes it to drop like a rock."At this point it is a very wide-open investigation," John K. Lauber, head of the National Transportation Safety Board team investigating the accident, said Monday.

"There is nothing we would rule out at this point and nothing we would rule in."

Feathers were found on small pieces of wing, the investigator said. Collisions with birds or instances in which birds were sucked into jet engines have caused plane crashes, but Lauber said that was unlikely in this case.