1.   A rudder malfunction is suspected, but early indications are that this crash did not occur in similar circumstances.

2.   But the safety board may have identified two mechanisms by which a single failure could cause a rudder malfunction.

3.   He did, however, acknowledge that there is at least one recent incident of a rudder malfunction that experts cannot explain.

4.   If both crashes were caused by a rudder problem, the odds of another rudder malfunction is, quite literally, about one in a million.

5.   If the investigation is building a circumstantial case for a rudder malfunction, a lot of work remains.

6.   Investigators have not been able to determine a probable cause of either crash, but suspect rudder malfunctions contributed to both.

7.   Safety investigators have long suspected that unusual rudder malfunctions were responsible for the crashes.

8.   The board asked Boeing to provide a list of incidents involving loss of lateral control over the planes, which would include rudder malfunctions.

9.   Among the areas to be examined is the possibility of a rudder malfunction.

10.   It was not clear, however, that the impurities contributed to the rudder malfunction, said Michael Benson, spokesman for the National Transportation Safety Board.