1.   American aviation safety experts have arrived to help in the investigation.

2.   American aviation investigators say they do not know whether the explanation given by the pilot, which was first reported Friday in The Los Angeles Times, is true.

3.   A similar decision was made by the National Aeronautic Association, which keeps American aviation records.

4.   But when American aviation experts arrived in Manila to help in the investigation, they found no evidence of any attack and no evidence of an obvious mechanical cause.

5.   It urged FBI officials to check the visas of foreigners at American aviation academies.

6.   It was the second threat to American aviation in two months that government officials viewed as credible enough to warrant immediate action.

7.   Some senators said the new national force was needed to bring American aviation security up to the standards of Israel and Europe.

8.   The document warned that followers of bin Laden were training in American aviation schools.

9.   The task, ultimately, fell to Gen. Jimmy Doolittle, an American aviation hero.

10.   These have been difficult days for Americans who fly and for American aviation.