[pompelmous]

If the passengers and cargo are screened and there are marshals on board what good is done by canceling the flight?

[FairOpinion]

Depends on the threat.

"Another major concern was the possibility terrorists with shoulder-fired missiles might lie in wait along certain flight paths, the newspaper reported."

==

This was a comment re. the cancellations over the holidays, but I think it's still a valid concern. This type of threat would explain the cancellations.

http://www.thestar.com/NASApp/cs/ContentServer?pagename=thestar/Layout/Article_Type1&c=Article&cid=1073086208968&call_pageid=968332188854&col=968350060724