The American directive, which has come into immediate effect, applies to all flights using American air space. An estimated 800 to 1,000 passenger flights a day could potentially be required to use sky marshals.
According to the regulation, 'where necessary' foreign carriers 'will now be required to place armed, trained law enforcement officers on designated flights as an added protective measure'.
Armed marshals disguised as passengers are already deployed on thousands of US flights each week.
Several countries, including Germany and Canada, already use armed guards, while others are considering, or in the process of implementing, the measure.
I've been told that the only truly significant plane-related security improvements since 9/11 were armoring the cockpit door and training pilots to dump fuel and drop the plane when an assault is underway. These changes don't directly reduce the risk of a takeover, but they make the plane much less useful as a weapon. So they reduce the motivation for seizing a plane, with indirectly reduces the risk of a takeover.
The abrupt request for air marshalls on international flight causes me to wonder if those changes were made only for US pilots. If that's true, then someone senior ought to lose their job. The training and armored door mandate should have been obligatory for all flights entering North American airspace since early 2002. I hope they were.