A week ago I asked: Where were all the helicopters? Tuesday, the Wall Street Journal reported that "[N]o piece of equipment was more necessary than helicopters. But in the first 48 hours after the levees were breached, the shortage of helicopters became acute," and came up with this partial answer:
Because of worries that terrorists could take advantage of such chaos, FEMA now must abide by post-9/11 security procedures, such as putting air marshals on flights. That meant stranded residents couldn't be evacuated from the New Orleans airport until FEMA had rounded up dozens of Transportation Security Administration screeners and more than 50 federal air marshals. Inadequate power prevented officials from firing up X-ray machines and metal detectors until the government decided evacuees could be searched manually.
UPDATE: My eyes, though maybe not yours, glazed over at the "airport" part of the above quote, which makes the air marshal thing less of an overall factor in the helicoptering of Katrina, though no less stupid. Also, the article points to other factors, some of them contradictory, none of them wholly convincing (to me) one way or another.