Casing the joint?

Daveed Gartenstein-Ross wonders whether several false alarms, in which airline passengers engaged in "suspicious" behavior, weren't really practice runs.

TWELVE PASSENGERS ON Northwest Airlines Flight 42, which departed Amsterdam for Mumbai on August 23, quickly aroused the crew's suspicions. Eyewitnesses reported that the 12 passengers, who were of South Asian descent, attempted to use mobile phones and pass them back and forth as the flight took off. Compounding that suspicious behavior, some of the men began walking in the aisles before the plane's seatbelt signs were off. The flight was escorted back to Dutch airspace by F-16 fighters and the passengers were arrested, but Dutch prosecutors announced the next day that "they found no evidence of a terrorist threat."

This dramatic incident comes amid what has generally been described as a rash of false alarms following the August 10 revelation of a foiled transatlantic air terror plot. Since then, at least 20 public incidents involving airline security have been reported in the United States and Europe. Recent events include a September 1 AirTran flight to San Francisco being diverted after a passenger was seen sniffing a substance in a bag, an August 29 US Airways flight from Philadelphia to Houston being diverted after a "threatening note" prompted a bomb scare, and an August 25 US Airways jet being diverted after a disruptive passenger pushed a flight attendant. The commonly accepted explanation for this spike in incidents is that airline crews and passengers are on a hair trigger. But there may also be casings and dry runs occurring, and it's difficult for an open society to guard against these exercises.

THE TRANSATLANTIC AIR PLOT that was disrupted in early August provides the latest evidence of how terrorists probe airline defenses. Intelligence sources report that at least one of the plotters took several flights between Britain and the United States with only one plausible purpose: probing weaknesses in airline security.