The National Transportation Safety Board's March 24 readout put a number on the LaGuardia collision's critical interval. One of only two air traffic controllers on duty cleared a Port Authority fire truck to cross a runway twelve seconds before the Air Canada Express flight touched down, leaving no margin for either vehicle to avoid impact. [1] Both pilots were killed.

The NTSB timeline, reviewed from the cockpit voice recorder, runs this way: twenty-five seconds before the crash, the fire truck requested to cross the runway where the plane had already been cleared to land almost two minutes earlier. The controller cleared the truck five seconds after the request, when the plane was roughly 100 feet from the ground. Nine seconds before impact the tower told the fire truck to stop — a second before the landing gear touched down. [1] The airport's runway-status lights appear to have been functioning, designed to turn red automatically when a runway is occupied. [2]

The dormant infrastructure-safety thread reactivates on the twelve-second datum because that number, unlike the redacted staffing minimum and the unresolved ASDE-X behavior questions, is legible reform language. Overnight staffing of two controllers at a major hub is "normal" by current FAA practice. Aviation-safety analysts interviewed after the crash divided on whether that norm is defensible given the 12-second window the tape captured. What the NTSB produces next — probable cause, contributing factors, recommendations — is the test. The thread was dormant because no new datum was public. This one is.

-- NORA WHITFIELD, Chicago