Crossword puzzle clue "u s threat level at airports"

U.S. threat level at airports

Homeland Security threat level represented by "yellow"

Low-level pollution or high-level protection

Warning sign at a train station's food court? (NOTE: The original sign, without my additions, actually exists. It's in Grand Central Terminal in NYC, on the lower level — the food court level. The sig

Class, level or class level

Management level or theater level

Dep. opposite, at airports

Company started in 1946 at the Detroit and Miami airports