| Answer | Crossword Clue |
|---|---|
| stackup | planes circling an airport waiting to land |
| stackups | STACKUP, planes circling an airport waiting to land |
| stackup | group of airplanes circling over an airport awaiting their turns to land |
| stack | to control the flight patterns of airplanes waiting to land at an airport so that each circles at a designated altitude |
| clearances | Permission for an aircraft to take off or land at an airport |
| clearance | Permission for an aircraft to take off or land at an airport |
| thresholds | The beginning of an airport runway on which an aircraft is attempting to land |
