Frontier and Southwest carry-on limits near TSA scanner clearance

Travelers carrying the largest bags allowed in the cabin on Frontier Airlines and Southwest Airlines face a tight fit at security checkpoints, where the Transportation Security Administration is installing computed tomography scanners with smaller openings than the bags the carriers permit.

Both airlines set their cabin bag limit at 24 by 16 by 10 inches, or 61 by 41 by 25 centimeters. The CT scanner tunnels measure about 24.5 inches wide by 16.5 inches high, or 62 by 42 centimeters.

On paper a maximum-size bag passes. In practice, the two dimensions that matter at the scanner entrance leave roughly half an inch of clearance, so a bag that meets the airline's stated limit may still be difficult to feed into the machine.

The constraint applies to passengers flying with the largest permitted carry-ons rather than to the bulk of cabin luggage, which is smaller. The TSA is rolling out the CT scanners as part of its checkpoint equipment programme.