One thing that's alluded to in this thread, but where I've heard people getting dinged, is the 62" linear measurement limit (L" + H" + W" <62"). Above that you CAN get charged $200+ for oversized luggage, even if below the 50lb weight limit.
Oversized luggage measurements
US DOMESTIC AIRLINES
AIRLINE | SIZE IN INCHES | WEIGHT/LBS |
---|
Allegiant Air | 80 Linear Inches | 50 Pounds |
Alaska Airlines | 62 Linear Inches | 50 Pounds |
American Airlines | 62 Linear Inches | 50 Pounds |
Delta Airlines | 62 Linear Inches | 50 Pounds |
Frontier Airlines | 62 Linear Inches | 40 Pounds |
Hawaiian Airlines | 62 Linear Inches | 50 Pounds |
JetBlue Airways | 62 Linear Inches | 50 Pounds |
Southwest Airlines | 62 Linear Inches | 50 Pounds |
Spirit Airlines | 62 Linear Inches | 40 Pounds |
Sun Country Airlines | 62 Linear Inches | 50 Pounds |
United Airlines | 62 Linear Inches | 50 Pounds |
Seems to vary by airlines how much the 62" rule is enforced, based on what I've heard/seen (Alaska and Southwest seem to be pretty cool about it, United and American less so, and Delta somewhere in between).
For example, the SKB double bow case (I have one), actually falls into oversized luggage, and I should have to pay a fee each way. My bypass has been to use miles to upgrade, where the free bag included increases the likelihood of the gate agent looking the other way.
Just an FYI...