http://www.aa.com/i18n/travelInforma...nAllowance.jsp as of today says:
Carry-on roller board bags, duffle bags, large backpacks, or other personal items that don't fit in the overhead bins or under the seat must be checked at the gate and placed in the cargo compartment on American Eagle aircraft.
Regardless of what the above rule says, regardless of whether the bag fits or not, the gate agent will generally try to make you "
valet check" any upright roller, even if it is 17".
Valet check means that the bag is delivered back to you at the arriving gate, not at the belt.