From aa.com:
"
How Much Can I Carry On?
Dimensional Inches Diagram You can carry on one bag plus one personal item per passenger as long as:
# They weigh no more than 40 lbs/18 kgs
# The bag is no more than 45 inches and the personal item is no more than 36 inches when you add the length + width + height so that it fits in an overhead bin or under the seat
Personal item - includes: backpack purse, briefcase, laptop OR a similar item such as book bag or tote that does not exceed 36 inches( length+width+height) and fits under the seat.
Additional items that will be allowed above and beyond the restrictions listed above include:
# Outerwear such as coats/wraps/hats
# Book or newspaper
# Small bag of food to eat on the flight - see guidelines for liquids
# Approved safety seat for lap or ticketed child
# Umbrella stroller for lap or ticketed child
# Diaper bag for lap or ticketed child
# Assistive devices for passengers such as wheelchairs, walkers and CPAP machines
# Therapeutic oxygen provided by the airline"
Nothing about camera bags (as opposed to a camera.) Nonetheless, my Lowe camera bag and max size carry-on have accompanied me on many a flight. It has only been taken from me a very few times - notably at LHR by BA, and once by UA at LAX (that was a Pelikan locking case with u/w video equipment, which had been allowed as my personal item by FJ, UA etc.
)
Be prepared to quickly scavenge your carry-on for any valuable items you can put in your camera bag, then you will be prepared (but
probably not bothered.) And remember "stored under your seat" in NGBC means you wil lnot be able to stretch out and sleep in the reclined position, and "under your seat" will not be allowed in bulkhead rows in NGBC on takeoff and landing because they never got the new seats STCd for it.