FAR 25.1001 (If i remember correctly) Fuel Jettison System: states that an aircraft must be able to achieve the required approach/landing climb gradients within 15 minutes of takeoff.
All of our landing field length limit charts have weights much greater than the MTOW.
We stipulate that overweight landings are not permitted for commercial reasons, in all other cases crew must assess if they can satisfy the field length limit weights and approach/landing climb limits and follow the appropriate overweight landing checklist.
Mutt