MAXIMUM LANDING WEIGHT LIMIT
Most people look to the MTOW (Maximum Takeoff Weight) when computing their takeoff weight limit. Actually, pilots need to know the maximum landing weight. On longer trips you can burn enough fuel to get down to the maximum landing weight by the time you land, but on shorter trips you may need to reduce the fuel quantity and/or passenger load.
For example, the DC-7C could carry up to 102 passengers. If we fill up the seats and carry a full fuel load of 46,950 lb, the takeoff weight will be 150,320 lbs. The DC-7C had a MTOW limit of 143,000 lbs, so we are 7,320 lbs overweight. If we need all that fuel for a very long flight, we will have to bump 30% of the passengers. If we don't need all that fuel, we can reduce the fuel load to get us down to the MTOW.
But wait! The flight is only two hours long. Using a fuel burn rate of 3200 lbs per hour, we should burn 6,400 lbs. Assuming we are at the MTOW of 143,000 lbs, upon arrival at the destination, the landing weight will be 136,600 lbs. This is 27,600 lbs over the maximum landing weight limit of 109,000 lbs. If we add the predicted fuel burn to the maximum landing weight, we get the true takeoff weight limit. In this example: 109,000 lbs + 6400 lbs = 115,400 lbs MTOW. Subtract the BOW and load, and you get 12,030 pounds. This is how much fuel you can carry, or about 3 hrs and 45 minutes of fuel. With an enroute time of two hours, we should land with 1+45 hrs remaining in fuel. Legal reserves is fuel to destination + fuel to alternate + 45 minutes. So 3+45 works. In this example, we had to reduce the fuel load from 100% to about 25% in order to carry 102 passengers on a two hour flight.
If the flight ideparts at 143,000 lbs (MTOW), it will need to burn just over ten hours of fuel to get down to the maximum landing weight. This is why on shorter flights, maximum landing weight is so important. All the performance charts are based upon remaining within the limitations. Landing overweight means higher landing speeds, which you don't have data for. Landing distances will be longer, brake wear and heat will be greater, structural limits in the landing gear may be exceeded. You have to know your limitations.