To determine the allowable landing weight for a transport category airplane, the following details must be considered:
• Airfield pressure altitude
• Temperature
• Headwind component
• Runway length
• Runway gradient or slope
• Runway surface condition
With these details, it is possible to establish the maximum allowable landing weight, which will be the lower of the weights as dictated by:
• Landing runway requirements
• Approach climb requirements
In practice, the approach climb limitations (ability to climb in approach configuration with one engine inoperative) are seldom encountered because the
landing weights upon arrival at the destination airport are usually light. However, as in the second segment climb requirement for takeoff, this approach climb
gradient must be met and landing weights must be restricted if necessary. The most likely conditions that would make the approach climb critical would be the
landings at high weights and high-pressure altitudes and temperatures, which might be encountered if a landing were required shortly after takeoff. Landing field requirements can more frequently limit an airplane’s allowable landing weight than the approach climb limitations. Again, however, unless the runway is particularly short, this is seldom problematical as the average landing weight at the destination
seldom approaches the maximum design landing weight due to fuel burn off.
Manufacturer Requirements
In computing the landing distance required, some manufacturers do not include all of the above items in their charts, since the regulations state that only pressure
altitude, wind, and airplane weight must be considered. Charts are provided for anti-skid on and anti-skid off conditions, but the use of reverse thrust is not used in computing required landing distances.
Regulatory Requirements
The landing distance, as required by the regulations, is that distance needed to land and come to a complete stop from a point 50 feet above the threshold end of the runway. It includes the air distance required to travel from the 50-foot height to touchdown (which can consume 1,000 feet of runway distance), plus the stopping distance, with no margin left over. This is all that is required for 14 CFR part 91 operators (non-air carrier), and all that is shown on some landing distance required charts.
Part 121 Air Carrier Requirements
For air carriers and other commercial operators subjected to 14 CFR part 121, a different set of rules applies which states that the required landing distance
from the 50-foot height cannot exceed 60 percent of the actual runway length available. In all cases, the minimum airspeed allowed at the 50-foot height must
be no less than 1.3 times the airplane’s stalling speed in the landing configuration. This speed is commonly called the airplane’s VREF speed and will vary with
landing weight.
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