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Air Carrier Obstacle Clearance Requirements (Part Two) Landing Performance

by Flight Learnings

in Aircraft Performance

As in the takeoff planning, certain speeds must be considered during landing. These speeds are shown below.

  • VSO—stalling speed or the minimum steady flight speed in the landing configuration.
  • VREF—1.3 times the stalling speed in the landing configuration. This is the required speed at the 50-foot height above the threshold end of the runway.
  • Approach climb—the speed which gives the best climb performance in the approach confguration, with one engine inoperative, and with maximum takeoff power on the operating engine(s). The required gradient of climb in this configuration is 2.1 percent for two-engine aircraft, 2.4 percent for three-emgine aircraft, and 2.7 percent for four-engine aircraft.
  • Landing climb—the speed giving the best performance in the full landing configuration with maximum takeoff power on all engines. The gradient of climb required in this configuration is 3.2 percent.

Planning the Landing

As in the takeoff, the landing speeds shown above should be precomputed and visible to both pilots prior to the landing. The VREF speed, or threshold speed, is used as a reference speed throughout the traffic pattern or instrument approach as in the following example:

VREF plus 30K Downwind or procedure turn

VREF plus 20K Base leg or final course inbound to final fix

VREF plus 10K Final or final course inbound from fix (ILS final)

VREF Speed at the 50 foot height above the threshold

Landing Requirements

The maximum landing weight of an aircraft can be restricted by either the approach climb requirements or by the landing runway available.

Approach Climb Requirements

The approach climb is usually more limiting (or more difficult to meet) than the landing climb, primarily because it is based upon the ability to execute a missed approach with one engine inoperative. The required climb gradient can be affected by pressure altitude and temperature and, as in the second segment climb in the takeoff, aircraft weight must be limited as needed in order to comply with this climb requirement.

Landing Runway Required

The runway distance needed for landing can be affected by the following:

  • Pressure altitude
  • Temperature
  • Headwind component
  • Runway gradient or slope
  • Aircraft weight

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 aircraft 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.

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.

For air carriers and other commercial operators subject to 14 CFR part 121, a different set of rules applies stating 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 aircraft’s stalling speed in the landing configuration. This speed is commonly called the aircraft’s VREF speed and varies with landing weight. Figure 10-38 is a diagram of these landing runway requirements.

Figure 10-38. Landing runway requirements.

-Click to Enlarge- Figure 10-38. Landing runway requirements.

1 Nabil Kutbi Alsaiyed June 12, 2011 at 3:28 am

You are great, really helpful

Mgr, Aerodrome Standards and Safety
General Authority of Civil Aviation
Saudi Arabia

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