(Ed. Note: The following is taken from a folio of safety training for commercial pilots, but which also serves as a useful reminder to GA pilots of the need to know everything current about your destination before you leave the ground)
ICAO defines the term 'Landing Distance' as "the horizontal distance traversed by the aeroplane by the aeroplane from a point on the approach path at a selected height above the landing surface to the point on the landing surface at which the aeroplane comes to a complete stop". This is usually taken as the basis for the determination of the Landing Distance Required (LDR)which is calculated by accounting for the effect of various influencing factors, including prevailing surface conditions and the extent to which aircraft devices which are available to assist deceleration are deployed,
A definition of the Landing Distance Available (LDA)is "the length of the runway which is declared available by the appropriate Authority and is suitable for the ground run of an aeroplane landing".
Obviously, the LDR must be less than the LDA!
Calculation of LDR
The LDR depends on a number of factors, principally:
· The aircraft landing mass
· The surface wind and temperature
· The runway elevation and slope
· The runway surface conditions (dry, wet or contaminated)
· The condition of aircraft braking systems
Aircraft performance (LDR and landing speed) is calculated by the pilot taking account of the above factors, and including the SAFETY FACTOR.
It is assumed for these calculations that the aircraft will be at a specified height (normally 50 ft) crossing the runway threshold at the correct speed, and that aircraft handling will be in accordance with procedures detailed in the POH.
These vary according to the aircraft type, the runway conditions (dry, wet or contaminated) and pre-departure planning as to whether the airfield is the destination or an alternate. Special provisions will apply to steep approaches and to short landing operations.
Factors Affecting Actual Landing Distance
Landing an aircraft is a process during which the pilot must achieve the following goals:
· On passing the runway threshold:
o 50 ft above runway threshold
o Aircraft configured for landing (landing gear, flaps and slats, etc.)
o Correct and steady forward speed
o Correct and steady descent rate
o Appropriate power setting
o Wings level
· On touch-down:
o Brakes applied
o Power reduced
o Directional control maintained
Unserviceability of any devices which affect the aircraft braking (brakes, anti-skid, etc.) can have a serious effect on landing performance. Major unserviceability (e.g. engine malfunction) complicates handling considerably; but any unserviceability, even if not serious on its own, may add to control difficulties.
The complexity of the task is such that even in ideal conditions, a perfect landing is virtually impossible, while any deviation from the ideal adds to the actual landing distance.
The maximum landing mass and the landing speed depend on the runway braking conditions. If these have been inaccurately reported or if the runway is wet or contaminated when its condition was reported as being dry, the landing distance achieved will be increased.
The presence of standing water, snow, slush or ice on the runway has a particularly serious effect on landing performance and if it cannot be cleared, it must be reported as accurately as possible. Special techniques must be used by pilots when landing on contaminated runways.
The maximum landing mass and landing speed is calculated based on the reported wind and temperature. Significant changes to the reported conditions will affect the landing distance achieved.
Strong cross-winds, turbulence and wind shear make handling difficult and are likely to result in an increased landing distance.
Effect of Factors on Landing Distance Required
Flight Safety Foundation (FSF) “Approach-and-landing Accident Reduction (ALAR) Briefing Note 8.3 — Landing Distances” includes the following approximate effects of various factors on landing distance:
· Airfield elevation: add 5-10% to LDR per 1000ft. elevation, depending on runway conditions
· Runway slope: add 1% to LDR per 1% downhill slope
· Runway conditions: Wet add 30-40% to LDR; Standing Water/Slush add 100-130% to LDR; Compacted Snow add 60-70% to LDR; Ice add 250-350% to LDR
· Wind: add 10% to LDR per 10 kt. headwind; add 30% to LDR per 10 kt. tailwind
· Threshold airspeed: add 20% to LDR per 10% speed increase above target airspeed
· Threshold height: add 1000 ft. LDR for each 50 ft above recommended target (50 ft)