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The terms Landing Distance Required (LDR) and Landing Distance Available (LDA) routinely defined in aircraft landing performance documentation are not defined for fixed wing aeroplanes in International Civil Aviation Organisation (ICAO) SARPs.
ICAO SARPs define 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" (ICAO Annex 8 Part IIIA Paragraph 126.96.36.199. and Part IIIB Sub-part B Paragraph B2.7 e)). This is usually taken as the basis for the determination of Landing Distance Required (LDR) which is calculated by taking into account 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 provided in IR-OPS Annex I - Definitions, as "the length of the runway which is declared available by the appropriate Authority and is suitable for the ground run of an aeroplane landing".
Calculation of LDR
Put simply, the LDR must be less than the LDA.
IR-OPS CAT.POL.A (and EU-OPS 1 Sub-part G) specifies safety factors that must be applied in determination of the LDR (see further reading).
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); and,
- The condition of aircraft braking systems.
Aircraft performance (LDR and landing speed) is calculated by the pilots using printed tables or a computer. This calculation takes account of the above factors, 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 Aircraft Flight Manual (AFM) and company Standard Operating Procedures (SOPs).
Safety factors vary according to the aircraft type (turbo-jet or turbo-prop), the runway conditions (dry, wet or contaminated) and in pre-departure planning, whether the airfield is the destination or an alternate.
Special provisions apply to steep approaches and to short landing operations.
Factors Affecting Actual Landing Distance
Landing an aircraft is a difficult process requiring considerable manual dexterity. The pilot must achieve the following goals:
- On passing the runway threshold:
- 50 ft above runway threshold;
- Aircraft configured for landing (landing gear, flaps and slats, etc.);
- Correct and steady forward speed;
- Correct and steady descent rate;
- Appropriate power setting;
- Wings level.
- On touch-down:
Unserviceability of any of the devices which affect the aircraft braking (brakes, anti-skid, reverse thrust, lift-dump, etc.) can have a serious effect on landing performance. (Note: landing performance calculations normally assume that reverse thrust is not available)
Major unserviceability (e.g. engine malfunction) complicates handling considerably; however, any unserviceability, even if not serious on its own, may add to control difficulties.
The complexity of the task (even with Autoland) 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.
Effect of Factors on Landing Distance
Flight Safety Foundation (FSF) Approach-and-landing Accident Reduction (ALAR) Briefing Note 8.3 — Landing Distances contains the following diagram which shows the approximate effects of various factors on landing distance:
- Figure 2 - Landing Distance Factors
Related ICAO Provisions
- ICAO Annex 8: Airworthiness Part III Chapter 2
- For CAT A aircraft see: IR-OPS CAT.POL.A.230 & 235
- For CAT B aircraft see: IR-OPS CAT.POL.A.330 & 335
- For CAT C aircraft see: IR-OPS CAT.POL.A.435
- See also Acceptable Means of Compliance and Guidance Material to the parts of IR-OPS CAT.POL.A listed above
- EU-OPS 1: Sub-part G, especially EU-OPS 1.510, EU-OPS 1.515 and EU-OPS 1.520 and associated AMCs and appendices relate to Performance Class A operations. Sub-parts H and I contain provisions relating to Performance Group B and C aircraft respectively.
Flight Safety Foundation
The Flight Safety Foundation ALAR Toolkit provides useful training information and guides to best practice. Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR website.