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That gives:

 VREF= VLS in CONF FULL 

In case of a system failure affecting landing performance, Airbus operational documentation indicates the correction to be applied to VREF to take into account the failure: 

VAPP = VREF + VINOP 

Another speed increment can be added to VAPP to account for wind, when needed. 

3.2. Actual Landing Distance (ALD) 

3.2.1. Manual Landing 

“JAR/FAR 25.125 

(a)The horizontal distance necessary to land and to come to a complete stop from a point 50 ft above the landing surface must be determined (for standard temperatures, at each weight, altitude and wind within the operational limits established by the applicant for the aeroplane) as follows: 

The aeroplane must be in the landing configuration 

A stabilized approach, with a calibrated airspeed of VLS must be maintained down to the 50 ft.” 

During airplane certification, the actual landing distance is demonstrated as follows: 

It is the distance measured between a point 50 feet above the runwaythreshold, and the point where the aircraft comes to a complete stop. 

To determine this actual landing distance, several conditions must be achieved: 

Standard temperature 

Landing configuration 

Stabilized approach at VLS (or VMCL whichever is greater) for the configuration for manual landing. 

Non excessive vertical acceleration 

Determination on a level, smooth, dry, hard-surfaced runway 

Acceptable pressures on the wheel braking systems 

Braking Means other than wheel brakes: Spoilers, reversers (except on dry runway), can be used when they are safe and reliable. 

Actual landing distance is also certified with degraded braking means (spoiler inoperative, one brake inoperative…). 

Actual Landing Distances are certified on dry runways for all Airbus aircraft, certified on contaminated and icy runways for all fly-by-wire aircraft and published (for information) for wet. 

Demonstrated landing distances will not account for reversers on dry runways. The reverse thrust influence may be considered on contaminated runways. 

On dry runways, landing distances are demonstrated with standard temperatures, according to JAR/FAR 25. However, on contaminated runways, Airbus decided to take into account the influence of temperature on landing distance demonstration. This choice ensures added safety as it gives a conservative ALD. 

Landing distance data must include correction factors for no more than 50% of the nominal wind components along the landing path opposite to the landing direction, and no less than 150% of the nominal wind components along the landing path in the landing direction. This is already taken into account in published figures and corrections. 

3.2.2. Automatic Landing 

The required landing distance must be established and scheduled in the airplane Flight Manual, if it exceeds the scheduled manual landing distance. 

On a dry runway, the ALD in autoland is defined as follows:

  ALD = (Da + Dg) 

Where : Da is the airborne phase distance Dg is the ground phase distance. 

The airborne phase Da is the distance from the runway threshold up to the glideslope origin (d1), plus the distance from the glideslope origin up to the mean touchdown point (d2), plus three times the standard deviation of d2 (σd2). 

The distance from the glideslope origin to the mean touchdown point (d2), as well as its corresponding standard deviation (σd2), have been statistically established from the results of more than one thousand simulated automatic landings. 

The Ground Phase Dg for an automatic landing is established as with a manual landing, assuming a touchdown speed equal to the mean touchdown speed (VTD) plus three times the standard deviation of this speed (σVTD). 

3.3. Go-Around Performance Requirements 

A minimum climb gradient must be observed, in case of a go-around. The minimum air climb gradients depend on the aircraft type. 

3.3.1. Approach Climb 

This corresponds to an aircraft’s climb capability, assuming that one engine is inoperative. The “approach climb” wording comes from the fact that go-around performance is based on approach configuration, rather than landing configuration. For Airbus fly-by-wire aircraft, the available approach configurations are CONF 2 and 

3. 

3.3.1.1. Aircraft Configuration 

One engine inoperative 

TOGA thrust 

Gear retracted 

Slats and flaps in approach configuration  (CONF 2 or 3 in most cases)