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When both failure cases are dealt with separately, the number of critical points and the specific escape routes also increase. As a result, the complexity may engender a supplementary workload for flight crews and a subsequent risk of error. 

This is why, whenever it is possible, it must be preferred to define the same critical points and the same escape routes, whatever the failure case. Thus, the reaction time and the risk of mistake are reduced. In such a case, the route study should be based on the most penalizing descent profile (Figure D16). 

E. LANDING 

1. INTRODUCTION 

To dispatch an aircraft, an operator has to verify landing requirements based on airplane certification (JAR 25 / FAR 25) and on operational constraints defined in JAR-OPS and FAR 121. In normal operations, these limitations are not very constraining and, most of the time authorize dispatch at the maximum structural landing weight. This leads to a minimization of the importance of landing checks during dispatch. However, landing performance can be drastically penalized in case of inoperative items, adverse external conditions, or contaminated runways. Flight preparation is, therefore, of utmost importance, to ensure a safe flight. 

In the next chapters, we will specify landing requirements based on airworthiness rules, and dispatch conditions. A final chapter will address the flight management and the choice of a diversion landing airport. 

2. LANDING DISTANCE AVAILABLE (LDA) 

2.1.  With no Obstacle under Landing Path 

In this case, the Landing Distance Available (LDA) is the runway length (TORA). The stopway cannot be used for landing calculation. 

2.2. With Obstacles under Landing Path 

The landing distance available (LDA) may be shortened, due to the presence of obstacles under the landing path. 

Annex 8 of ICAO recommendations specifies the dimension of the protection surfaces for landing and approach (Approach funnel). 

When there is no obstacle within the approach funnel, as defined below (see Figure E2), it is possible to use the runway length to land. 

However, if there is an obstacle within the approach funnel, a displaced threshold is defined considering a 2% plane tangential to the most penalizing obstacle plus a 60 m margin (Figure E3).

In this case, the Landing Distance Available (LDA) is equal to the length measured from the displaced threshold to the end of the runway. 

3. LANDING PERFORMANCE 

3.1. Operating Landing Speeds 

Originally, the speeds defined in next chapters were manufacturer or operator operating speeds. Today, most of them (as the term VREF the reference landing speed for example) are widely used and understood operationally. The JAR authorities found it convenient to use the same terminology in stating airworthiness requirements and have, indeed, been used in recent requirement amendments. 

3.1.1. Lowest Selectable Speed: VLS 

As a general rule, during flight phases, pilots should not select a speed below VLS (Lowest Selectable Speed), defined as 1.23 VS1g of the actual configuration.

 VLS = 1.23 Vs1g g 

* The 1.23 factor is applicable to the fly-by-wire aircraft (1.3 for the others). 

This rule applies for landing. During landing, pilots have to maintain a stabilized approach, with a calibrated airspeed of no less than VLS down to a height of 50 feet above the destination airport. 

3.1.2. Final Approach Speed: VAPP 

VAPP is the aircraft speed during landing, 50 feet above the runway surface. The flaps/slats are in landing configuration, and the landing gears are extended. 

VAPP is limited by VLS: 

VAPP ≥ VLS 

It is very common to retain a margin on VLS to define VAPP. For Airbus aircraft, in normal operations, the VAPP is defined by:

 VAPP = VLS + wind correction 

Wind correction is limited to a minimum of 51 knots, and a maximum of 15 knots. VAPP is displayed on MCDU APPRoach page. 

The FMGS and managed speed is used to define the VAPP TARGET. It gives efficient speed guidance in approach with windy conditions, since it represents: 

VAPP TARGET = GS mini + actual headwind 

GS mini = VAPP – Tower wind 

Actual headwind is measured by ADIRS, and the tower wind is entered on the MCDU. 

1 When the auto-thrust is used or to compensate for ice accretion on the wings 

3.1.3. Reference Speed: VREF 

In case of failure in flight, emergency or abnormal configuration, performance computations are based on a reference configuration and on a reference speed. VREF means the steady landing approach speed at the 50 feet point for a defined landing configuration. For Airbus, this configuration is CONF FULL.