The landing distance LD being a direct function of the energy E, the corresponding increase in landing distance ( DLD ) can be expressed also as:
DLD ( in % ) = 2 x D VAPP ( in % )

Note :
The above rule assumes a normal flare and touchdown (i.e., not allowing the aircraft to float to bleed off the excess speed).
Height over threshold:
Crossing the runway threshold at 100 ft results in an increase of the landing distance of typically 1000 ft or 300 m, regardless of the runway condition and aircraft model.

Figure 3

Factors Affecting Landing Distance
Page 3

AIRBUS INDUSTRIE Getting to Grips with
 Flight Operations Support Approach-and-Landing Accidents Reduction

Flare technique:
Performing a long flare (i.e., allowing the aircraft to float to bleed off an excessive speed) further increases the landing distance.
For example, a 5 % increase (excess) of the final approach speed increases the landing distance by:

Performing a power-on touchdown in an attempt to lessen an excessive rate-of-descent or to smooth out the touchdown results in:
.  
A long flare; and,

.  
The inhibition of the automatic extension of ground-spoilers.

This increases the risk of bouncing upon touchdown and of a subsequent hard landing.
Ground spoiler not armed:
Failure to arm the ground spoilers (usually in conjunction with thrust reversers being inoperative) is frequently a causal factor in runway overruns.
The ground spoilers extend automatically when reverse thrust is selected (regardless of whether the ground spoilers are armed or not); this design feature must not be relied upon for extension of ground spoilers. Ground spoilers must be armed per SOPs.
Failure to arm the ground spoilers results in a typical landing distance factor of 1.3 (1.4 if thrust reversers are inoperative).
The automatic extension of ground spoilers should be monitored and announced by calling Ground Spoilers or No Spoilers.
Note:
On A300/A310 series, if ground spoilers do not
deploy automatically, the PF can manually extend the
ground spoilers using the speed brakes lever.

Delaying the derotation (i.e., the nose landing gear touchdown) maintains a higher lift on main landing gears for longer, resulting in less load on the main landing gears and, hence, in less braking efficiency.
This also delays the spin-up signal from the nose-wheels; this signal is required for the optimum operation of the anti-skid system.
MEL conditions:
When operating under the provision of the MEL for an item affecting the landing speed, the lift-dumping or the braking capability, the applicable landing speed correction and landing distance factor must be accounted for.
Systems malfunctions:
System malfunctions, such as an hydraulic system low pressure, may result in multiple effects on the landing speed and landing distance, such as:
.  
Landing speed correction due to slats or flaps inoperative (i.e., restoring the stall margin);

.  
Landing speed correction due to loss of roll spoilers (i.e., restoring the maneuverability);

.  
Landing distance factor due to loss of ground spoilers (i.e., loss of lift dumping capability); and,

.  
Landing distance factor due to loss of normal braking system (i.e., reduced braking capability).

The FCOM and QRH provide the applicable final approach speed corrections and landing distance factors for all malfunctions (including their consequential effects).
Factors Affecting Landing Distance
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AIRBUS INDUSTRIE
 Flight Operations Support

Combining Landing Distance Factors
The landing distance factors provided in the FCOM and QRH take into account all the consequential effects associated with the primary malfunction.
　
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