Originally Posted by
EmDeer
In our outfit most of the crews do one of two things when the stopmargin is only a few meters: either use "runway shortening from the beginning", or raise your take-off mass by 500kg.
This shows a general lack of understanding of aircraft performance and Airbus FlySmart calculations. You should ask your Tech Pilot for a briefing to correct this. You are achieving absolutely nothing by those small adjustments.
Maximum engine wear saving is achieved by the first few degrees of Flex. That benefit is lost with ‘creative accounting’.
The accelerate-stop distance on a dry runway is the greater of the following values:
a) ASDN-1 dry = Sum of the distances necessary to:
- Accelerate the airplane with all engines operating to VEF
,- Accelerate from VEF to V1 (1) assuming the critical engine fails at VEF and the pilot takes the first action to reject the takeoff at V1
- Come to a full stop (2,3)
- Plus a distance equivalent to 2 seconds at constant V1 speed
1 Delay between VEF and V1 = 1 second
2 ASD must be established with the “wheel brakes at the fully worn limit of their allowable wear range” [JAR/FAR 25.101]
3 ASD shall not be determined with reverse thrust on a dry runway
b) ASDN dry = Sum of the distances necessary to:
- Accelerate the airplane with all engines operating to V1
, assuming the pilot takes the first action to reject the takeoff at V1
- With all engines still operating come to a full stop
- Plus a distance equivalent to 2 seconds at constant V1 speed
ASDdry = max of {ASDN-1 dry, ASDN dry}
The accelerate-stop distance on a wet runway is the greater of the following values:
• ASDdry • ASDN-1 wet = same definition as ASDN-1 dry except the runway is wet1
• ASDN wet = same definition as ASDN dry except the runway is wet
ASDwet = max of {ASDdry, ASDN-1 wet, ASDN wet}
Influence of V1 on Accelerate-Go/Stop Distances
For a given takeoff weight, any increase in V1 leads to a reduction in both TODN-1 and TORN-1. The reason is that the all engine acceleration phase is longer with a higher V1 speed, and, consequently, in case of an engine failure occurring at VEF, the same V2 speed can be achieved at 35 feet at a shorter distance.
On the other hand, TODN and TORN are independent of V1 as there is no engine failure, and thus no consequence on the acceleration phase and the necessary distance to reach 35 feet.
On the contrary, for a given takeoff weight, any increase in V1 leads to an increase in both the ASDN-1 and ASDN. Indeed, with a higher V1 speed, the acceleration segment from brake release to V1 is longer, the deceleration segment from V1 to the complete stop is longer,
and the 2 second segment at constant V1 speed is longer.