The method is far less elaborate, based on the (only available) TOGA certification data. You could do AST Method with Tu-134 if you had the N1 tables.
A very helpful Boeing presentation attached.
The additional
margin when
ASDA-ASD difference shows 0 grows from the two main discrepancies
- V1 expressed in IAS is reached geometrically earlier due to TAS (= GS assuming zero wind) being lower
- The kinetic energy at the start of braking is
significantly less in reality compared to the mathematical model used to calculate the perf due to the V squared.
That's it. Mass is the same and Thrust is made equal by setting the reduced N1/EPR.
For a typical 65 t, on a 2700 m RWY with 45 FLEX in 15°C air
- you have only 85ish% of energy to kill
- deceleration begins about 80 meters sooner.
compared to the calculated.
The full autopsy would show another (small) benefit from the difference in air density, which is squarely
beyond my ken.