Originally Posted by
FlightDetent
STBYRUD, that’s plain wrong.
Ondrayy, your captain is perfectly right and you have been undertrained, which is what computerized performance made possible. Not your fault.
The whole of FLEX or Assumed Temperature Thrust is based on iterations using TOGA with ever increasing OAT, until you hit the limit. And then AST = TOGA (OATlim -1). Point here being the entire aerodynamic / accelerating / stopping model is calculated under the
assumed temperatures. Sometimes even higher than the A/C certified limit for the actual operation.
Google for TAT Effect ASDA or similar, your thirst will be satisfied.
. Three direction markers and one warning for you:
- The 3% quoted by EGPFlyer is also found in a UK CAA approved Ops Manual of a very large airline with a deeply knowledgeable performance department. It can be quickly verified if you have access to the full Performace Engineers Package SW.
- F = -a*m
- Ek = 1/2 * m * v * v
- The calculation model of the deceleration phase for RTO does not consider the effect of (wet) paint and rubber deposits towards the far runway end.
Ok, so to sum it up. The Stop Margin calculated by the Take Off Data Computer (LPC-NG).
Is saying that
let's say....
A flex of
60 and the OAT of
20Degrees gives a stop margin of
100m, and that stop margin of
100m will only be achieved
EXACTLY at
100m,
IF THE OAT IS 60 Degrees Celcius??
However,
since the OAT is 20 Degrees the
stop margin number is increased, HENCE reduces the ASD.
Lets say the takeoff is rejected at V1 exactly (or a few knots just before V1), the
actual stop margin is lesser than that of "
100m" SINCE THE ACTUAL OAT is 20 degrees not 60 Degrees.
Thanks for the new formula, so here is my calculation based on what you guys just explained...
Calculated ASD with a flex of
60 by the LPC-NG on a runway length of
2000m gives
1900m (since the stop margin is
100m)
Actual OAT is
20 Degrees
ASD is reduced by
3% x (
60-
20)/
10 =
12% of 1900m =
228m
Actual ASD is
1900 -
228 =
1672m ASD with the OAT of
20 degrees and flex of
60
Therefore the New Stop Margin with actual
OAT of 20 and flex of 60 is 100m + 228m = 328m
I hope I'm right about this as it takes quite sometimes to get my head right about this complicated topic
