john_tullamarine, well as earlier agreed TOW isn・t RWY limited, but was climb limited. The actual funnel starts at the actual TOD, which might be way before the end of TODA for the given weight and prevailing conditions, if the TODA is significantly higher then required. Therefore shifting the actual TOD over the TODA, which is TORA+CLEAR WAY, will lead to increased V1/Vr & V2/Vs ratio resulting in:
An increase in MTOW limited by
the:
First segment
Second segment
Obstacles
Not influencing the MTOW limited
by the:
Final takeoff segment
Maximum Takeoff Weight
For a given V2/VS ratio, it is possible to find
an optimum MTOW and its associated optimum V1/VR ratio.
For each V2/VS ratio comprised between V2/Vsmin and V2/Vsmax, such a
determination is carried out. In the end, the highest of all the optimum MTOWs and
associated optimum V1/VR is retained. It therefore corresponds to an optimum V2/VS
ratio. The result of the optimization process is, for a given runway and given takeoff
conditions:
Result of the optimization process
The highest possible MTOW
The optimum V1/VR ratio
The optimum V2/VS ratio
The same result could be achieved using the derated thrust method if the TAKE OFF would be RWY limited:
A reduction in the minimum control speeds sometimes generates a takeoff
performance benefit (higher MTOW) when taking-off on a short runway. Indeed, the
decision speed V1 is the maximum speed at which it is still possible to reject the
takeoff and stop the aircraft within the runway limits. Nevertheless, V1 must be
greater than VMCG, and the Accelerate Stop Distance is often the most constraining
limitation on a short runway. A reduction of the VMCG can then permit a reduction of
the ASD for a given takeoff weight, and lead to better takeoff performance when the
MTOW without derate is ASD/VMCG limited.
Ignition Override,
To answer your question you need to refer to FAR. Dependable on art of operation under FAA dispatcher and commander bear the joint responsibility for the safe conduct of the flight. It・s not the case under JAR. Under JAA the dispatcher doesn・t bear the responsibility for the flight safety, he only provides necessary information. In fact many companies don・t even have a dispatch department, but performance engineering dep.
I recall a flight from CUN to MSP where we had to divert to Loredo in Texas and that one was uncontrolled airport by night with visual approach and departure, but calculated performance. It wasn・t a scheduled flight, but it happened quite often due to customs operating hours. So as you can see you might fly to the airdromes without IFR charts and then it・s your responsibilities as a commander to ensure obstacle clearance.
Cheers.
