A320 LPC quiz

[Flyman35]

Sometimes when the aircraft is not heavy I see a significant low V1 speeds on the LPC like 110 knotes, however in the RTOW the minimum V1 is 113 , my question: does the LPC take minimum V1 into consideration or we shall use the minimum V1 in the RTOW, thanks.:yuk:

[rbhojwani]

The LPC does take into account minimum V1 (as a function of Vmc) and many other little parameters. The discrepancy may have taken place because there are significant systematic errors in RTOW charts, whereas LPC is assumed to be a more precise calculation. Go with LPC.

[FlightDetent]

Agree with the above. The RTOW usually have the margins applied in a conservative way, so you are not getting as close to the applicble limiting value, as you might with LPC.

The core limiting figures are indeed the same for any method of calculation.

Well spotted about the 110 being a low value worth attention. For the CFM version, at sea level ISA, the VMCG is 111/109 kts. See FCOM-LIM-AG-SPD Minimum control speeds

[Flyman35]

rbhojwani,FlightDetent,
Thanks for your contribution and clarification.

[john_tullamarine]

there are significant systematic errors in RTOW charts

Ought not to be any significant errors at all .. certainly one applies some conservatism while running up the RTOW data but it is only a very minor consideration.

The only situation I could see where a problem might arise is if someone ran up a quick and dirty RTOW data set .. but, in that case, why not let the crews use the usual general takeoff data protocols as there would only be justification to incorporate the errors to get you out of a jam on the odd occasion ?

Might one enquire whence come your significant systematic errors ?

[vilas]

LPC is correct. However there are no significant errors in RTOW charts but a situation where it is possible to get V1 lower than that is shown at the bottom of the chart as minimum V1.
According to Airbus

The Minimum V1 at the bottom of the chart is calculated by adding
The maximum VMCG on complete chart
+
The maximum (V1-VEF) (complete chart)

For a given point, V1 can be less than this minimum value if (VEF=VMCG) and (V1-VEF) is less than (MAX V1-VEF)