Answer fm Airboos on this very topic:
"It seems that in the past the FCOM used to state that takeoff shift entry was not required on the PERF TAKEOFF page if the GPS is available. This statement was applicable to FMS 2: When the GPS PRIMARY is available, the aircraft position update is performed as soon as the takeoff thrust is applied taking into account the GPS position. Due to the accuracy of the GPS position, even, if the takeoff is not performed from the runway threshold, the takeoff shift that may have been entered in the PERF TAKEOFF MCDU page is, as a consequence, not taken into account.
The FCOM statement you refer too is no longer in the FCOM for the following reasons:
- Commonality between GPS and non-GPS equipped aircraft as per SOP;
- To cover the possible non availability of the GPS and therefore, to ensure that the crew will not risk forgetting the TO SHIFT.
Hoping the above clarifies, please feel free to contact this office again, if you have any questions.
Best regards.
Nicolas VITU-BARBIER
A320/A330/A340 Operational Standards"
No need if GPS Primary then.
Regards,
mcdhu