Dear all, thank you for the comments and for your time.
@Sidestick_n_Rudder: Excuse me but I could not understand what you mean with sampling rate of FF?
@FlightDetent:
1) Yes I agree 100%, I didnot expect to see absolutely same FF figures for this long time, but since there are many flights like that, I forced myself to think may be in Airbus, the EEC/ECU could have "extremely" precise command function on fuel control unit.
2) I do not have chance to communicate with the pilots, I just wanted to hear the opinions of pilots here.
3) Then I am absolutely sure that there is something wrong with FDR or data acqusition. I do not think that there might be anything wrong with the engine systems.
@Tinwacker: I am not sure that the problem is caused by the transmitter itself, because (as far as I know) this signal is also used for f.used calculation in DMCs, so if anything happens to the transmitter then a serious fault should be come into view. But the FDRs that I am examining belong to regular flights with no fault. Also, it is interesting to me that the trasmitter function only sticks same value at this specific flight phases, because after on it appears to work normally.
Regards