A320 SEC PERF unavailable

[Check Airman]

HI all,
As part of my arrival preparation, I'll enter a different runway on the secondary flightplan. At some point, the PERF prompt at R2 on the SEC FPLN page disappears, and I can't change any of the data without copying the active fpln, or rebuilding the secondary.

Why does it disappear?
When exactly does it disappear?
How do I change the data on the SEC PERF pages with the prompt missing?

[Goldenrivett]

When exactly does it disappear?
As soon as the "from - to" positions differ between the active and secondary flight plans.

Why does it disappear?
I didn't write the cr@p software so don't know.

How do I change the data on the SEC PERF pages with the prompt missing?
You have to change the performance data in the secondary whilst both flight plans have the same "from to" way points common in their flight plans, or do it after you've activated the secondary flight plan.

[FlightDetent]

As explained, perform any DCT-to on the primary and the prompt is gone. Not sure what is the effect of simply overflying the next WPT, the behaviour might be different among various FMC setups.

[pineteam]

You can recover it by sequencing the secondary flight plan.

[AB335]

You should be able to activate the secondary in heading mode

[Check Airman]

Thanks guys. I think goldenrivet may have hit on it. I'll keep an eye out next time I go fly.

[Check Airman]

goldenrivet was absolutely right. Checked it today.

[MD83FO]

ive also seen how some secondary flight plans loose predictions when on descent mode.