Das ist nach Ansicht JEDES CSIP nicht korrekt, vor allem weil Du Gefahr läufst bei der falschen Quele zu landen.

Gelehrt wird, von allen CSIPs,: Am GNS/440/650 umschalten.

Here’s why it’s usually better to switch from GPS1 to VLOC1 on the navigator itself (e.g. IFD or GNS) rather than using the PFD’s CDI softkey:

1. True Source Control vs. Display Control

Navigator (IFD/GNS): When you press the CDI button on the navigator, you are telling the box itself to change its output from GPS → VLOC. The signal that goes to the PFD, MFD, and autopilot changes at the source.
PFD (CDI softkey): On the Entegra PFD, pressing CDI only changes which input the PFD is displaying. The navigator itself may still be outputting GPS. That means the autopilot may be following a different source than what you see on the PFD.

2. Autopilot Integration

The S-TEC or Avidyne DFC autopilot follows the navigator’s selected output.
If you switch only on the PFD, you could be tricked into thinking you’re tracking a VOR/LOC/ILS when in fact the navigator is still sending GPS guidance to the autopilot.
Result: autopilot may happily fly the wrong source, while the PFD makes you believe you’re on the right one → dangerous on an approach.
DFC90: autopilot follows PFD FD commands → but the PFD’s FD still depends on the navigator’s output mode.

3. Procedures & Standardization

IFR checklists and avionics manuals usually instruct: “Switch to VLOC on the navigator”.
That way, what you see, what the navigator outputs, and what the autopilot flies are always aligned.

4. Cross-Side Nav / Redundancy

If you only switch on the PFD, the other side (MFD/second PFD if present, or a second seat display) may show a different picture.

Switching on the navigator keeps all displays and cross-side instruments consistent.