Proline 21 - "GNSS REVERTED" error
 

Hello

RE: B-350 dual FMS, Proline-21 install.

We normally sync both units to Number-1 (left side). On todays flight we had GNSS REVERTED error message and it was determined by going to GNSS1 POS page that GNSS1 was in GPS MODE ACQUISITION and only seeing 1 satellite. GNSS2 POS was in GPS MODE NAV and seeing 10 satellites. We then de-synced both FMS units and used FMS-2 as primary (we did not sync the left to the #2/right side in concern for some sort of cross contamination or weird issues) and left FMS-1 as merely a radio tuning device. FMS-2 was used for everything during the flight.

We also have a yellow "TERR" (terrain failure/not working) indicator on the Pilot Displays.

Any ideas on how to resolve this or what did I miss ? We are flying it again tomorrow and will continue to play with it. Back "at base" with avionics and MX support at end of week. Phone calls have gone out but I wanted to ask the forums as a resource for information.

Thank You....

Well, the TERR annunciation is easy--no GPS input for pilot's side. The REVERTED message means #1 is working off its reversion GPS, that is, #2.

First, start up in the morning and all might be well. Watch POS SENSORS page during INIT process and see if it goes to NAV. Might be a bad GPS in the left FMS. I wouldn't think sync'ing them both using # 2 as master is a problem, but going with one FMS wouldn't be either, if MEL allows it.

GF

PS not a BE350 guy, but lots of PL21 time.

Yes roger that on REVERTED and TERR, I guess my bigger question is what is causing this and if anything on-the-road-pilot-wise can be done.

thank you Galaxy, I will check it out tomorrow. Thanks again

Did this occur during pre-flight or after being airborne? It's not covered anywhere, but the GPS unit needs to have the almanac downloaded during INIT, I don't think you can see it happen, if the FMS can't acquire satellites that might be the cause. The almanac tells the receiver the ephemeris info about the satellites--orbits, times, etc. It should download, but takes awhile--minutes.

Was #1 FMS worked on or completely powered down with the internal battery removed? I think the FMS has an internal battery that holds the VM alive--it might be dead.

Probably not, if it doesn't power up OK tomorrow.

GF

middle of cruise flight. I will see how it behaves on today's flight.

How'd it work out?

GF

Magically it worked fine.......I will keep an eye on it, thanks Galaxy !

Good to hear. Try to talk with your maintainers on the FMS battery. I can't say for sure on PL21, but the Honeywell system does have one and it can be a problem.

GF

Sure will, thanks again