FMS question

[se1776]

How is the FMS classified? Celestial or ground navigation.

Can you shoot a VOR or NDB approach by only using the FMS and not the NAV Radios?

Where can I get more info?

I understand you always need to tune and ID your radios, but how about if any of your NAV radios are INOP.

 

[Bringupthebird]

It depends.

Primarily it's ground-based, but some have a GPS input. It uses a combination lat-long and DME's to fix a constantly updated position. Flight tracks (enroute and approach) are developed over lat-long based waypoints and compared to the aircraft's constantly updated position.

Non-precision approaches (referred to as managed non-precision approaches) are generally flight tracks that overlay the published approach course. Raw data is monitored by the pilots and requires nav ID and raw data to be displayed at least on one side. The FMS builds a vertical path from the FAF and allows a constant descent in most cases to the MAP (or VDP). Prior to shooting the approach, you must verify that the nav accuracy or Required Navigational Performance (how close the airplane is to where it thinks it is) is within specified limits.

Non-managed non-precision approaches are flown in heading mode to stay on the required radial or bearing and some of them have a flight path angle that approximates the required decent path from the FAF to the MAP or VDP.

RNAVand GPS approaches do not require this raw data monitoring and are rapidly replacing most non-precision approaches.

 

[FL510in10min]

I know the CRJ has a GPS bias built in.

 

[se1776]

thanks guys

 

[Bringupthebird]

Oh, and the Airbus autopilot can only fly over an FMS path or Localizer. It doesn't have a NAV input from VORs to the autopilot, like other airplanes.

 

[flatspin7]

The 737 FMC takes information from the IRUs (Inertials), VOR/DME, and GPS (if equipped) to compute position, its all transparent. On the classics you just have to make sure the radio is in auto. The NGs automatically do their thing regardless of what you have tuned in... you fly around with 108.0 in it until you need the radio to shoot am approach or secondary nav. The GPS is usually the most accurate, but our -300s dont have it but they manage. sorta

 

[HA25]

Oh, and the Airbus autopilot can only fly over an FMS path or Localizer. It doesn't have a NAV input from VORs to the autopilot, like other airplanes.

You sure? I think it's GPS primary, with ADIRU (IRU part) next, then DME/DME, the VOR/DME that generates the track.. The MD11 was same.

EDIT: nevermind, I re-read your post again and I agree... there is no "VOR" NAV mode..

 

[flatspin7]

Whilst I have not flown it.. I think the 757 has a similar deal where it cannot track a raw VOR radial, you need to use the FMS or Heading Select.

 

[DrewBlows]

The AIM has extensive information on GPS.

 

[ultrarunner]

How is the FMS classified? Celestial or ground navigation.

Can you shoot a VOR or NDB approach by only using the FMS and not the NAV Radios?

Where can I get more info?

I understand you always need to tune and ID your radios, but how about if any of your NAV radios are INOP.

SE1776, it all depends upon the airplane and the specific installation.

Most corporate aircraft FMS's have GPS sensor inputs and use a combination of GPS VOR VOR/DME. Installations such as this will typically have you keep the CDI in the GPS mode. The autopilots of these planes will couple to the GPS needle or the VOR needle.

On the airline side of things, it can be a bit different, and even different among same-type planes within an airline.

Quite a few airlines have IRU's in which you tell FMS where it is before departing (gate coordinates, runway end coordinates, etc), and the FMS keeps track of things as you move through the sky.

Some airlines installed FMS's that were only VOR/VOR DME and had no GPS function at all. In the latter, you do like we all did...tune and ID pretty much.

It just depends.