FMS Using while NPA

[Andrew_Flora]

Again...

So, is it legally to execute the Non-precision (for example, VOR) approach using RNAV equipment (FMS) without monitoring of raw NAVAID (VOR) signal, specifically lateral deviation from NAVAID reference CRS.

Or, what should I do if FMS commands to steer right, but VOR raw data - to steer left ?

[bucket_and_spade]

We have to monitor raw data but can let LNAV (Boeing) fly it and various vertical modes can be used. The raw data takes precedence (assuming it's sensible) so if there was a large difference we'd be expected to switch to the heading select mode to get back on the radial/QDM etc.

Pure GNSS approaches have no raw data to monitor, just ANP versus RNP so we obviously fly these exclusively through the FMC.

[733driver]

Company SOPs may dictate what you have to do but as a rule if it is not a stand-alone R-NAV (GPS etc) approach then you have to display and monitor the nav-aid. If there is a signifigant difference between the nav-aid and the FMS/FMC track then you must follow the nav-aid (VOR, NDB) or go arround. You must go around if the nav aid shows a more than 5 degree deviation from the published inbound course.

You can fly VOR and NDB approaches in L-Nav and V-Nac (or V/S) but you must monitor raw data and vertical profile. My company does that but flies LOC approaches in LOC/VS

[Phil Squares]

I will argue, it depends.

If you have a FMS with GPS updating monitoring the raw data is not really necessary. The updating will make the actual track flown much more accurate than the VOR could ever hope to be.

Granted back before GPS updating when we had just DME/DME, VOR/VOR etc., you did have a requirement to verify the raw data.

How accurate will a NDB approach be with TRWs in the area?????

[733driver]

more accurate yes, legal no, I think.

[Denti]

In the outfit i'm flying for it is recommended to monitor raw data, but not required anymore. However once the ANP exceeds the RNP coded for the approach in the database we have to go around. Only exception is a LOC approach where we still use raw data as the main lateral input. All non precision approaches are flown exactly the same as ILS approaches using the same autoflight modes and indications (737). The presentation is of course a virtual flight path computed by the FMC, so even flying "raw data" or better named flight director off without autopilot it is still flying not according to true raw data (except the LOC needle).

[733driver]

Hi Denti

That is interesting. I wonder how that works legally. What's the point in publishing an approach based on a navaid and then being allowed to disregard that nav aid?

I suppose in your outfit it's the same for SIDss and STARS then? No need to tune anything?

Is it really legal to treat everything as if it was a stand-allone RNAV procedure?

I admit not being up to speed with the legal stuff (with the exception of my company's part A, B etc) but it seems strange to me

[RAT 5]

If you have a FMS with GPS updating monitoring the raw data is not really necessary. The updating will make the actual track flown much more accurate than the VOR could ever hope to be.

Are you allowed to fly an FMS/GPS approach if the required nav aid(s) are u/s? I don't think so. Thus if the nav aids have to b serviceable then common sense says they should be monitored, SOP's or not.

[Denti]

Indeed, we do not tune anything for SIDs or STARs. Some of us more old fashioned ones still do for SIDs, but it is not required at all. For STARs we don't set anything, if anything is set at that point it is approach related.

To be honest, a NAV setup for example for those zurich departes is pretty much impossible anyway as there are so many frequency changes that two navs with two frequencies each are not sufficient, especially considering the OEI SIDs which are of course different.

[Rick777]

The last place I flew required you to monitor raw data if available, but we had some planes (A320) with no ADF installed and could still fly NDB approaches. I think a lot depends on your company's ops specs.

[Check Airman]

more accurate yes, legal no, I think.

That's the heart of the matter. I don't think many people would argue that the GPS signal is superior to a VOR signal, but it's more of a legal matter.

At my company, the PF will fly using FMS data, and the PM will monitor raw data.

[Phil Squares]

Are you allowed to fly an FMS/GPS approach if the required nav aid(s) are u/s? I don't think so. Thus if the nav aids have to b serviceable then common sense says they should be monitored, SOP's or not.

To be honest, yes! Our aircraft have no NDBs installed but we are allowed to fly NDB approaches. As long as the ANP is at or better than the RNP we have no requirement to monitor the nav aids. In this and the last two companies it's been like that going back to early 2000.

As has been pointed out, do you "hard tune" nav aids on departure? If so, I can point out where the FCOM (both A and B) recommend otherwise.

[Andrew_Flora]

I see the next main points:

1) It's recomended to monitor raw data of reference NAVAID regardless of pilot technique;
2) I can USE the FMS if it's certified for RNAV APCH with RNP 0.3 with controlling of ANP not more than RNP. Otherwise:
3) I MUST fly using only raw data - with autopilot or FD in NOT LNAV mode, or with manual control;
4) If I see the difference between FMS and NAVAID lateral deviation, I must maintain the zero-deviation of NAVAID raw signal, not a FMS. The reason for that - the posiibilities of mistakes in FMS nav data base.

[RAT 5]

Phil Squares: under which authority do you operate? Under the EU ones which I've been subjected to a solo BRNAV approach is not allowed. It is an FMC approach flown in LNAV/VNAV with raw data back-up reference, subject to RNP & ANP being correct. Thus the aids need to be working. Amazingly, because it happened to me, even on my IRS/GPS equipped a/c our MEL stated that 2 VOR's, 2 ILS's and 1 ADF & DME was required for IFR controlled airspace operations. I was shocked. A re-set of the CB solved the problem, and I notified FLT OPs if this could really be correct. No reply.
A further question about the SOP to check the ANP/RNP on approach, and what to do if it was outside limits, also went un-replied. Common sense says you can not use LNAV/VNAV, but the youngsters asked the question. If you have to check something as an SOP to be allowed to use it they wanted an SOP of what to do if it was bust. Trained robots, but there we are.

[Phil Squares]

RAT5,

I guess I don't quite know what you are asking.

In my world a BRNAV would never be accomplished. It is, after all, a Basic RNAV approach. I don't think that was the question.

I qualified my response. Assuming Dual FMC operation with GPS/GPS updating the procedures I have flown under (FAA, SE Asia and ME), as long as your ANP is getter than the RNP there is no mandatory monitoring of raw data. Also a NDB is not required for entry into controlled airspace. Our aircraft don't even have then and we are authorized to fly NDB approaches.

If you are going to fly a NP approach and the ANP does not meet the RNP requirements, then of course you would have to fly the raw data. But, how often does that happen. IIRC, after the last GPS/GPS update, the ANP will be better than RNP for some time. Even in the "old days" without GPS updating I flew the 320 with no NDB installed and we had no mandate to crosscheck raw data.

Again, do we do hard tune the navaids on departure or arrival or even enroute????

[RAT 5]

Thanks Phil. It seems you are outside EU. Hence my 'inside EU' Ops MEL required an ADF etc. Plus my CAA required all nav-aids associated with the approach to be serviceable. It did once come to a conflict where it was an ILS/DME promulgated approach. The DME was U/S. OK this is not an FMS/NPA approach, but the DME was required. It was not a VMC day. We used common sense and managed to achieve a 'radar fix' for the TOD. However, for NPA's all aids need to be serviceable. Such is the way of life in our neck of the woods.