:D:D:D:D:):):D:D:D

Disregard.....

They are on their way. I've seen the drafts. Useable, but VOR tolerances are much better..

They're still using the 727 for ATPL flight planning and performance and loading exams! LOL!

BTW, I thought some modern airliners use enroute Nav Aids to update their FMS position? Or can they do without these enroute updates?

TrainingWheels,
The way I understand it (disclaimer, I operate an aircraft with an FMS, however other FMS's could be different), is that the FMS updates its position mainly using the inbuilt GPS, and then uses VOR and DME in the event that the GPS stops working. However, there is also a way to tell the FMS which one you want it to update exclusively by (ie. if for some reason you want it to stop using the GPS, then just select VOR and DME).

I think I just confused myself writing that, so might be back to the book to update myself on exactly how it works, but that's basically the gist of it.

morno

Ok, thanks morno ... I remember reading about this for ATPL systems but that was years ago.

Hi, training wheels. This is an excerpt from a typical FMS setup for a modern airliner:
GPS is Primary if GPS is used as the primary source of navigation by the FMS. This happens on long oceanic flights where ground navaids are not available. If GPS is unavailable for whatever reason, the FMS will display a GPS downgrade message and you will have to rely on available navaid signals to quantify the position error of the FMS. In this case you should not rely on the FMS data for an approach and you would probably seek vectors and fly raw data based on ground navaids for greater navigation accuracy.

Thanks RF for the info .. it's a alot more sophisticated than than the UNS 1K FMS we use in our aircraft ..

They are not essential, but some of the are very very useful. Under the separation standards we use NDB's are more accurate than GPS under some circumstances. Also passing over a VOR/DME allows us the "reset" the nav tolerances of aircraft with IRS.

Wouldn't they have IRS? Admittedly that only covers en-route, but people flew non navaid routes long before GPS.

ReverseFlight thats interesting. The way I read that, GPS Primary averages three IRS and the GPS position and ignores navaids. Without GPS Primary, it averages three IRS positions and a radio fix, and adds GPS only if the GPS position agrees. The difference seems to be the trust in the GPS position. Is GPS Primary selected by the crew or the FMS?

Have ASA spoken to CASA about getting rid of VORs and NDBs?

To quote CAAP 179a

'4. If a TSO-C129 or C129a receiver is used at any time, or a C145a or C146 receiver is used during a period when FDE is not predicted to be available, an alternate visual approach or instrument approach based on NDB or VOR must be planned.'

Looks like the end of 129's for IFR use and very bad luck if you arrive with a 146 needing an approach when there is a RAiM outage.

There seems to be a lot more 146 fault detection outages than for 129's. Then a 146 becomes a 129 anyway.

Also,

'Automation Induced Complacency
The highly automated nature of navigational calculations using GNSS provides significant benefits including increased reliability, accuracy, proficiency and system monitoring ability. However, it can be difficult to stay alert and detect gross errors when monitoring automatic equipment. The operators’ continuing experience of highly accurate positioning information from GNSS can lead to the assumption of infallibility promoting a complacent attitude resulting in decreased crosschecking of the system.'

Well, that's alright now then... Let's just get rid of VORs and NDBs because we dont now need anything to crosscheck against anyway.... :ugh:

I refer you again to NPRM 1105AS, a CASA document.
This is the driver behind any decommissioning.

casa, icao and confusion with navigation
 

From the NPRM:

Civil Aviation Safety Authority - NPRM 1105AS


and:

and the big metal:

and:

How's that for creating more confusion between OZ and ICAO requirements - Bring on the next audit!!

Shutting down NDBs
 

On a related note, if NDBs were to be decommissioned, would GPS be allowed to be used in-lieu of NDBs?

I am in a situation where I am unable to do the SID out of YPJT due to not having an ADF, and have been told that GPS was in the pipeline to be approved in lieu of, then subsequently told that was not going to happen.

Given what I have heard/read, GPS is probably more accurate than NDB anyway?

I'd looked into getting an ADF a few years ago and was advised not to bother as NDBs were going the way of the dodo, that was back then...

Same with getting an HF - same mob suggested an installed satphone was the way of the future...

QFF, in short....no. GPS won't be allowed in lieu of NDB as a blanket change. The protection areas are too different. In order for that to happen the ndb procedure will have to be re assessed using GPS protection areas.

It's more than GPS being more accurate. It may be more accurate, but how do you know when you are getting that accuracy? It's for this reason the protection areas are a little larger than those for ndb.

Alpha

Check your RAIM prediction before flight. I suspect (only theorising here) that CASA is happy provided RAIM is predicted to be available. Perhaps, after that, if one sat then falls over, RAIM will still be available?

Because it's a TSOed system. Apart from the alternate requirement, the same GPS that could easily navigate QFF on the Mantl 1 would be used to take him to within 400ft of the ground, sight unseen, out in the boondocks (assuming it's a GPS NPA kit).

The system being TSO'd only means it will perform within certain accuracy limits as specified in the TSO. There is know way to know how the system is performing within those limits, like RNP can. So basic GPS protection areas have to cater for the worst performing TSO'd system.

A system being TSO'd has nothing to do with accuracy alone, more to do with accuracy vs performance

Yes I agree that QFF could navigate the Mantl 1 with the same perceived accuracy. And 90% of the time that might be the case. But protection areas are based on 3SD containment (99.7%) and on paper the figures reveal a wider protection area is required.

Admittedly, USA uses TERPS, not PANS-OPS, but they didn't seem to have a problem with GPS overlay approaches. GPS guidance was essentially used to track an NDB or VOR approach.

Different concept. I don't believe you can fly a GPS overlay approach without monitoring the navaid for the approach. Eg you can fly an ndb approach using GPS overlay, provided the navaid is tuned, identified and monitored for the approach. At least that's how I'm led to believe it is done. What QFF wants is to be able to fly the ndb procedure using only GPS in lieu of the ndb when the ndb gets switched off.

Without work done to re assess the approach, this won't happen.

Alphacentauri - thanks for your replies - that makes sense.

So I guess in the wider scheme of things, shutting down navaids would save money in the longer term but those savings might be diminished by having to have procedures re-surveyed/re-designed to different standards...

It may be cheaper to keep the damn things going...