Airways/Fixes

[Boslandew]

I last flew in 1998 when I retired holding an ATPL/H IR. I have had little direct contact with aviation since.

I have just seen a modern airways chart and noted the vast difference between that and an old one from 1998. Am I right in thinking that airways and fixes are no longer necessarily defined by VOR/DME or NDB's but may be defined simply by Lat/Long?

If that is so, presumably GPS is now a primary navaid. If so, are VOR/DME/ADF used for anything other than approaches.

Thank you in advance for any information.

[rudderrudderrat]

Hi Boslandew,

Some airways routes are still defined by VOR & DME, other RNAV routes (Lat & Long) don't need to have VOR defined radials.

Most of us now fly using RNAV. Any airways VOR is automatically tuned & can be displayed. We are still doing NDB / VOR approaches - so most of it would still be obvious to you.

Loran, Consul & Decca have gone.

[Denti]

Basicly its all RNAV now (doesn't have to be GPS). Even when we fly VOR or NDB approaches we do it via database points and do not even need to monitor raw data (provided two independent FMC are installed), however i think it is still good airmanship to do so, after all i just need to press one button to see it on the screen anyway.

I haven't used any VOR or NDB really in the last few years, however in our old 737 classics we had to check NDBs in russia where we lost ANP over time due to the lack of DME stations, in those birds RNAV was done without any GPS mainly with automatic DME/DME updating. They're gone now and in the NG its dual GPS and usual ANP values hovering around 0.02 to 0.04 NM.

[Boslandew]

Gentlemen

Many thanks for the info. Aviation certainly has moved on in ten years. I had assumed that RNAV meant GPS and had no knowledge of DME/DME fixes. I'm not too sure how they would work so must do some research.

Interestingly North Sea nav, (I'm ex BAHelicopters, mainly S61 and the commercial Chinook) was all RNAV using Decca either with the moving map or with Danac where we had ten whole waypoints to use. About '95 we moved on to GPS but only as a secondary aid. IBC's in the sim were of course all airway-based, allsame as fixed-wing.

Not surprised to hear that Loran and Consol have gone. During one interminable North Sea leg I once managed a Consol fix, plus or minus 20 miles.

Can I have just one more query. My interest in RNAV comes about through the gift of X-plane simulator for my Mac. Could you tell me what a typical rate of climb might be for, say, a 737 on take-off, also during a standard climb on the airway and a standard descent

Once again, many thanks for the response, I'm obliged to you.

[bfisk]

The concept of RNAV (Area navigation) and RNP (Required Navigation Performance) is certainly the way forward, and is already implemented worldwide, to various degrees.

The very short explanation is that a RNAV system is an indepentent, onboard system for navigation, which may use several sensors depending on the aircraft configuration. Sensors may be one or more INS/IRS's, GPS, and a combination of conventional navaid fixing using VOR/DME/LOC, with the most accurate normally being DME/DME fixing. The RNAV system will monitor the integrity of it's position by giving you an estimated ANP -- Actual Navigation Performance, which should be lower than the RNP. Ie, for a Basic RNAV system, BRNAV, which is required a lot of places (in Norway over FL95, and in certain TMAs over FL45 for instance), the the required navigation performance is RNP5 -- ie the RNAV system needs to keep you within 5NM of the indcated position for 95% of the time. Quite crude, that is. However more and more procedures are now designed for Precision RNAV, PRNAV, which has a RNP value of 1 nm. ANP will normally be significantly better in areas where plenty of conventional updating/fixing is avaliable. It is envisaged that as technology progresses, procedures using even lower RNP, such as RNP0.03, to maximise airspace use and efficiency.
:)

[Denti]

Hi Boslandew, bfisk explained RNAV pretty well another point to learn more about it is EUROCONTROL Navigation Domain - Home (http://www.ecacnav.com/) the eurocontrol domain about RNAV and RNAV applications.

About your question to the 737, a lot depends on variant, weight (load factor, fuel) and to some extent on SOPs. Usually a take off is done with reduced thrust and pretty every time with reduced climb thrust as well. After the third segment typical climb rates are between 2500 and 4500ft initially, however those will reduce as you climb, if heavy sometimes doing the last few flightlevels will be very slow indeed. Descends are usually done with idle thrust and initial descend rates can be quite high. Speeds for climb and descend depend on cost index, in todays economic climate it is often quite low and the speeds slow.

A good place to learn more about the 737 is smartcockpit (google it) and The Boeing 737 Technical Site (http://www.b737.org.uk).

[bookworm]

In principle, an airway prefixed with A, B, G or R can still be flown with conventional navaids. L, M, N, W, Y Z rely on RNAV.

[Boslandew]

Gentlemen

Many thanks indeed for your time and information - its like a potted master-class in airways flying. Bfisk's summary gives me a much better over-view of modern nav and I found the web-sites suggested a mine of information.

Bookworms comments make much more sense of the airways chart I have just acquired.

I was amazed at the ROC/ROD's you mention, Denti. I had guessed at a max climb of 2000ft per min and to find that it may be more than twice as much is a real surprise although I appreciate that it will decrease with altitude.

I really am obliged to you, I now have a far greater understanding of modern nav. To me this is what PPrune is all about.

[5LY]

Just to expend slightly on that, it's the FMC position which is being refined from all of the inputs described above. It likes GPS best, then DME/DME and so forth. It's constantly comparing and refining the pos. It navigates, then using the derived pos. The pilot interfaces with the FMC through his CDU and tells the system where it's to go, but the heavy lifting is all gone now. Even on non prec. approaches now you use the FMC to fly the approach and do a cursory monitor of raw data as a gross error check.

[Boslandew]

It sounds about as good as it could get. Presumably you have a data base of all waypoints/fixes in Europe? and can also select pre-planned routes?

How have the IR and IBC's changed as a result? Are you still required to do raw ILS's and NDB aproaches.

In practice, are you ever put into the hold these days?

Makes me wish I was back on the flight deck!!

[5LY]

Most everyone does Non-prec. on checks as you would do them on the line, using the FMC and vnav. They're very easy to do if done right but can easily be screwed up - garbage in garbage out, so practise is required. Different completely than flying the needles, but much more accurate. Vnav gives a constant rate of decent to the runway, so no more dive & drive for most of us. (There still are some dinasours about).

The hold? Yes. Pretty regularly. Again done with the magic.

Be careful what you wish for. Much rather be fishing with beer in hand.

[Denti]

Until last year we had to do a raw data single engine ILS every 6 months during the usual check, however since then training has changed and we don't have to do it anymore, it wasn't any regulatory requirement anyway. Raw data non precision approaches are not done at all, however "raw data" became easier with the new fangled IAN thingy which presents any kind of approach the same as an ILS. Personally i try to fly raw data approaches as often as i can, however i have to take care not to overload my captains so it does depend on the situation.

[Boslandew]

Back in the 70's-90's of my experience, it was all by the needles, ILS into ABZ, NDB approaches to the rigs, I even managed a VOR approach to Kirkwall in the Orkneys once.

One exception was Penzance where I spent my last five years happily flying to the Scillies. Into Scillies it was a Decca approach backed up by the NDB at St Mary's. Into Penzance it was quite the most complicated approach I've ever seen. It started with a VOR/DME fix and was carried out following a Decca track on the moving map with the final leg flown heights against distance to run. To be valid it required VOR and DME cross-checks at all salient points, final track checked against the NDB at PZ heliport, the rad alt and finally, Penzance swimming pool, very prominent on the Mounts Bay coast, had to be identified on the ac radar. Six of those in a morning at each end and you knew all about it.

What we wouldn't have given for an FMC (had we known they existed)

The beer and fishing, I have to admit, is fun, reward for a virtuous life I always say, but it would be nice to see how its done today.