VOR/NDB usage on IFR flights

[BackPacker]

Proud owner of a PPL and I'm now trying to get the NQ. For legal reasons (NVFR not allowed in the Netherlands) the night flights will be done on an IFR flight plan, with an IRI on board etc. There is an agreement with the authorities in the Netherlands that if I can fly the plane without the instructor having to take control, those SPIC hours/landings may be counted as if they were flown solo so count for the solo portions of the NQ. The stop-and-gos will be done in Antwerp, Belgium, who allows NVFR and visual circuits at night (till 2000 local).

Nevertheless, for all practical purposes it's going to be an IFR flight: SID, en-route, STAR, ILS etc. I've been studying the plates, flown the flight in MSFS already and although I understand the principles of VOR/NDB navigation, I have a bunch of practical questions.

Oh, and the plane we're taking most likely won't have GPS, just 2x VOR (one if which which has GS as well), 1x ADF, 1x DME: S/S in flightplan terms.

First question. I need to fly via a bunch of intersections. I cannot always find how these intersections are defined, other than lat/long, but I guess most of them have VOR/DME or VOR/VOR references as well. If you fly to such an intersection on a VOR radial, I have seen that some intersections are defined by VORs sometimes 60 miles away. This means that a small OBS ring setting error or calibration error, even if only one degree, might mean you miss the intersection by miles. How serious is this in practice? Is there a circle of uncertainty or something that ATC understands about?

Second, I've never flown IFR so far but when listening in to IFR R/T I regularly hear that IFR flights are taken off the SID/route/STAR for some reason, and later on told to proceed to an intersection or beacon "direct". If you get a beacon "direct", that's easy. But how do you fly to an intersection "direct" if it's not a beacon? Do you set a guestimate course and then "bracket" it by monitoring both the VORs (or the VOR and DME arc) that define the intersection? Or does ATC take into consideration that you do not have GPS/RNAV and therefore do not offer you a "direct" to an intersection?

Third, I will have two NAV receivers. Is there a specific way of using them? So far, in MSFS I've tried to use NAV1 for the radial I'm actually flying on (or the ILS), and NAV2 to either the crossbearing that defines the intersection, or the next radial to pick up. Is this the correct way of doing things or are there other recommendations?

Last, I have seen approach plates where they include something which I guess is a "procedure turn" to intercept the ILS: From overhead the field (or overhead a VOR/NDB close to the field) you fly outbound a certain number of miles, make a standard turn onto a heading, and then this heading should coincide with the final approach course. However, when I did this in MSFS, in the 100 knot C172, a standard turn has such a small radius that I was on the final approach course way to early, two to three miles offset from the final approach path. I understand that the procedures are designed for aircraft with a higher speed than a C172, so how do you solve this? Do you fly them at half rate, or do you stop turning 30 degrees or so before the final approach course, and thus intercept the ILS or VOR? Even though the plates do not specify an intercept?

[llanfairpg]

First question. I need to fly via a bunch of intersections. I cannot always find how these intersections are defined, other than lat/long, but I guess most of them have VOR/DME or VOR/VOR references as well. If you fly to such an intersection on a VOR radial, I have seen that some intersections are defined by VORs sometimes 60 miles away. This means that a small OBS ring setting error or calibration error, even if only one degree, might mean you miss the intersection by miles. How serious is this in practice? Is there a circle of uncertainty or something that ATC understands about?BP in my experience ATC are not so tolerant of errors these days due to the large amount of operators using FMS amd FMGS systems. We were one of the last operators of clockwork instrumented nav aids across the North Sea from the UK and ATC were always a bit concerned about our accuracy!!! The basis of the airway systym was a 10 mile wide corridor so if your are within that there should be no problem. I once flew with a captain who used to delight in turning onto a new heading around 5-6 dme before any VOR stating "well I am still in the airway so so what!" (in fact thinking about it some FMS/FMGS systyms do exactly that too)

In regard to your other query the intercept heading you choose is your choice and yes the charts are drawn for a much faster speed, try speeding up, if I can fly a 120 kt approach into LHR in a C172 you should be able to manage it on a procedure turn! Save you money too!

Second, I've never flown IFR so far but when listening in to IFR R/T I regularly hear that IFR flights are taken off the SID/route/STAR for some reason, and later on told to proceed to an intersection or beacon "direct". If you get a beacon "direct", that's easy. But how do you fly to an intersection "direct" if it's not a beacon? Do you set a guestimate course and then "bracket" it by monitoring both the VORs (or the VOR and DME arc) that define the intersection? Or does ATC take into consideration that you do not have GPS/RNAV and therefore do not offer you a "direct" to an intersection?

When you file a FP your nav equipment is on that but tell ATC you cannot accept that routing just say, " request routing too xxx beacon.". Or can you vector me for xyz intersection.

[mm_flynn]

In real life IFR there is an assumption you have RNAV/GPS (and a requirement to have it above FL95). Being RNAV equipped I have no experience of Eurocontrol handling of flights filed without RNAV, however, long ago in the US all my IFR work was done on basic instruments. So to your questions.

1 - The airways structure assumes you have RNAV, but you will find most SIDS and STARS have points clearly defined by radio aids. I would expect also that you can find enough low level routes that are defined by radio aids to get you through your training.

2 - ATC should not clear you direct to a point in space intersection if you are not RNAV equipped.

3 - Tracking your current radial on NAV1 and setting up NAV2 to display the radial defining the intersection or the new airway track would be a sensible way of doing it.

4 - The procedure turn is likely to have several different outbound headings or distances to reflect the different speed classes of aircraft A=slow to D=fast. If you are flying the A distance/course it should work. If you wind up too tight, stop turning 30 degrees prior to the final course and intercept the ILS or VOR course.

[Islander2]

I understand that the procedures are designed for aircraft with a higher speed than a C172, so how do you solve this?Just a thought! I'm sure you haven't missed this, but ....... you are checking the Cat A,B procedures, are you? The Aerad charts I use are drawn for Cat C,D procedures and only give the appropriate Cat A,B tracks, dme's and timings in the notes.

[IO540]

First question. I need to fly via a bunch of intersections. I cannot always find how these intersections are defined, other than lat/long, but I guess most of them have VOR/DME or VOR/VOR references as well. If you fly to such an intersection on a VOR radial, I have seen that some intersections are defined by VORs sometimes 60 miles away.

Some intersections are VOR/DME. But many are purely RNAV and the only way you can hack those is with a GPS.

Legally you need BRNAV capability anywhere above FL095 in Europe but IME ATC aren't that clever and they treat everything as an RNAV waypoint. They will send you to a VOR 200nm away without a thought. All the stuff about navaid DOC (documented operational coverage) is meaningless nowadays. RNAV is assumed - end of story.

This means that a small OBS ring setting error or calibration error, even if only one degree, might mean you miss the intersection by miles. How serious is this in practice? Is there a circle of uncertainty or something that ATC understands about?

I have never tried this - always fly with an IFR GPS. I guess "a few miles off" would definitely be noticed.

Second, I've never flown IFR so far but when listening in to IFR R/T I regularly hear that IFR flights are taken off the SID/route/STAR for some reason, and later on told to proceed to an intersection or beacon "direct". If you get a beacon "direct", that's easy. But how do you fly to an intersection "direct" if it's not a beacon?

That's an old question ;) You can't. Actually there are ways to hack a sort of direct track to an RNAV waypoint, using two VOR receivers, but only a masochist would try it. And it's sloppy and inaccurate.

In Europe, STARs are very rarely flown to major airports. The traffic is radar vectored. SIDs are flown fairly often but even then radar tends to take over soon and starts to vector you around.

What is important is that you understand the vertical and horizontal parts of a clearance. They are separate. Get your IRI to explain that. Some of it is quite subtle. E.g. you can be cleared for a STAR, which shows various levels for different parts of it, but if ATC has also given you a level you have to fly that level instead - until further notice. Same with SIDs - often you get a SID, and ATC gives you climb instructions which are way different to what the SID says - but you stay on the SID laterally.

But once they give you a vector, the SID or STAR goes out of the window and you fly the vector laterally, and the most recent vertical clearance vertically.

The SID or STAR also needs to connect to your filed route :) Sometimes you can get a SID/STAR belonging to another plane....

Do you set a guestimate course and then "bracket" it by monitoring both the VORs (or the VOR and DME arc) that define the intersection? Or does ATC take into consideration that you do not have GPS/RNAV and therefore do not offer you a "direct" to an intersection?

RNAV is simply assumed by ATC. You can however say you have no RNAV capability - I had to do that once on a GPS failure - and request vectors or VOR navigation. Then they will wake up and give you a nice VOR-VOR route.

Third, I will have two NAV receivers. Is there a specific way of using them? So far, in MSFS I've tried to use NAV1 for the radial I'm actually flying on (or the ILS), and NAV2 to either the crossbearing that defines the intersection, or the next radial to pick up. Is this the correct way of doing things or are there other recommendations?

There is no standard. I would use NAV1 for the track to the navaid (especially as NAV1 tends to drive the CDI in your primary field of view, e.g. an HSI) and use NAV2 for the cross-cut. But a DME is vastly better for cross-cuts, and most European VORs have a co-located DME (not in France!). The problem with using a VOR for the cross-cut is that if you don't pay attention you can fly through the cross-cut and it isn't obvious afterwards. Never create extra work for yourself, and always choose a method which avoids ambiguity.

Last, I have seen approach plates where they include something which I guess is a "procedure turn" to intercept the ILS: From overhead the field (or overhead a VOR/NDB close to the field) you fly outbound a certain number of miles, make a standard turn onto a heading, and then this heading should coincide with the final approach course.

Yes, that is standard European (old) procedure design. It's obvious that (with a GPS) you could just fly to the localiser/VOR radial and intercept directly. But in the old days (when boys were boys, girls were girls and life was real) there was no RNAV capability - one could only fly between radio beacons - so the pilot would track to the overhead, usually an NDB, watch the ADF needle flip over 180 degrees (this "overhead flip" is the only bit of an ADF that is accurate), then fly the outbound and come back in, and there is generous terrain clearance on those two legs.

However, when I did this in MSFS, in the 100 knot C172, a standard turn has such a small radius that I was on the final approach course way to early, two to three miles offset from the final approach path. I understand that the procedures are designed for aircraft with a higher speed than a C172, so how do you solve this? Do you fly them at half rate, or do you stop turning 30 degrees or so before the final approach course, and thus intercept the ILS or VOR?

The latter :) Always fly a positive intercept to the inbound track. That's how one flies an ILS. Fly an NDB or VOR approach the same way.

I've sent you a PM to an article on IFR in Europe.

[BackPacker]

you are checking the Cat A,B procedures, are you?

Sure. But even the cat A turn was way too big for a standard turn at 100 knots. I eventually figured things out but intercepted the localizer waaay above the glideslope. Took a lot of manoeuvring to get sorted. Would've been seriously unsafe if it wasn't done in MSFS but for real... :}

This was EBAW ILS 29 by the way. Outbound from the VOR (located at the field) at 096 degrees, right turn at 6 DME, intercept the ILS 291 degrees at 6 DME again (IF), start descend (FAF) at 4.6 DME. Not a lot of time for correction.

[BackPacker]

Some intersections are VOR/DME. But many are purely RNAV and the only way you can hack those is with a GPS.

Thanks for that. Somehow I always feel like cheating when using a GPS, particularly when I'm trying to learn something from a flight, wanting to do things the "proper" way. Good to hear that GPS is sometimes the "proper" way to do things nowadays. Still, not all our IFR capable aircraft have GPS, let alone an IFR certified GPS. The only plane that has everything is the DA-40 which is still down waiting for parts.

(BTW I understand that technically GPS is just one of several RNAV technologies. But is there anybody out there, except maybe a bunch of older airliners with INS, that uses an RNAV technique other than GPS?)

[IO540]

Legally, on an IFR flight plan, you need BRNAV capability above FL095, in general.

This can be done with

- an IFR (BRNAV certified) GPS

- an inertial nav system (airliners use those)

- a "VOR relocator" like the old KNS80; this receives a VOR and a DME and creates a fake VOR/DME which is elsewhere and you can track directly to it. 2 problems: KNS80 is not FM Immune, and both the real VOR and the real DME have to be receivable. Most people use a KNS80 as a door stop. You can overcome the FM problem with an antenna filter, and you can even get a KNS80 installation BRNAV approved. But you would never do this from new.

The key thing is that like I said, ATC treat their whole universe as RNAV waypoints, and will happily throw any waypoint at you. If you don't recognise it (it "should" be on your filed route, and therefore on your plog) ask them to spell it. Then dial it up as a DCT in the GPS. And sit in silence for the next 30-60 mins :) IFR is great when enroute.

[llanfairpg]

If none of all the above works try talking with an American accent

[IO540]

If none of all the above works try talking with an American accent

No, that helps only if you are not 8.33 equipped and ask for a climb FL350 :)

[llanfairpg]

I heard a German controller say to a Pan Am flight many moons ago;

"Vie are you 6 miles south of the centreline (airways) Pan Am xyz."

Long pause.

"sheer incompetency Mac"!

[moggiee]

Sure. But even the cat A turn was way too big for a standard turn at 100 knots. I eventually figured things out but intercepted the localizer waaay above the glideslope. Took a lot of manoeuvring to get sorted. Would've been seriously unsafe if it wasn't done in MSFS but for real... :}

This was EBAW ILS 29 by the way. Outbound from the VOR (located at the field) at 096 degrees, right turn at 6 DME, intercept the ILS 291 degrees at 6 DME again (IF), start descend (FAF) at 4.6 DME. Not a lot of time for correction.
A nice, solid 45º intercept onto final approach track helps - it gets you settled as early as possible.

[mm_flynn]

Sure. But even the cat A turn was way too big for a standard turn at 100 knots. I eventually figured things out but intercepted the localizer waaay above the glideslope. Took a lot of manoeuvring to get sorted. Would've been seriously unsafe if it wasn't done in MSFS but for real... :}

This was EBAW ILS 29 by the way. Outbound from the VOR (located at the field) at 096 degrees, right turn at 6 DME, intercept the ILS 291 degrees at 6 DME again (IF), start descend (FAF) at 4.6 DME. Not a lot of time for correction.

Try it again, I suspect something wasn't set up correctly or your turn was at more than standard rate (look at your flight track in the sim). I looked at the plate (and have flown it for real but from the hold rather than the procedure turn) and it should work perfectly at 100 kts.

If you fly it exactly as the procedure with no wind you would roll out about 0.3 miles to the right of the localizer at 6 dme with 1.5 miles to run before GS intercept - about 60 seconds at 100 kts. (So only a small intercept leg on the turn would be required to be bang on)

[BackPacker]

If you fly it exactly as the procedure with no wind you would roll out about 0.3 miles to the right of the localizer at 6 dme with 1.5 miles to run before GS intercept - about 60 seconds at 100 kts. (So only a small intercept leg on the turn would be required to be bang on)

I tried it again yesterday and ended my turn with a 30 degree intercept. Worked much better although I don't remember exactly how long the intercept leg was. But in both cases, looking back at the sims track log, I noticed how incredibly tight my turns were, despite the fact that they were rate 1 turns at 100 knots. Nowhere near as wide as the approach plates suggest, even for a cat A at 100 knots. And the same thing happened on SIDs as well. Maybe an MSFS thing, I don't know.

Tonight, if everything goes well, it's for real. But most likely we'll get "vectors to the ILS" and that's just fine with me.

[IO540]

This is normal, BP. The plates are drawn for much faster aircraft.

[mm_flynn]

The specific plate has an outbound procedure leg of 96 vs 291 inbound (only 15 degrees over 6 miles) it is fine at 100 kts. I suspect MSFS is not actually giving appropriate rate 1 indicator (or it is not being flown). Try a 360 at rate one and see if it takes 2 minutes.


In real life that approach is fine - although my planned departure was a disaster. Severe clear downtown and the airport so fogged in I needed the follow me truck to get from where I had shut down to the hangers for the night --even then only the flashing lights were visible at 50 feet (never seen such dense fog)!!

[moggiee]

I tried it again yesterday and ended my turn with a 30 degree intercept. Worked much better although I don't remember exactly how long the intercept leg was. But in both cases, looking back at the sims track log, I noticed how incredibly tight my turns were, despite the fact that they were rate 1 turns at 100 knots.
As I said earlier, a 45 degree intercept will be much better - especially off a "teardrop" procedure (which very often puts light aeroplanes too wide for comfort).

[Contacttower]

Maybe an MSFS thing, I don't know.



For practicing IFR work (at c.100kts) I've actually found MS FSX very accurate...with the 'CAT A' labeled turns working reasonably well in say the Piper Archer sim.

[smith]

Point to point navigation, imagining lines and angles on the OBS. Thats how we found a point in space when I did my IR. Not that accurately mind you.

[BackPacker]

Well, did it. Didn't get a "direct" to an intersection, only "direct" to beacons. And obviously got taken off the SID and STAR as soon as ATC found it convenient - although we did fly the procedure teardrop turn at EBAW for ILS 29 and the 45 degree intercept worked fine. But with upper winds from the side at 30-odd knots at altitude tracking to/from an NDB, and the instructor requesting the "VOR/DME 06 approach, circle to land 24" with winds being 230/19G25 or so at the end of the flight, this evening was very interesting anyway....

I have found new respect for all you IFR rated pilots out there. And a new challenge, perhaps in a few years time.

Anyway, thanks for all the answers. I learned a lot from you guys, and a lot from this flight.

Oh, and I brought my Petzl "tactikka" which I normally use for, you guessed it, backpacking. It's a headlamp with 4 white leds which can be set to three brightness settings, and a flip-in-front red filter to preserve your night vision. The instrument lighting on the plane wasn't that good, and the Petzl proved invaluable. Even the instructor had never seen something like it but asked where you could get them (outdoor shops). I highly recommend it!