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Question: An aeroplane is travelling away from an NDB on a track of

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Question: An aeroplane is travelling away from an NDB on a track of

Old 16th Nov 2018, 19:13
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Question: An aeroplane is travelling away from an NDB on a track of

An aeroplane is travelling away from an NDB on a track of 145° with 5° starboard (right) drift. The relative bearing indicator (RBI) should indicate a bearing of:
Answer: 185° relative
Can anyone explain why please? Ideally with a picture. I tried to emulate the problem with this RBI emulator but couldn't figure it out.
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Old 16th Nov 2018, 20:04
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The track isn't a red herring, although TA's explanation is probably simpler in this case (constant track to / from the NDB).

Magnetic Bearing - Magnetic Heading = Relative Bearing

As you are flying a TRACK of 145° from the NDB, the MB to the NDB is the reciprocal of 145° = 325°

As TA has said, there's 5° right drift, so your HEADING is 140° to counteract the drift.

Therefore RB = 325° - 140° = 185°
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Old 16th Nov 2018, 20:14
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The track away from the NDB is irrelevant, the RBI display would be showing 180 degrees if there was no drift. As there is a 5 degree drift to starboard, this will be added to the RBI indication, giving the 185 degrees relative bearing in the answer. Please excuse the rather crude drawing, best I could do with the limited drawing package....
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RBI Display.pdf (2.5 KB, 76 views)
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Old 16th Nov 2018, 22:51
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The track of 145º from the NDB is, indeed, entirely irrelevant. If you are maintaining a constant track - any constant track - away from the beacon with 5º right drift, the RBI needle will point to 185º relative. Mind you, I don't think I've ever used an RBI since I did my initial IR, when I used one coupled to a 'coffee grinder' ADF and a DME that would only tune X channels. Ah, De Havilland!
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Old 16th Nov 2018, 23:12
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An observation about outbound NDB tracking from my IR days. One of the NDB approaches that I used to practice, had the NDB at the IAF, 4.2 nm from the threshold. I always found outbound tracking very difficult, until one day my instructor suggested "Once you have tracked to the NDB and have station passage, don't change your heading. You'll be close enough to the runway when you reach your missed approach time." It worked very well.
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Old 17th Nov 2018, 09:42
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Another observation about outbound NDB tracking from my IR days. I've never understood why they taught NDB tracking using that stupid "push the head, pull the tail" business. An RBI is a really simple instrument and you only need one rule whether you're tracking to or from a beacon: "Steering track plus X, looking for track minus X" (or vice versa) where X is your drift angle. If the arrow's pointing to the right of your mark, it's a fly-right indication, if it's pointing to the left, fly left.

In the OP's example, the track is 145 degrees and the heading is 140 degrees, so the rule is "Steering track minus 5, looking for track plus 5".

If you're tracking to the beacon, in still air the arrow should be pointing at the 360 deg mark. "Steering track minus 5, looking for track plus 5". So to be on course the arrow should point at 005. If the arrow is right of 005, it's a fly-right indication and vice versa.

If you're tracking from the beacon, just keep looking at the arrow. In still air the arrow should be pointing at the 180 deg mark. "Steering track minus 5, looking for track plus 5". So to be on course the arrow should point at 185. Just as before, if the arrow is right of 185, it's a fly-right indication and vice versa. Maybe you get a fly left indication and decide to increase the drift correction to 15 degrees to get back on track. "Steering track minus 15, looking for track plus 15" - so when the arrow points at 195 degrees, you're on track.

Incidentally, this exact same rule also works for things like passing abeam the beacon in an NDB hold. You steer your outbound heading, with perhaps a total of -20 degrees of drift correction from the outbound track. In still air you'd be looking for the 90 (or 270) degree mark. "Steering track minus 20, looking for track plus 20". When the needle passes the 110 (or 290) degree mark, you're abeam.
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Old 17th Nov 2018, 11:14
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^This, works for me every time. Have you read 'VOR, ADF and RMI' by Martin Cass? That and practise on MS Flight Sim did it for me.

Though the last time I flew an NDB approach in real IMC was a couple of years ago now, on Project Propeller, at Shoreham. But it’s a skill worth preserving.
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Old 17th Nov 2018, 19:19
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Tim you have access to the best ADF I have ever had the pleasure to fit to an aircraft, the loop swing was as close perfect as I have ever seen............... forget the GTN650 keep those old timeskills alive !
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Old 17th Nov 2018, 22:48
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I could never get my head around the Mary Had + Roast Beef = Mary Barfed during my IR training, thank god there was only 2 questions on the written and I didn’t have to shoot an NDB approach.

My advice, ditch the ADF and free up some panel space for a fancy new solid state toy! and just sit back and follow the magenta line.


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Old 17th Nov 2018, 23:33
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My advice, ditch the ADF
How can you say that? I suppose you'll be suggesting they should get rid of the four-way range next?

It's just about impossible to find a functioning NDB approach in the US now. I think the nearest one to here (SF Bay Area) is 200 miles north at Siskiyou County. And that of course has an official GPS overlay. Even the VOR approaches are disappearing rapidly. When you can fly an LPV to ILS minima, what would be the point?
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Old 18th Nov 2018, 00:04
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The last NDB approach I shot for real in IMC without some sort of GPS track guidance was 1994. The technology is 90 years old and ground stations are disappearing rapidly, I don't understand why this is still being taught.
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Old 18th Nov 2018, 07:26
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I was once told that old Soviet procedures used 2 NDBs aligned with the instrument RW. With 2 x ADF receivers and a twin needle display, all the pilot had to do was to turn to keep the needles aligned. After passing the 'outer', the indications became even more intuitive - same after passing the 'inner'. Cheap and simple - if the pilot had been properly trained and was in current practice.

But 2 x ADF receivers were essential for this type of procedure. In 1996 a US CT-43 crashed whilst attempting the procedure with only 1 receiver - see https://en.wikipedia.org/wiki/1996_C...AF_CT-43_crash .
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Old 18th Nov 2018, 10:34
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In the good old days we did IR renewal in the B767 sim under these conditions:

no autopilot
no autothrottle
no FMCs
raw data on HSIs
PF to make RT calls (including ETAs for next waypoint)

I used to brief crews under check: 'this is completely unrelated to real life but it'll keep your scan up to scratch and boost your confidence in your ability to hand fly in IMC should the need arise.'

Originally Posted by India Four Two View Post
my instructor suggested "Once you have tracked to the NDB and have station passage, don't change your heading. You'll be close enough to the runway when you reach your missed approach time." It worked very well.
Many pilots found interpreting the ADF needle when tracking away from the NDB on final approach difficult. But with raw data (including track made good) displayed on the HSI the trick after passing the beacon inbound was to choose a heading which resulted in the specified track being displayed on the HSI. I suggested to crews they didn't need to watch the ADF needle too closely - fly the specified track and the approach lights will appear where they should.

Because of the conditions under which it was tested the IR was valid for all types.
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Old 18th Nov 2018, 11:22
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Originally Posted by Big Pistons Forever View Post
The last NDB approach I shot for real in IMC without some sort of GPS track guidance was 1994. The technology is 90 years old and ground stations are disappearing rapidly, I don't understand why this is still being taught.
never said I didn’t have the trusty Garmin Aera 500 moving map as well!
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Old 18th Nov 2018, 12:20
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I still love the old Bendix T12.
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Old 18th Nov 2018, 16:36
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Originally Posted by TangoAlphad View Post
There is a Scottish regional turbo prop operator that flies them daily without GPS overlays.
My question would be why is an airline not using the safest most accurate nav aids for their operation.
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Old 18th Nov 2018, 17:17
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Cannot understand in this day and age why we still use pre WW2 technology.
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Old 18th Nov 2018, 19:39
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I still love the old Bendix T12.
New-fangled rubbish.

We did have the benefit of a moving map as well - Decca roller map, which was fine until the stylus started ripping into the paper map.
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Old 18th Nov 2018, 21:31
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Originally Posted by Big Pistons Forever View Post
The last NDB approach I shot for real in IMC without some sort of GPS track guidance was 1994. The technology is 90 years old and ground stations are disappearing rapidly, I don't understand why this is still being taught.
Big Pistons Forever
My question would be why is an airline not using the safest most accurate nav aids for their operation.
We fly NDB approaches regularly in Russia without GPS overlay, why you ask, well simple their mapping structure is not aligned to the WGS84 which is the basis of GPS therefore if you use your GPS you won't be in the place you are supposed to be.

Beagle
I was once told that old Soviet procedures used 2 NDBs aligned with the instrument RW. With 2 x ADF receivers and a twin needle display, all the pilot had to do was to turn to keep the needles aligned. After passing the 'outer', the indications became even more intuitive - same after passing the 'inner'. Cheap and simple - if the pilot had been properly trained and was in current practice.
Yes nearly every NDB approach in Russia has two NDB beacons, the last beacon on the approach is always at minimums and you will always be tracking towards it therefore greater final approach track accuracy as you approach minimums, plus as the needle swings its time to go-around if nothing seen.

ATC
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Old 19th Nov 2018, 13:27
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Originally Posted by TangoAlphad View Post
The airfields don't want to pay for the new approaches.
Not strictly true. Of the nine airfields in question (excluding Dundee and Inverness), only two - Benbecula and Stornoway - still have only conventional procedures. All the rest have either only RNAV procedures, or both conventional and RNAV.
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