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 |
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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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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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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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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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. |
^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. |
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 ! |
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. |
My advice, ditch the ADF 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? |
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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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 . |
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
(Post 10313289)
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.
Because of the conditions under which it was tested the IR was valid for all types. |
Originally Posted by Big Pistons Forever
(Post 10313950)
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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https://cimg2.ibsrv.net/gimg/pprune....a0dc534df.jpeg I still love the old Bendix T12. |
Originally Posted by TangoAlphad
(Post 10313993)
There is a Scottish regional turbo prop operator that flies them daily without GPS overlays.
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Cannot understand in this day and age why we still use pre WW2 technology.
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I still love the old Bendix T12. 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. |
Originally Posted by Big Pistons Forever
(Post 10313950)
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. 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. ATC |
Originally Posted by TangoAlphad
(Post 10314320)
The airfields don't want to pay for the new approaches.
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