Instrument approaches: the outbound leg
Why do it if it's not fun?
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Instrument approaches: the outbound leg
A question which came up at work recently, and which we couldn't agree on an answer to:
Have a look at the plate for the ILS/DME RWY 28 approach at Blackpool (AIS website registration required to access to the link), although the question could probably apply to any ILS approach with a procedure turn (rather than a base turn) in it.
In this approach, you reach the beacon (which is on the airfield), and possibly enter the hold, before leaving the beacon on a track of 099 - the reciprical of the ILS inbound track, which is 279. You then fly a 45/180 procedure turn to establish on the localiser.
What should you be tracking whilst flying this outbound leg? Do you track 099 from the NDB? Or do you track the localiser in the reverse direction?
Myself and a colleague disagreed on this one. I explained my point of view, he explained his, and we decided that we both had valid points and neither of us knew which was correct. So my colleague e-mailed Steve Oddy (CAA staff examiner, and author of RANT), who very kindly replied extremely promptly. I'll post later and let you know what his reply was, but I'm curious what the concensus of the forum is first.....
FFF
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Have a look at the plate for the ILS/DME RWY 28 approach at Blackpool (AIS website registration required to access to the link), although the question could probably apply to any ILS approach with a procedure turn (rather than a base turn) in it.
In this approach, you reach the beacon (which is on the airfield), and possibly enter the hold, before leaving the beacon on a track of 099 - the reciprical of the ILS inbound track, which is 279. You then fly a 45/180 procedure turn to establish on the localiser.
What should you be tracking whilst flying this outbound leg? Do you track 099 from the NDB? Or do you track the localiser in the reverse direction?
Myself and a colleague disagreed on this one. I explained my point of view, he explained his, and we decided that we both had valid points and neither of us knew which was correct. So my colleague e-mailed Steve Oddy (CAA staff examiner, and author of RANT), who very kindly replied extremely promptly. I'll post later and let you know what his reply was, but I'm curious what the concensus of the forum is first.....
FFF
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I think you should be tracking BPL(NDB) outbound as that is the IAF. I've not thought about this before, but tracking an ILS outbound would require backcourse equipment otherwise the ILS does not operate as a command instrument. That and 2deg sensitivity.
I reckon you're tracking outbound from the IAF which is based upon the BPL; therefore, track 099 deg.
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Black art ? I don't think so !
I think that you are making this all far too complicated.
First what dose it say on the top of the plate ? ILS DME rwy 28 so the approach is NOT based on any NDB but you must have a minimum of LOC & DME to fly the approach if you have GS so much the better.
The only function of the NDB is for the hold and to get you overhead the field to start the ILS/DME approach if you can find your way to overhead the field some other way (radar or area nav) then you dont need to use an ADF.
I think it is time for some common sence to be applied the LOC back course takes a lot less cockpit workload to track than an NDB and is far more accurate so why make life hard for yourself, keep the cockpit workload down to a minimum level and use your brain power for the important stuff.
I am fully aware that some might want to turn this into a black art but it's just flying !
KiltieYou are quite correct that LOC backcourse approaches are not approved in the UK but this is an ILS/DME and the critical part of the approach is not being flown as a backcourse.
It is common sence to fly the aircraft in the most accurate way and using the LOC to position outbound is doing just that if the approach required the use of an NDB the it would say NDB ILS DME rwy 28 at the top of the plate!!
First what dose it say on the top of the plate ? ILS DME rwy 28 so the approach is NOT based on any NDB but you must have a minimum of LOC & DME to fly the approach if you have GS so much the better.
The only function of the NDB is for the hold and to get you overhead the field to start the ILS/DME approach if you can find your way to overhead the field some other way (radar or area nav) then you dont need to use an ADF.
I think it is time for some common sence to be applied the LOC back course takes a lot less cockpit workload to track than an NDB and is far more accurate so why make life hard for yourself, keep the cockpit workload down to a minimum level and use your brain power for the important stuff.
I am fully aware that some might want to turn this into a black art but it's just flying !
KiltieYou are quite correct that LOC backcourse approaches are not approved in the UK but this is an ILS/DME and the critical part of the approach is not being flown as a backcourse.
It is common sence to fly the aircraft in the most accurate way and using the LOC to position outbound is doing just that if the approach required the use of an NDB the it would say NDB ILS DME rwy 28 at the top of the plate!!
Last edited by A and C; 14th Feb 2006 at 11:54.
Keep the workload down? I don't think that flying effectively a backcourse outbound and then normal sensing inbound is reducing the workload. You should have the NDB tuned anyway for IAF so all you have to do is track outbound. It's not that the back cse is inherently difficult but at times of high workload, fatigue, wx etc it has often reverse sensing can be confusing.
Also, it may be an ILS/D approach but the MSA are based upon BPL sectors and the IAF (BPL again) is part of the instrument approach so you cannot execute the approach without it.
Also, it may be an ILS/D approach but the MSA are based upon BPL sectors and the IAF (BPL again) is part of the instrument approach so you cannot execute the approach without it.
Why do it if it's not fun?
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So far, 3 replies in favour of the NDB and 1 in favour of the localiser.
One interesting point regarding the localiser, though: if you choose to use this, you are not using the back-course. The back-course would be on the approach to the other runway, runway 10. What you are doing is using the front of the localiser, but backwards.
Back-course approaches are a completely different subject. (And - HWD - they don't require any special equipement, just a knowledge of how to interpret the instruments.)
FFF
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One interesting point regarding the localiser, though: if you choose to use this, you are not using the back-course. The back-course would be on the approach to the other runway, runway 10. What you are doing is using the front of the localiser, but backwards.
Back-course approaches are a completely different subject. (And - HWD - they don't require any special equipement, just a knowledge of how to interpret the instruments.)
FFF
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A and C,
I'm not sure I agree that the NDB complicates matters in this case. In my simple mind the easiest approach I think would be to have the HSI/VOR already on on the ILS track and the HSI/DG bugged for intercept and follow the RMI/RBI. In other words have two instruments for different parts for the approach and setup accordingly.
FFF,
Indeed, I don't think I contradicted that. The point I am making is simply that unless you have a backcourse button the thing that looks like VOR/HSI no longer operates like one. Surely a case of Murphy's law if ever there was one 
I'm not sure I agree that the NDB complicates matters in this case. In my simple mind the easiest approach I think would be to have the HSI/VOR already on on the ILS track and the HSI/DG bugged for intercept and follow the RMI/RBI. In other words have two instruments for different parts for the approach and setup accordingly.
FFF,
HWD - they don't require any special equipement, just a knowledge of how to interpret the instruments.
Last edited by High Wing Drifter; 14th Feb 2006 at 11:30.
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First to correct some misconceptions;
Balckpool only has an ILS on 28. The signals transmitted along the approach to 28 are what is knows as the "front course" regardless of which dirction the aircraft is travelling. If one travels along the approach to 10, the ILS LOC signal received will be what is known as the "back course". It is in this area that the signals are not to be used.
To answer the question;
Annex 10 Volume 1 is the reference.
The upper boundary of the useable localiser signal is defined as a surface with a slope of 7deg from the horizontal starting at the localiser antenna.
Thus an aircraft at 3000ft will have to be about 4nm from the antenna to enter the useable signal area. At 2000ft this reduces to about 2.7nm (if my trig is correct!).
Add to the situation the fact that while the NDB is on the field in this case, it is not on the runway centerline and the allowed position of the aircraft with respect to the NDB when in the overhead.
So the answer is that the NDB must be used to track outbound until the aircraft is within the localiser coverage (between 3.7 and 5 dme outbound (the runway is about 1nm long!) depending on height) when the localiser could be used. But of course, things like DME slant range has to be taken into account when close in at such heights!
From the parctical point of view - track the NDB with an eye on the LOC as the procedure turn is reached to ensure that the procedure turn is started from a position as close to as possible the ideal correct fix.
I know the LOC would provide more accurate tracking (when used correctly) but the procedure designer has allowed for the errors in the NDB system.
Regards,
DFC
Balckpool only has an ILS on 28. The signals transmitted along the approach to 28 are what is knows as the "front course" regardless of which dirction the aircraft is travelling. If one travels along the approach to 10, the ILS LOC signal received will be what is known as the "back course". It is in this area that the signals are not to be used.
To answer the question;
Annex 10 Volume 1 is the reference.
The upper boundary of the useable localiser signal is defined as a surface with a slope of 7deg from the horizontal starting at the localiser antenna.
Thus an aircraft at 3000ft will have to be about 4nm from the antenna to enter the useable signal area. At 2000ft this reduces to about 2.7nm (if my trig is correct!).
Add to the situation the fact that while the NDB is on the field in this case, it is not on the runway centerline and the allowed position of the aircraft with respect to the NDB when in the overhead.
So the answer is that the NDB must be used to track outbound until the aircraft is within the localiser coverage (between 3.7 and 5 dme outbound (the runway is about 1nm long!) depending on height) when the localiser could be used. But of course, things like DME slant range has to be taken into account when close in at such heights!
From the parctical point of view - track the NDB with an eye on the LOC as the procedure turn is reached to ensure that the procedure turn is started from a position as close to as possible the ideal correct fix.
I know the LOC would provide more accurate tracking (when used correctly) but the procedure designer has allowed for the errors in the NDB system.
Regards,
DFC
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Ham Phisted
The first issue that you raise is workload...... well that depends on the equipment fitted in the aircraft I see no increase in workload with a HSI, with an OBI it is different and I can see the increase in workload over a HSI but it would still be less than back tracking an NDB and more importantly far more accurate.
You are correct that the MSA is based on the NDB but as I said if you can locate the NDB position some other way such as area nav then staying within the MSA in not an issue ( the approach radar could also help you with this).
The GA would undoubtedly be harder to fly without the NDB but the area nav would also work for this if you read the plate is says climb straight ahead to 2000ft then left to the locator if a course was required it would say climb on 279 from lctr.
You are correct that the MSA is based on the NDB but as I said if you can locate the NDB position some other way such as area nav then staying within the MSA in not an issue ( the approach radar could also help you with this).
The GA would undoubtedly be harder to fly without the NDB but the area nav would also work for this if you read the plate is says climb straight ahead to 2000ft then left to the locator if a course was required it would say climb on 279 from lctr.
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Balckpool only has an ILS on 28. The signals transmitted along the approach to 28 are what is knows as the "front course" regardless of which dirction the aircraft is travelling. If one travels along the approach to 10, the ILS LOC signal received will be what is known as the "back course". It is in this area that the signals are not to be used.
The sense would be correct for the localilser regardless of what radial was selected, unlike a VOR.
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HWD,
Sorry to keep picking up on your posts - nothing personal!
First of all, you seem to think that a "back course button" would make things easier on a back course. I quote you: "The point I am making is simply that unless you have a backcourse button the thing that looks like VOR/HSI no longer operates like one".
My understanding (having never flown a back-course) is that there is no back-course button which affects the information which is displayed to the pilot. If the aircraft is equipped with an HSI, it will read in the correct sense when flying a back-course regardless. If it is equipped with an OBI, it will read in the reverse sense regardless, and you will need to fly in the oposite direction to what the needle indicates.
However, many autopilots do have a "back course" button. This does not alter the display which the pilot sees - it only determines how the autopilot interprets the ILS data.
None of this is at all relevant to the question I asked, though, because the entire procedure is flown on the front course, which you did recognise in your last post.
But again, you're understanding of what the instruments would show is wrong. You say: "The sense would be correct for the localilser regardless of what radial was selected".
In fact, if you have an OBI, the sense will be incorrect regardless of what radial is selected. The reason for this is nothing to do with whether you are on the front-course or the back-course of the localiser. It is because your heading is approx 180 degrees out from the localiser's final approach course that the OBI will read the wrong way. An HSI would read the correct way.
If you don't believe me, go and draw some diagrams showing the aircraft off-track, and work it out from first principles. Or, even better, go and fly it!
DFC,
The second part of your post is exactly the answer I was looking for, giving a reference (which I will check out when I get a chance), an answer, and a reason. It does, however, make Steve Oddy's reply to the question seem very interesting..... but I'll let the debate go on for a little longer first!
FFF
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Sorry to keep picking up on your posts - nothing personal!
First of all, you seem to think that a "back course button" would make things easier on a back course. I quote you: "The point I am making is simply that unless you have a backcourse button the thing that looks like VOR/HSI no longer operates like one".
My understanding (having never flown a back-course) is that there is no back-course button which affects the information which is displayed to the pilot. If the aircraft is equipped with an HSI, it will read in the correct sense when flying a back-course regardless. If it is equipped with an OBI, it will read in the reverse sense regardless, and you will need to fly in the oposite direction to what the needle indicates.
However, many autopilots do have a "back course" button. This does not alter the display which the pilot sees - it only determines how the autopilot interprets the ILS data.
None of this is at all relevant to the question I asked, though, because the entire procedure is flown on the front course, which you did recognise in your last post.
But again, you're understanding of what the instruments would show is wrong. You say: "The sense would be correct for the localilser regardless of what radial was selected".
In fact, if you have an OBI, the sense will be incorrect regardless of what radial is selected. The reason for this is nothing to do with whether you are on the front-course or the back-course of the localiser. It is because your heading is approx 180 degrees out from the localiser's final approach course that the OBI will read the wrong way. An HSI would read the correct way.
If you don't believe me, go and draw some diagrams showing the aircraft off-track, and work it out from first principles. Or, even better, go and fly it!
DFC,
The second part of your post is exactly the answer I was looking for, giving a reference (which I will check out when I get a chance), an answer, and a reason. It does, however, make Steve Oddy's reply to the question seem very interesting..... but I'll let the debate go on for a little longer first!
FFF
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FFF,
I know that we have established that this has nothing to do with the debate but you did decide to pick up on it, so here I go
I don't really know for real. I was a remark born from the teachings of BGS ground school, that the indications for a backcourse are corrected when backcourse is selected. Obviously the real world is a little different to BGS. Therefore, I stand corrected.
Some confusion here due to my undetailed response. I did mean the sense relative to the ILS track and that it doesn't change by changing the selected radial so things can be a little confusing if you treat it like a VOR. Point taken aboout the HSI. Roll on my IR!
I know that we have established that this has nothing to do with the debate but you did decide to pick up on it, so here I go
However, many autopilots do have a "back course" button. This does not alter the display which the pilot sees - it only determines how the autopilot interprets the ILS data.
In fact, if you have an OBI, the sense will be incorrect regardless of what radial is selected. The reason for this is nothing to do with whether you are on the front-course or the back-course of the localiser. It is because your heading is approx 180 degrees out from the localiser's final approach course that the OBI will read the wrong way. An HSI would read the correct way.
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Forgive me for sounding dumb but isn't it impossible to track out on an NDB? Surely all you will get is a 180 fix as long as you are facing away from it whatever your bearing from the NDB!
Don't you just get overhead the beacon at the correct height then head out on the outgoing bearing specified on the plate (allowing for wind) then rate 1 turn to get 'established' at the correct distance and at the correct height.
I must be missing something.
Don't you just get overhead the beacon at the correct height then head out on the outgoing bearing specified on the plate (allowing for wind) then rate 1 turn to get 'established' at the correct distance and at the correct height.
I must be missing something.
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Track outbound from the NDB.
Funnily enough I only know this cos it is what I did on my initial IR test and I passed!
Funfly. You fly out on the specified bearing relative to the NDB, on a heading which allows for the wind, to ensure the correct track.
Funnily enough I only know this cos it is what I did on my initial IR test and I passed!
Funfly. You fly out on the specified bearing relative to the NDB, on a heading which allows for the wind, to ensure the correct track.
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Originally Posted by funfly
Forgive me for sounding dumb but isn't it impossible to track out on an NDB? Surely all you will get is a 180 fix as long as you are facing away from it whatever your bearing from the NDB!
Don't you just get overhead the beacon at the correct height then head out on the outgoing bearing specified on the plate (allowing for wind) then rate 1 turn to get 'established' at the correct distance and at the correct height.
I must be missing something.
Don't you just get overhead the beacon at the correct height then head out on the outgoing bearing specified on the plate (allowing for wind) then rate 1 turn to get 'established' at the correct distance and at the correct height.
I must be missing something.
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ILS DME rwy 28 so the approach is NOT based on any NDB but you must have a minimum of LOC & DME to fly the approach if you have GS so much the better.
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There's a lot of confusion here!
Yes, you can track outbound from an NDB and know where you are (within the margin of error of an ADF). If you're tracking 090 degrees, and the ADF needle is pointing directly behind you and stays there, you are on a bearing of 090 from the NDB. If the ADF needle is pointing 10 degrees to the left of directly behind, you're on a bearing of 100 degrees from the NDB.
Yes, there are Back-Course procedures in the USA: the VOR display even has a little light labelled "BC" that lights up when you're on one. I had to do one for my FAA IR checkride.
Yes, you can track outbound from an NDB and know where you are (within the margin of error of an ADF). If you're tracking 090 degrees, and the ADF needle is pointing directly behind you and stays there, you are on a bearing of 090 from the NDB. If the ADF needle is pointing 10 degrees to the left of directly behind, you're on a bearing of 100 degrees from the NDB.
Yes, there are Back-Course procedures in the USA: the VOR display even has a little light labelled "BC" that lights up when you're on one. I had to do one for my FAA IR checkride.
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Errrrmmmm surely it is DR, or am I missing something? As far as I can see it doesn't use the NDB, as then surely it would be an ILS/NDB/DME procedure which is not how it is described. Use of back course of LOC is not approved in the UK, so cannot be part of the procedure. So the approved procedure is to DR outbound, and if the procedure turn doesn't give you enough space to correct any errors onto the localiser and get established you'd have to bin the approach. Since a 10° error at 6 nm is only 1 nm error, this should not be too much of a problem!
You can of course use any navigation that you are competent to use, I would suggest the 277° radial of the POL VOR (setting 097° of course!) would be best assuming you have a second NAV box. Surprised it has not come up as a favourite, as it is far the easiest!
So that is what the "BC" button means on my autopilot!
You can of course use any navigation that you are competent to use, I would suggest the 277° radial of the POL VOR (setting 097° of course!) would be best assuming you have a second NAV box. Surprised it has not come up as a favourite, as it is far the easiest!
So that is what the "BC" button means on my autopilot!
So how good is your ADF antenna setup for back bearings?
Agreed I'd track to the NDB and turn OB to 099 -+ wind correction and hold that course for a bit.
My suspicion is that the loc signal will give good data before the ADF will on a back bearing on many SE a/c.
I've done a bunch of VFR back bearing tracks in various SEs and have yet to find one I would trust on an NDB approach
My suspicion is that the loc signal will give good data before the ADF will on a back bearing on many SE a/c.
I've done a bunch of VFR back bearing tracks in various SEs and have yet to find one I would trust on an NDB approach