NDB Tracking with wind
 

Can someone please advise me if there are any permited procedures to allow a pilot to adjust the outbound track of an NDB procedure to allow for a very strong crosswind.
Example: the published outbound track 090 with a 50 kt wind from the left.
Thanks

Pack2

I think you may need to revise your basic ADF flying. You should be able to track away from an NDB on a specified ground track, regardless of wind.

2D

"I think you may need to revise your basic ADF flying. You should be able to track away from an NDB on a specified ground track, regardless of wind. "

Hmmm,I don't think that was the question!

Pack 2 asked if there were any adjustments permitted to outbound track as there is in the hold.i.e 3 times drift to allow for a crosswind into the hold.
Legally speaking i'm not sure, but it would make sense to be wide enough so as not to drift through the inbound track on the base turn at rate one.

Anyone more knowledgable care to comment?

I'm not a pilot but would suggest that providing you remain within the Holding Area slight adjustments to track should be OK. If you go outside the HA you may conflict with other traffic.

If a specfic track is shown it should be flown as promulgated since to do otherwise might compromise obstacle clearance.

Within a holding procedure allowance should be made for wind effect also.

For an approach with a base turn you must fly the published magnetic track. Similarly when joining a hold by the off-set (teardrop method) you must fly the 30 degree offset regardless of the wind.
However if the approach involves a procedure turn (rather than a base turn) you should correct for the effects of wind.

The source material for all this is PANS OPS 8168

2 Donkeys
If you were an instrument rated pilot you would know why I asked the question which had nothing to do with the specific track outbound from the NDB rather I was asking what method other people use to prevent overflying the inbound track when you have an excessively, Ie over 50 kt, crosswind outbound.

May I forego the suggested basic trainning review in light of the fact that in this end there is 20,000 hours of flying and over 5,000 hours of IF time

Pack 2

Before you and 2D's get into a pi$$ing contest as to hours flown ( ;) ) I would like to point out that your first post has probably been read by 99% of readers as "can you deviate from the published approach tracks", to which the answer is no if at all possible - if you have such a crosswind you adjust accordingly and try and fly it as close as possible.

In your second post you redefine the question by asking "what methods do people use to prevent overflying tracks". That question is probably better in one of the flying fora rather than the ATC one.

From an ATC point of view we couldn't care less how you achieve the procedural tracks required, just that you achieve them, especially when we're providing separation based on specific tracks being flown.

Yes. PANS-OPS Vol I 3.3.3.6

Wind effect. Due allowance should be made in both heading and timing to compensate for the effects of wind to regain the inbound track as accurately and expeditiously as possible to achieve a stabilized approach.

Pack2 - not sure whether you have your answer, or even if most of us really understand the question? I'm not sure what your 20,000hr are on, but 50kts 'across' (not THAT unusual) on jets equates to around 15 degs of drift to track outbound, and with the (recommended) correction on the procedure turn (?left? - assuming that is what you are trying to fly?) you should not go through the inbound track. If, of course, your time is on 'helos', the drift is a tad more!:D

'Correcting' tracks for wind, as stated above, gives ATC a headache and COULD infringe terrain clearances. Perhaps it will help us and ATC if you tell us where and what have you encountered as a problem?

Either I'm missing something or reading too much into this, not sure which.

You fly whatever heading is required to maintain the published track, you don't correct the track. If you have to fly a heading of 050 to maintain the track of 070 then so be it, as long as you are on the 070 radial what is the problem?

The problem is that the base turn at the end of that 070 outbound assumes nil wind. If there's a substantial wind component blowing across the final approach track, your turn will not end up on the FAT.

Say the inbound is 270, and the wind is 360/40. If you start from the end of the 070 radial outbound, at the end of your 200 degree right turn you'll end up almost a mile south of the FAT, which is not a good place to begin a stabilised approach.

The principle is similar to that of allowing "triple drift" on the outbound leg of a crosswind hold to compensate for the different radii of the turns.

The only way I can see this being a problem is if, when performing the base turn, you move the heading bug immediately 200 degree onto the inbound track and ignore the needles.

Basic IR training was to watch the needle throughout the turn, enabling you to judge your location relative to the inbound track and adjust the turn as necessary. Surely exactly the same airmanship skills should ensure a strong wind isn't a problem. Unless you forget about the wind of course;)

Basic IR training also teaches to be within 5 degrees before descending to the next alt/height. Procedure tracks should be flown as charted - if you happen to overshoot the inbound track you apply an appropriate attack and maintain alt until within 5 degrees and then descend (talking non precision approach here).

Basic IR training was to fly rate 1 turns and not exceed that rate. If you find yourself too wide in the base turn, sure, you can reduce the rate of turn. But if you find yourself too tight, are you suggesting that you should increase your rate of turn?

This appears to directly contradict PANS-OPS. Do you have a regulatory reference for that assertion?

Not suggesting you change your rate of turn, but if you're undershooting you roll out of the turn early to increase the angle at which you are intercepting the inbound track to ensure you intercept before the FAF, if you overshoot then continue the turn through the track to re-intercept.

Again, this is all basic stuff. I think I must be missing the point of the original question.

Yes, I don't think Cosmos is misunderstanding the question at all. Of course you fly the required heading to maintain the outbound (published) track. Having arrived at the end of the o/b leg, and turning at Rate 1, it is not possible to compensate in the turn for a wind that will take you through the Inbound (Final Approach) Track. So when you go through you just have to re-establish from the other side.

I speak from a helicopter perspective where, as someone has said, the drift problem can be quite large. And that's what we do.

I don't think anyone is misunderstanding the question. The issue is over the right answer! Three of you now have given answers that appear to contradict PANS-OPS.

PANS-OPS uses the same words to describe the adjustments permitted on the outbound leg of a course reversal in a procedure as it does for the outbound leg of a hold. But you presumably wouldn't fly the published outbound track of a hold in a strong crosswind, would you?! You'd compensate for drift in the turns by flying "triple drift".

So why not compensate for that on the outbound leg instead? Isn't it better to be a mile north of published track at the end of the outbound leg than a mile south of track when you turn through the inbound heading? I can think of two advantages: obstacle clearance is greater for the initial leg than the final leg; and you aren't messing around trying to re-establish from the other side when you should be flying a stabilised approach.

Is it me....or is this better suited to Tech Log or Qestions Forum....?

The maximum allowable drift to be applied outbound is 30 degrees.

If the drift is more than that then you could alter the bank angles for the turns, or in exceptional cases you could fly a wings level segment in the upwind turn.

If these measures are insufficient for maintaining the inbound track, you could ask ATC to fly inbound on a slightly different track.

Alternatively, don't bid to fly in windy weather.:O

Bookworm - I'm having a little difficulty adjusting my ideas. After 30 plus years of being taught, and then teaching that you don't adjust the o/b track, only the heading to maintain that track - well, the ideas get a bit set! However, you have a point and it would make things much easier if I can convince myself you are right.
I have read PANS-OPS 3.3.3.6 for myself, now and it certainly says you can adjust heading and timing to "regain the inbound track as...expeditiously as possible". If only it would say "adjust track and timing". Still, the aim certainly appears to be to achieve the i/b track as neatly as possible.

Incidentally, I agree this belongs in Tech Log.

keithl

I opened PANS-OPS fully expecting to be able to quote the passage where it said "don't adjust the o/b track", and was just as surprised as you were to find instructions to the contrary. :)

At the risk of repetition, there are two points I'd make in support of my assertion that it should be interpreted as allowing variation of the o/b track, not just o/b heading:

1) almost identical wording to the requirements for the o/b leg of the hold, where it's obvious that track must be adjusted

2) the risk management aspect that, if you must be off track soemwhere, it actually makes more sense to be off the outbound leg than off the final approach.

If we do some sums, the result may appear more palatable.

Consider a 3 minute leg on a nominal 070 radial followed by a right turn to intercept the 270 inbound, flown at 120 kt, and a wind of 360/25. The extra width of turn is close to 1/2 mile (25 knots for 68 secs). To compensate for that, an outbound track of approx 065 is required. Double the crosswind to 50 kt and the track compensation required is still only 060.

So we're not talking "triple drift" here, just a few degrees into wind.

Using expedients like triple drift in a 1-minute holding pattern is rather different to applying it to a 2 or even 3 minute outbound leg of a base turn procedure. For a start, there is a whole lot more protection area around the holding procedure and, as I've already indicated, the timing is vastly different as well.

The splay angle is a function of the outbound time and the TAS. In a nil-wind situation, you would arrive at the FAT very neatly. There is quite a bit of protection for the reversal. Pans Ops allows the designer to use a 2h+47 wind or a "statistical wind" in developing the protection area. If the Pans Ops standard 2h+47 is used then, for example at 5,000 feet, the accounted wind strength would be 2 x5 +47, or 57 knots. I would think that if a statistical wind value was used at a place that experiences a lot of 50+ knot winds, that would be taken into account. And the wind is applied omni-directionally so that we account for it from every direction.

So, putting all of that together, no its not a good idea to modify the outbound track of the initial approach procedure. You would have no idea whether you'd be within the protection area or not, by the time you reached the end of the outbound timing. There is every chance that the strong wind has been taken into account in the protection of the turn. So, while you are certain to fly through the FAT, you simply keep the turn coming around.

Then, as has already been said, once within your regulated tracking tolerance (5 degrees in most places), commence descent while still intercepting the FAT. Then just hope there's enough time to reach the MDA, at or before the MAPt. Slowing the speed a bit in such a situation might help to improve your chances of using the remaining time on final approach.

There is a fair bit more to the design of a non-precision procedure, like ensuring that the rate of descent on final approach does not exceed Pans Ops limits for the nominal timing, but I hope this has helped.

OzExpat - I don't seem to have an earlier post from you in this discussion. Wouldn't want to miss any pearls...

Yes, one of the things bothering me is descending outbound if one isn't within 5deg of the published track. Another thought is that Jepp plates show a fix symbol at the end of the o/b leg of a base turn procedure, which implies that you go to that point and not to some 'adjusted' point.

Having said that, your "statistical wind" certainly doesn't cope with several base turn procedures that I know.

Bookworm - I agree with your points 1) and 2) and yet they're not quite enough to get me off the fence - on which I'm now firmly impaled! It might be possible to compromise by saying "use the 5deg tracking tolerance and track up to 5deg into wind", but that's getting very theoretical. It's all I can do to get guys to keep within 5deg!!

I dunno...

Not sure I follow that. Are you suggesting that there is less protection at the end of the outbound timing than after the completion of the inbound turn?

I really don't see the harm in modifying the outbound track to end up a mile off the nominal track when the protected area is, what, 6 miles? It's not a question of whether to be off track. You're going to be off-track somewhere on the approach, so it's a question of when.

I think you're looking at it with blinkers, OzExpat. At the risk of sounding flippant, as long as the aircaft doesn't hit anything on the approach, you can say you've done your job as procedure designer. But there's more to it than that for the crew: "hope there's enough time to reach the MDA" is not really compatible with the modern view of the stable, constant angle approach planned long in advance. To get that right, the aircraft needs to be intercepting the final approach track as early as possible, not after an S-turn through the FAT.

Finally, I must admit to blinkers too. I'm normally flying a Cat B procedure, often charted with a smaller splay angle than the Cat C/D. That means I'm confident that there is more protection on the outside of the turn. If it's there, I want to use it to reduce the risk of an unstablised approach when inbound.

Why not just fly the Cat C procedure then? If the wind is "helping" me in the turn i.e a northerly wind when I'm turning onto an onbound of 050 I'll do the Cat B, but if it's a strong wind blowing me through the inbound I'll do the Cat C.

Why make up some numbers off the top of your head if there is a published procedure there to help?

What about if it's a conventional NDB procedure turn (hockey stick, like some might call it)....you fly the published track outbound for the appropriate timing and then you turn 45 degrees for 45 sec before turning 180 to intercept the FAT. Surely you cannot modify the outbound track that is published, but can you modify the heading/timing of the reversal to account for winds?

Bobrun - I don't think there's any problem with a Procedure Turn reversal. What we're trying to thrash out is the Base Turn reversal, outbound track.

Although, fair enough, the original question didn't actually specify for a Base Turn procedure, nonetheless that's the only kind that gives a problem in a strong crosswind.

All my NDB procedure turns were the hockey stick style and the 45 degree turn was in addition to the wind correction to properly track outbound. Extra time was added to the barb when necessary to avoid being blown past the FAT. None of this is different from VOR, ILS etc. when flying a procedure turn.

I tried to work the outbound and turn back to have several seconds on an intercept angle, especially with an NDB. With an NDB, it really helps to have some time on the inbound to nail the corrected heading before station crossing when the back bearing needs time to settle down. One instructor's recommendation was to stick to that heading for half the approach time and then make a double drift correction and stick to that until MAP.

When you have a track 20 degrees off the FAT, you very much want to remain on said track and within the outbound distance, whichever way the wind is blowing. Tracking away from an NDB is usually not as accurate as tracking to; so, any other available guidance may be useful, especially if terrain is a factor.

Yep, when the wind is blowing you back to the FAT, the turn back will ultimately need about twice the drift correction added to the basic turn and a rate 1 turn might not be fast enough.

Before flying any NDB procedure, you really want to make very sure that your compass is properly swung:uhoh:

Hi keithl
It was at the very start of the first para of my previous post. :ok:


In THAT event, Pans Ops says that you MUST be established on the outbound leg by the time you reach that point. I thought that the discussion related to an NDB-only procedure tho.


Then you probably need to take the matter up with the Regulator of the State concerned.


Hi bookworm
No, I'm saying that there is less protection for that WHOLE manoeuvre than there is in any part of the protection area for a holding pattern.


You're making an assumption here that I would regard as dangerous. My main problem with this is... okay, so you fly a 5-degree offset as indicated on your ADF. How do you KNOW FOR SURE that your ADF needle is properly calibrated? If you actively insist on going at least 5 degrees OFF the published track, you have just eroded ALLLLLLL of your regulatory tracking tolerances. Is your ADF needle really sensitive enough for that? I would counsel some caution on that, if you're flying raw data.


No blinkers at all. I've been flying NDB approaches my whole flying career. This is the fact of any single navaid approach because you really have no clear idea of exactly where you are, with reference to the NDB (on a single navaid approach). All that I can do as a procedure designer is abide by Pans Ops. Sure, I could add another half minute, or full minute, outbound to the timing (well, maybe I could!) but then I'd get complaints about an excessively long procedure. I can't win, so I just go with Pans Ops and add nothing to timing - unless there are constraints for ROD on final, of course. And that IAW Pans Ops too.


Yes and no. If you're flying at Cat "C" speed the whole way, then you should be safe because the higher TAS means less time for wind effect. At Cat B speed, you're flying slower than Cat C and, therefore, are under wind (drift) influence through the turn for longer. This gets a bit hypothetical because of turn rate, of course, but the basic situation means that there's a chance that you may not be fully protected for the base turn because you have a lot more degrees to turn through at the lower speed - and that is not taken into account in the design of the procedure (ie using the Cat C outbound track in a Cat B aircraft at Cat B speeds).


I have to assume here that you're talking about flying a single navaid approach in a large-ish heavy jet? I'm not sure that any such aircraft are well equipped for such a procedure these days because it is very difficult to meet the criteria for a stabilised approach in those circumstances.

Pack2

Unless I misunderstand you, this is my Eurocents-worth:

Apply 1x Single Drift and adjust outbound time by the calculated tailwind component x Y, where Y is the nominal time of the procedure. As the SD is a function of the aircraft's TAS your info was incomplete to allow analysis.

The time adjustment should prevent you from being blown significantly through the inbound axis. To avoid excessive track distortions do not use a Drift correction of >30 degr.

When someone has been cleared outbound for the procedure (either with or without descent) you are the only aircraft in the procedure until you cross the beacon inbound. This in order to provide aforementioned minimum procedural separation.

Hi, OzEx

Yes, we are discussing the plain NDB approach, but what I was trying to say was: If an NDB/DME has a fix at the end of the o/b leg, then (a) that limits even further one's freedom to adjust for(anticipate) the drift in the turn, and (b) shouldn't the outbound time also be regarded as a kind of DME, in the sense that clearances are calculated on the basis that the time takes the a/c to a certain position along the o/b radial?

4Reds - I'm more concerned with separation from obstacles than from other aircraft.

I fear I'm not making my point well, for lack of a diagram. If, instead of adjusting the o/b track, I fly the published outbound and accept that the turn will roll out past the final approach track, then at the moment of roll out I will also be 5 degrees off the final approach track. Isn't that equally "ALLLLLLL of my regulatory tracking tolerances"? Why is that in some way better than being off track on the o/b leg?

One advantage that I have in making the correction on the o/b is that I have course guidance and, within the accuracy of the instrument, I know where I am with respect to the published track. I can make sure that I'm no more than 5 degrees off. By contrast, if I fly the published o/b and accept the drift in the turn, the first I'll know about how far off the FAT I am is when I see the needle indicate it at the completion of the turn. For all I know, it may be 10 degrees off.

Having said that, your "statistical wind" certainly doesn't cope with several base turn procedures that I know

The use of the omni directional wind or the stastical wind as far as I am aware is not to make it easy to join the inbound easily in a large crosswind as described. I believe that the wind is used to calculate the shape and size of the protected area that one could drift into should one pass through the final approach track.

The outbound track must be tracked as accurately as possible.

This whole argument about tracking outbound in a severe crosswind is the exact same as doing say an NDB/DME base turn when there is say a 50Kt tailwind on final approach........would anyone seriously considder exceeding the outbound DME to provide suficient time to descend on final approach to circling minima?

Regards,

DFC

keithl... A fix is normally used at the end of the outbound leg to reduce the dimensions of the protection area. Thus it is a mandatory turn point. Timing is not quite so simple because there is no real guarantee as to how far away from the NDB you are at the end of the time period. This is obviously a function of how the wind affects your progress - a tailwind will take you further away, while a headwind will mean you are much closer to the NDB.

Thus it is necessary to adjust the timing, in order to compensate for the effect of a known wind. The whole idea of this is to ensure that you will be far enough away that the reversal maneouvre gives you a fair chance of intercepting the FAT. The first paragraph of DFC's post has said the same thing that I've been trying to say.

Indeed, FOUR REDS is correct about the application of drift. I've had to contend with some pretty significant drift on a NDB procedure and have only ever applied enough correction to adjust for that and, therefore, remain on course within the legal tracking tolerances. As I commence the reversal, I slow down a bit more than usual so that I won't overshoot the FAT too much. It soon becomes apparent if I'm going to overshoot it, so I simply keep the turn coming around, to re-intercept the FAT because that is what I must do - and I know that the procedure will protect me while doing so.

This might also satisfy bookworm's concern about being outside the legal tracking tolerance after overshooting the FAT. Sure, you might be 5-degrees of the FAT, but you are continuing to turn, to re-establish that track. The sooner that you can establish yourself within 5 degrees of the track, the sooner you can start descent in the final segment. It's not perfect, of course, but there isn't a lot more that a designer can build into this type of approach.


This is at the expense of exploring the outer limits of the outbound protection area on the up-wind side. There is comparitively less protection here because Pans Ops assumes that the pilot will track outbound as accurately as possible. There is basically more protection for the reversal because of the vagaries of wind, the different TAS and bank angles of different aircraft, etc. All of this implies that there is less accuracy in this maneouvre and hence the protection area makes a lot of worst-case assumptions to provide protection.


I'd venture to suggest that you will have a pretty reliable indication of this situation when you're halfway through the reversal turn. I certainly watch the needle movement through the turn, to get the earliest possible indication of overshoot, or even undershoot. For an overshoot, I then have the flexibility of going to 30-40 degrees of bank quite safely at this stage, to minimise the amount of overshoot. I know that some companies limit bank angle to 25 degrees, but I am not so limited.

I guess it has to be said that, if you're getting significant cross-wind on the o/b leg and then not have enough time to reach MDA after re-intercepting the FAT, a go-around will be necessary. Indeed, if the cross-wind is truly significant (I would classify 50+ knots that way), there's a pretty good chance that the cross-wind on the landing runway could be very close to the maximum for the aircraft anyway. In that event, I'd be looking for an alternate aerodrome or, at least, an alternate procedure to another runway.

I wonder if we're starting to get too technical in responding to the initial enquiry? :D

If you're prepared to break the model of maximum 3 deg/s turns, then I think the problem is significantly mitigated. At 150 kt a 3 deg/s 180 deg turn has a diameter of 1.6 miles. Thus at 5 deg/s a 180 deg turn has a diameter of about a mile, and gives you 0.6 mile lateral correction that can be applied within the turn. If my trig is right, that's 34 degrees bank angle for 5 deg/s if 22 degrees gives you the 3 deg/s, which doesn't seem unreasonable.

For the pedantic like me, is that permitted by PANS-OPS? It says that procedures are based on 3 deg/s (25 deg max bank) and that holding turns are to be made at that rate. It doesn't mandate that rate for reversal turns.

Perhaps for those of us without Ops Manual limitations, tightening the turn is the pragmatic answer. But I'm not looking forward to explaining that to my examiner...

A good analogy, DFC, but I think the problems are less pronounced along-track than across-track. Most teardrops (in the UK at least) seem to provide for completion of the reversal at least a mile before the FAF. Thus, although things happen more quickly with a tailwind, there shouldn't be a problem with being in a position to descend with the procedure at the FAF.

By contrast, someone performing an NDB approach to an on-airfield beacon who rolls out of the turn a mile off the FAT and, say, at 6 DME with a 5 DME FAF, is 10 degrees off the FAT, and needs to take a 25 degree upwind cut to get to 5 degrees by the FAF. Add to that the probably 15+ degrees of drift and it starts to conform to my vision of "pear-shaped" ;) For an ILS approach where a LOC is involved, it's worse because half-scale deflection is much closer to the FAT.

Pack2's question was about "permitted procedures". I think it's within scope to discuss the wording of PANS-OPS, its interpretation, the consequences of different interpretation for risk management and pragmatic solutions. (But then again this is PPrune, so when has the scope of the original question ever mattered a jot... ;))

Pans Ops merely uses a set of assumptions so that a protection area can be constructed. One of these assumptions is that all pilots can execute a turn in IMC at 25 degrees of bank. If you are free to use a (slightly) steeper bank angle, you can be assured of remaining well within the procedure's primary protection area.

When it comes to explaining it to the examiner, your only limitation will be any limit recorded in your SOPs, or related to your particular aircraft. Besides, if one can use a slightly steeper bank angle, there's a better chance of staying on the up-wind side of the FAT, making for an easier intercept with maximum protection afforded by the procedure.


Sure, it won't look pretty but, provided that you keep turning to intercept the FAT, you'll be protected by the procedure. This would seem to reinforce the need to monitor the turn on the ADF needle, as I mentioned before, and tighten the turn a tad, if necessary (and if the option to do so is available to you).

Bear in mind too that, inherent in the Pans Ops assumption of a 25 degrees bank angle, they refer to it as average achieved bank angle. I see nothing wrong with using 30 degrees of bank initially as it will help to account for the time the aeroplane takes to achieve the magic minimum bank angle.


Thanks for the confirmation - just thought that I should check! :D

Haven't heard much from Pack2, have we?!

OK, I'm persuaded that there's less protection around the o/b leg than around the base turn. So I'll come off the fence and revert to my original practice of tracking the o/b leg as accurately as possible.

But bookworm's quote of P-OPS 3.3.3.6 must then be admitted to be misleading? untrue? ambiguous? which do you prefer?

No keithl, there's no "either-or" situation here. By all means, set a heading to compensate for the drift and, thereby, stay on track as closely as possible. Given the original situation which, at least in my mind, specified a 50 knot cross-wind on the outbound leg, then your heading correction will give you a headwind component. Now you need to make a (slight) timing adjustment to account for the slightly reduced groundspeed.

The whole aim of the exercise is to get the aeroplane far enough away from the beacon that the reversal manoeuvre works out fairly closely. To close in and you'll never reach the FAT in time to make any reasonable descent.

Has this helped?

For the record, here are the words from PANS-OPS Vol I Part IV, Holding Procedures

1.2.3 All procedures depict tracks and pilot should
attempt to maintain the track by making allowance for
known wind by applying corrections both to heading and
timing during entry and while flying in the holding pattern.

1.4.2 Corrections for wind effect. Due allowance
should be made in both heading and timing to compensate
for the effects of wind to ensure the inbound track is
regained before passing the holding fix inbound. In making
these corrections full use should be made of the indications
available from the aid and estimated or known wind.

Apparently, it's OK to adjust "heading and timing" to skew the outbound track of a hold, as we all do, but not to adjust "heading and timing" to skew the outbound track of a course reversal, despite the same words... ;)

(I'm very happy to leave it at that. If this thread has got people thinking about the issues, and allowed some excellent points to be made by all contributors, then it has done its job.)