Instrument Rating Drift Allowances???
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Instrument Rating Drift Allowances???
I am studying for my IREX and I was just wondering if there were any rules not laid down in the books that would allow for wind in the holding pattern.
I asked some of the new IR graduates and they didn’t seem to know of any, however one of the older instructors mentioned 3 times the drift for a 1 min pattern and he thought it was 2 times the drift for a 2 min pattern. He also said there was a rule for the 80degree procedure turn whereby you held that heading for so many seconds but he could not recall how long.
Are there any from the old school who know of these rules?
I asked some of the new IR graduates and they didn’t seem to know of any, however one of the older instructors mentioned 3 times the drift for a 1 min pattern and he thought it was 2 times the drift for a 2 min pattern. He also said there was a rule for the 80degree procedure turn whereby you held that heading for so many seconds but he could not recall how long.
Are there any from the old school who know of these rules?
There's lots. But whatever you do just make sure you have at least ONE technique! There's nothing worse than watching a poor old candidate who has no idea on wind allowance and makes a botch of it.... 
I personally use 2 times the drift outbound in the holding pattern, and 1sec per knot per minute for approach in a headwind, 1/2 second for tailwinds. Works reasonably well.
Make sure you pic something that you UNDERSTAND and even more importantly can APPLY it!
I personally use 2 times the drift outbound in the holding pattern, and 1sec per knot per minute for approach in a headwind, 1/2 second for tailwinds. Works reasonably well.
Make sure you pic something that you UNDERSTAND and even more importantly can APPLY it!
Bottums Up
novicef
From Jeppesen/Terminal/AU-20/3.9.2
As for drift in a holding pattern, I can count on the fingers of one hand the number of times I've had to hold for real. Finding that I rarely knew the actual wind to apply a rule of thumb I'd apply what seemed reasonable, and when turning inbound assess how the outbound drift went.
Whilst inbound, given one is tracking a bearing or preferably a radial, the drift is easy to determine, and then apply on subsequent patterns.
I found that this frees brain space for other considerations.
He also said there was a rule for the 80degree procedure turn whereby you held that heading for so many seconds but he could not recall how long.
a. Procedure Turn (45°/180°) Consisting of a specified track & timing from the facility or fix, a 45° turn away from the outbound track for 1 minute from the start of the turn for categories A and B aircraft (1 minute 15 seconds for categories C, D and E aircraft), ....
Whilst inbound, given one is tracking a bearing or preferably a radial, the drift is easy to determine, and then apply on subsequent patterns.
I found that this frees brain space for other considerations.
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Novicef,
As a general rule, yes you are correct. If you can understand the theory behind it, it makes it simpler to understand.
If you are in a 1 minute holding pattern, holding ten degrees of drift on the inbound leg, after your turn outbound you will require 30 degrees of drift. Basically, the pattern can be dived into four separate parts - the inbound leg, the 1st tun outbound, the outbound leg, and the inbound turn. In a G/A type of aircraft, the inbound leg takes 1 min, oubound turn 1 min, outbound leg 1 min, and inbound turn 1min. Total time of 4 minutes for a 1minute holding pattern. If you are only able to make an adjustment for wind during the inbound and the outbound legs, compensation must be made for the wind effect during the turns. Thus, if you are established inbound and can estimate your drift as being say 10 degrees, you have worked out how much drift is required for 1/4 of the pattern. Now we realise that we must compensate for the outbound leg as well as the turns - equal in time. To find the allowance for the outbound, we now multiply the drift on the inbound leg by 3, as the adjustment is now for the remaining 3 minutes of the pattern. 30 degrees allownace outbound.
Jees this would be easier with a whiteboard!
2 minute pattern, 4 different parts. Inbound 2mins, turn 1min, outbound 2mins, turn 1 min. Total time 6 minutes. 10 degrees drift inbound, 1/3rd of total pattern. Therefore 2/3rd's remaining, multiply by 2 - 20 degrees outbound.
As a general rule, yes you are correct. If you can understand the theory behind it, it makes it simpler to understand.
If you are in a 1 minute holding pattern, holding ten degrees of drift on the inbound leg, after your turn outbound you will require 30 degrees of drift. Basically, the pattern can be dived into four separate parts - the inbound leg, the 1st tun outbound, the outbound leg, and the inbound turn. In a G/A type of aircraft, the inbound leg takes 1 min, oubound turn 1 min, outbound leg 1 min, and inbound turn 1min. Total time of 4 minutes for a 1minute holding pattern. If you are only able to make an adjustment for wind during the inbound and the outbound legs, compensation must be made for the wind effect during the turns. Thus, if you are established inbound and can estimate your drift as being say 10 degrees, you have worked out how much drift is required for 1/4 of the pattern. Now we realise that we must compensate for the outbound leg as well as the turns - equal in time. To find the allowance for the outbound, we now multiply the drift on the inbound leg by 3, as the adjustment is now for the remaining 3 minutes of the pattern. 30 degrees allownace outbound.
Jees this would be easier with a whiteboard!
2 minute pattern, 4 different parts. Inbound 2mins, turn 1min, outbound 2mins, turn 1 min. Total time 6 minutes. 10 degrees drift inbound, 1/3rd of total pattern. Therefore 2/3rd's remaining, multiply by 2 - 20 degrees outbound.
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You will get many differing ideas on this, and generally airline folk will give you a different answer to GA folk (mainly due to the different speeds involved).
For lots of fun stuff that might help you with this, have a look at http://www.flightinfo.com/rulesofthumb.asp
Excellent site.
For lots of fun stuff that might help you with this, have a look at http://www.flightinfo.com/rulesofthumb.asp
Excellent site.
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Macrohard/ Drift for 80 Degree Procedure turn.
Macrohard,
Thanks for that, just one more question. Regarding the 80 degree procedure turn. For instance if the inbound track is 360 and there is an 80 degree procedure turn to the right, wind in 090/15, I am told that there is a rule of thumb where by you hold that heading say 080degrees for so many seconds, on the other hand if the wind was 270/15 you do not turn onto a Hdg080 but some lesser Hdg so that you don’t get blown to far down wind. Can you remember such a rule??
Thanks for that, just one more question. Regarding the 80 degree procedure turn. For instance if the inbound track is 360 and there is an 80 degree procedure turn to the right, wind in 090/15, I am told that there is a rule of thumb where by you hold that heading say 080degrees for so many seconds, on the other hand if the wind was 270/15 you do not turn onto a Hdg080 but some lesser Hdg so that you don’t get blown to far down wind. Can you remember such a rule??
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Some food for thought
Regarding drift allowance in the holding pattern, was lucky enough to attend a lecture about twelve years ago by a guy ( whose name escapes me ) who was one of two blokes in the " Department " at the time whose job it was to design new approaches. He was quite positive about his views on drift correction in the holding pattern and that was that " triple the drift " for a 2 min pattern and " double the drift " for a 3 min pattern were not approved procedures.
In correcting for a wind that blows you into the pattern what you are actually doing on the outbound leg is purposely flying the aircraft wide and in doing so you could leave the protection of the surveyed area with regards to obstacle clearance.
ENR 1.5 3.4.1 states;
" When flying the standard holding pattern , an aircraft MUST;
a. follow the prescribed track inbound to the holding point;
b. execute a 180 turn in the direction specified , SO AS TO FLY
OUT-BOUND A TRACK PARALLEL TO THE INBOUND TRACK;
c. continue outbound to the earlier of the time, or the DME limit
specified ; and
d. execute a 180 turn to realign the aircraft on the inbound track."
Paragraph "b" is quite explicit , you MUST fly the outbound leg so as to parallel the the inbound track , no mention of "triple" or "double" the drift. It was made clear to all at the lecture that all you are permitted to do on the outbound leg is apply the known drift in order to keep the leg parallell
Perhaps someone involved at this level of approach design today could be found to comment.
Regards Mr Gaspo
In correcting for a wind that blows you into the pattern what you are actually doing on the outbound leg is purposely flying the aircraft wide and in doing so you could leave the protection of the surveyed area with regards to obstacle clearance.
ENR 1.5 3.4.1 states;
" When flying the standard holding pattern , an aircraft MUST;
a. follow the prescribed track inbound to the holding point;
b. execute a 180 turn in the direction specified , SO AS TO FLY
OUT-BOUND A TRACK PARALLEL TO THE INBOUND TRACK;
c. continue outbound to the earlier of the time, or the DME limit
specified ; and
d. execute a 180 turn to realign the aircraft on the inbound track."
Paragraph "b" is quite explicit , you MUST fly the outbound leg so as to parallel the the inbound track , no mention of "triple" or "double" the drift. It was made clear to all at the lecture that all you are permitted to do on the outbound leg is apply the known drift in order to keep the leg parallell
Perhaps someone involved at this level of approach design today could be found to comment.
Regards Mr Gaspo
Lots of people advocate the double or triple drift idea, but if you do that you're not correcting for known or forecast wind to maintain the planned track, you're aiming to fly a track different to the one on the plate - ie. a holding pattern with non-parallel straight legs, which to me isn't right, so I use single drift and adjust the bank to get the turns right.
It's a bit of a catch-22 though, because if you do apply drift to fly the 'right' track as per the plate you're stuck with varying the turns at each end away from rate 1, going against what the AIP says.
It's a bit of a catch-22 though, because if you do apply drift to fly the 'right' track as per the plate you're stuck with varying the turns at each end away from rate 1, going against what the AIP says.
Mr Gaspo you beat me to it. Thank you.
The Jepps and AIP are VERY specific, you MUST plan to fly the OUTBOUND LEG parallel to the inbound leg, no correspondence will be entered in to!
It doesn't matter if that is what you were taught.
It doesn't matter if that is what you have always done.
It doesn't matter if a bloke in the bar knew someone at Qantas who did it that way.
End of story.
The Jepps and AIP are VERY specific, you MUST plan to fly the OUTBOUND LEG parallel to the inbound leg, no correspondence will be entered in to!
It doesn't matter if that is what you were taught.
It doesn't matter if that is what you have always done.
It doesn't matter if a bloke in the bar knew someone at Qantas who did it that way.
End of story.
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The problem with that being that if you do fly a parallel track outbound in strong crosswind conditions, you have precisely no hope of regaining the inbound track without exceeding your max bank angle. Using the information described above in a crosswind situation,the only decision you have to make is which parameter you want to exceed, outbound trackkeeping, inbound trackkeeping, or bank angle.
My view is that the rule is written for still-air, and the obstacle clearance plane is in any case well outside the point where you would turn inbound, using a rate one turn, to regain the inbound track in any conceivable crosswind. Hold tolerances are simply not that tight, and where obstacle clearance is limiting, the outbound limit is defined by a DME distance or cross-bearing (or both).
My view is that the rule is written for still-air, and the obstacle clearance plane is in any case well outside the point where you would turn inbound, using a rate one turn, to regain the inbound track in any conceivable crosswind. Hold tolerances are simply not that tight, and where obstacle clearance is limiting, the outbound limit is defined by a DME distance or cross-bearing (or both).
Drift
Some of you guys should enlighten yourselves a bit more than just reading the Oz publications. Read the Jeppesen ATC booklet under the United States Page 1. for holding patterns. It says drift time 3.It also explains why.
That'd be very relevant if we were all flying in the USA, but we're not, so we must comply with the Australian requirements, regardless of whether they are the best way of operating or not. Ideally, if they're not the best, then we need to get the publications changed to match what the safe and practical practice is.
We also don't all have access to the US Jepps.
We also don't all have access to the US Jepps.
Which part of parallel do you have difficulty understanding?
MBA747, as Aerocat says, we fly to our AIP/Jepp requirements. Should we also not use supplemental oxygen until (is it) FL140, as per US rules. Obviously our air here is thinner, but it does seem to help our comprehension skills.
MBA747, as Aerocat says, we fly to our AIP/Jepp requirements. Should we also not use supplemental oxygen until (is it) FL140, as per US rules. Obviously our air here is thinner, but it does seem to help our comprehension skills.
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OK smartarse, please explain how, using exactly parallel inbound and outbound tracks, using no more than 25 degrees AoB with a 50kt crosswind, you have any chance at all of regaining the inbound track. You CAN'T. Simple trigonometry.
More to the point, Australian procedures are based on PANS OPS II, which does NOT require parallel inbound and outbound tracks.
(My bolding)
There is no "difference" listed for Oz procedures.
Now why not try using a little common sense rather than a slavish obedience to the wording of a single reference? Ever heard of context?
Update: The Oz AIP says this:
"3.2.1.e - Wind Allowance. Allowance should be made in heading and timing to compensate for the effects of wind to ensure the inbound track is regained before passing the holding fix inbound. Full use should be made of indications available from the aid and estimated or known winds."
The point being that the priority is to regain the inbound track. You can't do that with a symmetrical holding pattern in a strong crosswind because of the limiting AoB (25 degrees).
I can't believe I was reduced to reading the AIP in my spare time...
More to the point, Australian procedures are based on PANS OPS II, which does NOT require parallel inbound and outbound tracks.
2.2 Controls
2.2.1 The controls that apply to procedure design and DAP administration are listed in the
following references:
l ICAO PANS-OPS (Doc 8168), Volume II
l ICAO Template Manual for Holding, Reversal and Racetrack Procedures (Doc
9371)
l ICAO Manual on the Use of the Collision Risk Model (CRM) for ILS Operations
(Doc 9274)
l ICAO Instrument Flight Procedures Construction Manual (Doc 9368)
l CASA Manual of Operational Standards (MOS)
l CASA Aviation Safety Surveillance Program (ASSP)
l Airservices Australia Flight Survey Manual.
n
2.2.1 The controls that apply to procedure design and DAP administration are listed in the
following references:
l ICAO PANS-OPS (Doc 8168), Volume II
l ICAO Template Manual for Holding, Reversal and Racetrack Procedures (Doc
9371)
l ICAO Manual on the Use of the Collision Risk Model (CRM) for ILS Operations
(Doc 9274)
l ICAO Instrument Flight Procedures Construction Manual (Doc 9368)
l CASA Manual of Operational Standards (MOS)
l CASA Aviation Safety Surveillance Program (ASSP)
l Airservices Australia Flight Survey Manual.
n
There is no "difference" listed for Oz procedures.
Now why not try using a little common sense rather than a slavish obedience to the wording of a single reference? Ever heard of context?
Update: The Oz AIP says this:
"3.2.1.e - Wind Allowance. Allowance should be made in heading and timing to compensate for the effects of wind to ensure the inbound track is regained before passing the holding fix inbound. Full use should be made of indications available from the aid and estimated or known winds."
The point being that the priority is to regain the inbound track. You can't do that with a symmetrical holding pattern in a strong crosswind because of the limiting AoB (25 degrees).
I can't believe I was reduced to reading the AIP in my spare time...
Last edited by MOR; 14th Jun 2006 at 06:43.
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MOR ,
You raised some interesting points and if I may I'd like to comment on some of them.
After spending a few minutes on my WIZZ-WHEEL to nut out your 50 Kt crosswind problem in the holding pattern in say something like a warrior with lets say a tas of 100 Kt's , I come up with a correction angle of 90 degrees for a one minute pattern!!!!!
On your point concerning the holding pattern not being symmetrical , after having viewed all of the post's up to your one , and after reviewing the AIP re-holding patterns , I may have missed something but can't find any mention of "symmetrical" other than in your post. No one has said (AIP included) that the holding pattern must be symmetrical , only that the out-bound leg should parallel the inbound leg.
You seem to be of the opinion that it is a requirement to regain the inbound leg at the beginning of that leg , it isn't. This is explained in your reference to ENR 1.5 3.2.1
"allowance should be made in heading and timing to compensate for the effects of wind to ensure the inbound track is regained BEFORE passing the holding fix inbound"
This actually precludes a symmetrical pattern in all but nil wind conditions. There is a completely separate method of correcting for wind in the holding pattern that I have been using for over twenty years of teaching them and yes, it's based on trigonometry. But I dont want to give that away just yet, I'm curious as to whether any other PPruners' have any suggestions.
You raised some interesting points and if I may I'd like to comment on some of them.
After spending a few minutes on my WIZZ-WHEEL to nut out your 50 Kt crosswind problem in the holding pattern in say something like a warrior with lets say a tas of 100 Kt's , I come up with a correction angle of 90 degrees for a one minute pattern!!!!!
On your point concerning the holding pattern not being symmetrical , after having viewed all of the post's up to your one , and after reviewing the AIP re-holding patterns , I may have missed something but can't find any mention of "symmetrical" other than in your post. No one has said (AIP included) that the holding pattern must be symmetrical , only that the out-bound leg should parallel the inbound leg.
You seem to be of the opinion that it is a requirement to regain the inbound leg at the beginning of that leg , it isn't. This is explained in your reference to ENR 1.5 3.2.1
"allowance should be made in heading and timing to compensate for the effects of wind to ensure the inbound track is regained BEFORE passing the holding fix inbound"
This actually precludes a symmetrical pattern in all but nil wind conditions. There is a completely separate method of correcting for wind in the holding pattern that I have been using for over twenty years of teaching them and yes, it's based on trigonometry. But I dont want to give that away just yet, I'm curious as to whether any other PPruners' have any suggestions.
Jepps.
The point I was trying to make, it was the only place I have seen where this is recommended ie. 3 times drift. A holding pattern is the same in any part of the world. It sometimes pays to read other publications,it makes one a lot more informative. Apart from CPDLC and ADS we are in the backwaters when it comes to aviation.
The other points about symmetrical holding patterns, yes they can be flown quite easily provided you are in an aircraft which has an FMC and where the ADIRU position is not only updated by navaids but also GPS. Modern aircraft now have an RNP1 with an ANP0.3 the holding patterns are nearly perfectly symmetrical. Aircraft flown in LNAV.
The other points about symmetrical holding patterns, yes they can be flown quite easily provided you are in an aircraft which has an FMC and where the ADIRU position is not only updated by navaids but also GPS. Modern aircraft now have an RNP1 with an ANP0.3 the holding patterns are nearly perfectly symmetrical. Aircraft flown in LNAV.
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MrGaspo
I was using "symmetrical" to describe two parallel lines/tracks, but, sure, it isn't precisely the right word.
No, I'm not of that opinion, quite the reverse. My point is that if you attempt to fly a parallel outbound leg and then fly through the inbound track because you have a large crosswind component and a limiting bank angle, you no longer have two parallel tracks as the track to regain the inbound course will no longer parallel the outbound leg you just flew. It should be obvious that the inbound tracking is more important than the outbound, particularly if you end up never regaining the inbound track before you get to the fix or beacon. Common simulator scenario.
I was looking at the problem more from the point of view of jet speeds and bank angles, as the altitudes we fly at are more likely to produce the crosswinds I was describing, and also produce a more limiting bank angle. However, the principle is the same for light aircraft.
I was using "symmetrical" to describe two parallel lines/tracks, but, sure, it isn't precisely the right word.
You seem to be of the opinion that it is a requirement to regain the inbound leg at the beginning of that leg , it isn't. This is explained in your reference to ENR 1.5 3.2.1
I was looking at the problem more from the point of view of jet speeds and bank angles, as the altitudes we fly at are more likely to produce the crosswinds I was describing, and also produce a more limiting bank angle. However, the principle is the same for light aircraft.