Holding: Time correction

[minibus3]

Hi Guys/Girls,

I'm looking for an easy (something you should be able to do in your head!) way to calculate a time correction to the outbound leg of a holding pattern, given the course and the W/V so that you end up with the desired 1 min (or 1.5 min) inbound.

E.g. if the inbound course is 143 deg., and the W/V is 010/24, what initial time should be used for the outbound leg.

Obviously once you get into the hold it's trial and error, but this is just for an initial guesstimate upon entering the hold.

The searches didn't come up with what I was looking for.

Cheers:ok:

[Brain Potter]

Add half-a-second per knot of head wind component outbound. Or 1 sec per 2 knots (whichever way you want to think of it). Subtract for tailwind outbound in a similar manner.

In your case the wind is 47 degrees off the nose on the outbound leg, giving 16 knots of headwind. Time for 1 min 8secs from the abeam radial or wings level, whichever is later.

[bfisk]

Whip out your fantastic E6B wind side - 1x the WCA inbound and a little less than 3x the WCA outbound.

:)

[keithl]

BPotter is right. Bfisk didn't RTFQ!

[minibus3]

Brain Potter - thanks for the answer, very much appreciated.:D

keithl - your correct aswell!

Cheers

[SB4200]

G'day Brain Potter

Interestingly i've always been taught 1 second per knot (as opposed to 1/2 second per knot). Would someone out there smarter than me be able to run the numbers and prove/disprove either theory?

I guess it must depend on TAS to some extent. How about for typical Cat B speeds. Perhaps the above is for a faster (higher Cat) aircraft?

[Brain Potter]

I still remember being taught to use 1/2 sec per knot on slow training aircraft.
Here is my theory :8 - feel free to argue, I made it up today.
As I see it the timing outbound is trying to achieve a consistent point above the ground to commence the turn inbound; in much the same way as DME-based holds work.
This "proof" assumes that the wind effects in turns cancel each other out. (?)
A 20 knot headwind will leave any aircraft 1/3 mile short of it's normal 1 minute still-air point (20 kts = one third of a mile per minute).
An aircraft holding at 210 KIAS (3.5 nm/min) will make up this distance in 6 seconds at 190 knots groundspeed. The inbound 3.5 miles will then take 54 seconds at 230 knots groundspeed, giving a total time for the 2 straight legs of 2 mins. Thus the timing adjustmnt should be 6 secs.
An aircraft holding at 120 KIAS will make up the shortfall distance in 12 seconds at 100 knots groundspeed. The inbound 2 miles will then take 51 secs at 140 knots groundspeed, giving a total of 2 mins 3 secs for the straight legs. Hence the timing adjustment should be 12 secs.
This method implies that the most accurate timing would be obtained by dividing the headwind component by the holding IAS in nm/min ie at 210 kts divide the 20 knots HW by 3.5 nm/min to get a 6 secs adjustment. A 10 second adjustment is pretty close to both cases and gets the simplicity vote. Clearly a 20 sec adjustment is too much.
It may be that the universal dividing by 2 rule is close enough for all aircraft and that, in practice, the effect of wind in turns may be significant. Perhaps it has just been obtained empirically. However, for what it's worth, the above examples at least show that 1 sec per knot is too much - even on slow aircraft.

[SB4200]

All valid and logical points Brain. Thanks for the discussion. I'm not sure where the 1 second per knot rule has come from but will investigate further and report back...

Cheers

[nightowl727]

.... This "proof" assumes that the wind effects in turns cancel each other out. (?)
A 20 knot headwind will leave any aircraft 1/3 mile short of it's normal 1 minute still-air point (20 kts = one third of a mile per minute).
An aircraft holding at 210 KIAS (3.5 nm/min) will make up this distance in 6 seconds at 190 knots groundspeed. The inbound 3.5 miles will then take 54 seconds at 230 knots groundspeed, giving a total time for the 2 straight legs of 2 mins. Thus the timing adjustmnt should be 6 secs ....
What about correction for the displacement during 2 minutes of turns? Not familiar with that particular ROT, but maybe the full 1 second/kt adjustment takes the entire racetrack into account?

Cheers, nightowl :ok:

[AHRS]

Timing is all well and primary as reference but when flying you OUGHT to apply flying thinking and intuition and don't allow your brain space to be clogged with much calculations amd similar paraphanelia(it will distract you from the primary task of basic instrument flying) that is why you find rules of thumb being applied by old hats!
There is a holding slide rule computer if you wish to be fastidious and wish to free your cognitive space, but the actual turning point towards the inbound axis may be defined by time but it is dictated by your ground position relative to the inbound axis and the holding fix.You can never be 100% exact by depending upon time corrections alone as you have to have a precise read out of your GROUND SPEED.I often manage to get the 3 minute(and that is what matters rather the 4 minutes)-time from abeam or upon reaching outbound track(outbound heading corrected for w/v) whichever is earlier and keeping an eye on the relative bearing of the holding fix upon reaching 30 degrees off the tail whence one commences a standard rate turn(bank angle depends upon TAS).
IT ALL SOUND RATHER COMPLEX BUT WITH PRACTICE AND EXPERIENCE YOU JUST DEVELOP THE RIGHT HUNCH AS TO WHEN AND FOR HOW LONG TO DO WHAT IS NECESARY...BUT BASIC INSTRUMENT FLYING FOCUS COUPLED WITH RADIO NAV REFERENCE HAS TO BE ENFORCED.I advise that much money and toil can be saved by practicing on a simulator (even MSFS!) AND ONCE CONFIDENT AND CONSISTENT TO GO UP THERE AND TEST YOUR SKILLS.

An important feature of executing the hold is visualization of the inbound axis and the relative w/v and maintainig a constant flying speed and consistent wind corrected tracks as well as maintaining the standard rate turns consistent with appropriate bank angles.Remember also the rules for holding at different flight levels and different speeds(jets vs props) demand different times.Review your AIP and better still review the procedures at cruise prior to descent when a holding is possible-which can be anticipated if you pay attention to the RTF and visualize how the traffic is being managed.

Happy holdings! http://www.pprune.org/forums/images/icons/mpangel.gif...and be smooth about it!!!

Hi Guys/Girls,

I'm looking for an easy (something you should be able to do in your head!) way to calculate a time correction to the outbound leg of a holding pattern, given the course and the W/V so that you end up with the desired 1 min (or 1.5 min) inbound.

E.g. if the inbound course is 143 deg., and the W/V is 010/24, what initial time should be used for the outbound leg.

Obviously once you get into the hold it's trial and error, but this is just for an initial guesstimate upon entering the hold.

The searches didn't come up with what I was looking for.

Cheers:ok:

[keithl]

On the question of whether it should be 1 sec/knot of wind or 1 sec/2kts wind, I once calculated (can't remember how, and don't have the energy to repeat it!) that it worked out at 1sec per 1.5 kts of wind. Therefore both approximations are right. And that is the important point. It is an approximation, a Rule of Thumb, that will give your first hold a fighting chance of being in the right area. After that, as the minibus said, its trial and error anyway.

[Rainboe]

I've always used 1 sec/kt wind component. If it is regarded as too much, maybe it is because you need to correct for the turns too when you are in the hold proper doing complete patterns. Now you just leave it for the FMS to do- terribly depressing to see it making a better job.

[keithl]

Now you just leave it for the FMS to do

Not where I work, Rainboe. "The Craft" is still alive, if you know where to find it...

[Empty Cruise]

Surely you are not talking about correcting the outbound timing so as to achieve a 1 min. inbound leg???

A careful re-read of ICAO Doc 8168 might be in order - just imagine an aircraft with a 220 KIAS holding speed holding with 100 kt. headwind outbound, GS inbound would be 320 kt, so our man/gal would need a 5,2 NM inbound leg + correction for drift during the turn, call that another 1,5 NM - and suddenly, a standard ICAO holding pattern will now need an outbound timing of almost 3,5 minutes... :ouch:

This is not what holdings were designed for - stay inside the design parameters, and don't give a toss about the timing inbound, you'll know when you pass the fix anyhow. The outbound timing should only be corrected for W/V in order for you to stay inside the primary holding area, not so you can impress anyone with an inbound timing from wings level to fix of exactly one minute. :ugh:

Stay safe :ok:

[minibus3]

Empty Cruise - I'd appreciate it if you could elaborate on how you go about this:
stay inside the design parameters, and don't give a toss about the timing inbound, you'll know when you pass the fix anyhow. The outbound timing should only be corrected for W/V in order for you to stay inside the primary holding area
Thanks

[nightowl727]

.... This is not what holdings were designed for - stay inside the design parameters, and don't give a toss about the timing inbound, you'll know when you pass the fix anyhow. The outbound timing should only be corrected for W/V in order for you to stay inside the primary holding area, not so you can impress anyone with an inbound timing from wings level to fix of exactly one minute ....
Sometimes it pays to impress ones instructors :E

IAC, here in Canada, hold timing is proscribed as follows [from TC AIM]:
10.6 Timing
The still air time for flying the outbound leg of a holding pattern should not exceed 1 minute if at or below 14 000 feet, or 1 1/2 minutes if above 14 000 feet ASL; however, the pilot should make due allowance in both heading and timing to compensate the wind effect.
After initial circuit of the pattern, timing should begin abeam the fix or on attaining the outbound heading, whichever occurs later. The pilot should increase or decrease outbound times, in recognition of winds, to effect 1 or 1 1/2 minutes (appropriate to altitude) inbound to the fix.
When the pilot receives ATC clearance specifying the time of departure from the holding point, adjustments should be made to the flight pattern within the limits of the established holding pattern to leave the fix as near as possible to the time specified.
I expect the CAA/JAR rules are similar. Notwithstanding that, controllers are not usually timing your inbounds, but likely are minding the airspace you're using. Away from a pedantic instructor's gaze, timing for simple four minute race-tracks works well. Advantages:

[1] - the largest race-track is the no-wind one (confining your airspace use).
[2] - timing is simple: after flying a 1-minute outbound circuit, add/subtract half the time-change needed on the outbound leg.
[3] - planning for station passage at EFCTime is much easier.

Disadvantages (other than instructor/legal-beagle carping ;)): .... ?

Cheers, nightowl :ok:

[keithl]

Before everyone goes off at a tangent, I'd just like to point out that different states/regions have different interpretations of ICAO holding rules. Sorry, they aren't 'rules', they're recommendations.

I'm aware, from training pilots who have gone through various basic IR courses around the world, that in some places (esp. USA) the teaching is to achieve a one minute inbound leg. In other places (e.g. UK) the outbound timing is adjusted to achieve 3mins from abeam to on-top the beacon. I have also heard of other places where you may extend the outbound timing, but never reduce it below 1min.

In short, I'd support Empty Cruise's statement that the important thing is to stay inside the cleared area of the hold. I have my own opinions on the various interpretations, but that would be getting away from minibus's question. As one of those instructors who has to be impressed, I'd say as long as you know what's going on and make sensible corrections, I'll be impressed.

[minibus3]

Maybe a little more information would be of use?:
I'm fly the hold at 90 KIAS, and operate in US airspace.
If anyone has any other contributions, I'm all ears:
I'll also note here that the original query related to achieving a defined inbound leg, and that nobody has actually specifically addressed that
Would you care to provide some info RE this nightowl?
I should also make myself clear, and say that this "rule of thumb" is just for an approximation, to get an idea of what to expect of the trial and error. And of course, Empty Cruise, the important things is to stay within the protected area - that's the idea(?).
Cheers, m'3

[Sabre-Rattler]

Use the FMC :E

[nightowl727]

OOPS - Sorry, minibus, I deleted my last posting while you were putting yours up (a bit too argumentative ;)) . The truth is, I don't have a good ROT for achieving 1 minute inbound. It is a tricky and rather pointless exercise, as has been said here already - and one that provides much frustration for instructor and student (and transfer of treasure :}). When do the times start? outbound, abeam or wings level, inbound, at intercept or wings level, etc. etc. As trial and error eventually finds the slot, probably any intuitive guess will shorten the process. The 1 sec/kt (or 2kts?) is probably as good as any, altho' mathematically any precise adjustment would have to account for airspeed. Indeed, I think most of the attraction of these little ROT's is a search for an arithmetic elegance, rather than any real, demonstrable benefit.
If you are not required to achieve a defined inbound time in your jurisdiction, I'd follow the advice here to use a simpler method to organise your time and track.
Use the FMC :E
Indeed! - If one is available :(
Not where I work, Rainboe ...
Nor where I ... :rolleyes: ... We seem to find our way around the holds, tho'. As was rightly pointed out, it's all recommendation anyway; note the frequent use of "should" in the TC AIM excerpt above - there'll be no enforcement of the 1-minute inbound (in Canada - not sure about the FAA). As for check-rides, I've never seen a pilot busted for not achieving the inbound time, but I have witnessed some stern debriefings about it, so it still behoves a candidate to "impress" :ugh:
Cheers, '27 :ok:

[minibus3]

No worries nightowl - thanks for your contribution.
I agree with you.
The 1 sec/kt (or 2kts?) is probably as good as any
Just for the record - 1sec./kt seems to work fairly well.
When do the times start? outbound, abeam or wings level, inbound, at intercept or wings level
I usually use abeam OR wings level, whichever is latest.
Use the FMC
Exactly:ok: - but unfortunately my Piper doesn't have one!
Cheers, m'3

[bookworm]

I expect the CAA/JAR rules are similar.
No, they're not, which is why you're seeing some divergence of answers. PANS-OPS says:
1.3.3 Allowance for known wind
All procedures depict tracks. Pilots should attempt to maintain the hack by making allowance for known wind by applying corrections both to heading and timing. This should be done during entry and while flying in the holding pattern.
1.3.4 Start of outbound timing
Outbound timing begins over or abeam the fix, whichever occurs later. If the abeam position cannot be determined, start timing when the turn to outbound is completed.
1.5.2 Corrections for wind effect
Due allowance should be made in both beading 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 navaid and estimated or known wind.
Going for a 1-minute inbound leg is a North American thing. It requires a 1.5 sec/knot correction at 120 KTAS. One could argue that PANS-OPS allows an outbound distance equivalent to 1 minute in still air (0.5 sec/knot at 120) or an extended outbound to make the start of the inbound leg at the equivalent still-air position (1.0 sec/knot at 120).
(As a simplistic explanation, 0.5 sec/knot at 120 compensates for the wind on a 1 minute leg, 1.0 sec/knot at 120 compensates for the wind on a 1 minute leg + a 1 minute turn, 1.5 sec/knot at 120 compensates for the wind on a 1 minute leg + a 1 minute turn + the 1 min inbound leg).
Just noticed that keithl has posted similarly about procedures being different. For a 3 minute total from abeam, it's 0.75 sec/knot.

[nightowl727]

No, they're not, which is why you're seeing some divergence of answers. PANS-OPS says ....
Just noticed that keithl has posted similarly about procedures being different.
Yes, difference duly noted - also that the query arose from American practice. Regarding my erroneous assumption, please forgive a benighted colonial; that whole timed-inbound-leg fandango, which over here we are admonished to perform, is so eccentric and obtuse, I just assumed it had to be originally a British thing :}
Cheers, '27 :ok:

[keithl]

Well, I understand that assumption, 'owl, but not guilty on this occasion.

I agree the "one minute inbound" is rather pointless. After all, the outbound leg is the ONLY place where corrections are possible.

[Brain Potter]

Empty cruise Surely you are not talking about correcting the outbound timing so as to achieve a 1 min. inbound leg???

The examples I gave for outbound timings were to illustrate the leg-length required to achieve a turn inbound at a point co-incident with the end of a 1-min outbound leg in still-air. I believe this is the best way of keeping the ground track of holding pattern as close to the still-air racetack pattern as possible. I think that 1 sec for every 2 knots HW is the best compromise between simplicity and accuracy.
I seem to remember that in basic training I was taught to commence timing from the latter of wings level/abeam radial and then note the elapsed time back over the beacon. If the time was greater than 3 mins, the error was halved and subtracted from the previous outbound timing. Similarly, if the time was less than 3 mins, the error was halved and added on. The aim was to achieve a consistent 3-min outbound/turn/inbound segment.
I agree that achieving a 4-minute hold doesn't really matter per se and the aim of the Mental Dead Reckoning is only to ensure that the aircraft stays within the protected area, when there is only an NDB available to fix postion. An FMS or GPS groundtrack achieves this much more accurately than any MDR process. Some larger/faster aircraft are limited to 25 degrees of bank in the turn and hence cannot achieve a Rate 1 turn. The holding pattern will actually take nearer to 5 mins due to longer turns, as is the case with my current aircraft. We don't bother to refine the timing using the previous error, and simply recalculate each time once steady outbound using 1 sec per 2 knots of HW - but that is the great advantage of having an instantaneous wind calculated by INS/FMS.

[Apache36]

IACO rules require a 1 minute outbound leg and don't care what the inbound time is which is much simpler than FAA rules but somewhat less precise. FAA rules require 1 minute inbound leg which is where trying to adjust the outbound leg gets tricky.

My method is to fly the first outbound leg for 1 minute from the abeam point. Then time the inbound leg from the point that I intercept the inbound course line if I fly through it, or wings level on course inbound. If the inbound time is 70 seconds, I know I had a tail wind going outbound. I whip out my trusty E6B and place the 70 second mark under the 60 second mark. The index pointer then points at the new time (51 seconds)I need to fly outbound, which in this case makes sense. I have to shorten my outbound time to allow for the tailwind to get my inbound time down to the 60 second target.