Holding: Time correction
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Join Date: Oct 2004
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No worries nightowl - thanks for your contribution.
I agree with you.
Just for the record - 1sec./kt seems to work fairly well.
I usually use abeam OR wings level, whichever is latest.
Exactly
- but unfortunately my Piper doesn't have one!
Cheers, m'3
I agree with you.
The 1 sec/kt (or 2kts?) is probably as good as any
When do the times start? outbound, abeam or wings level, inbound, at intercept or wings level
Use the FMC
- but unfortunately my Piper doesn't have one!Cheers, m'3
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.
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.
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Cheers, '27
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.
I agree the "one minute inbound" is rather pointless. After all, the outbound leg is the ONLY place where corrections are possible.
Join Date: Aug 2003
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Empty cruise
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.
Surely you are not talking about correcting the outbound timing so as to achieve a 1 min. inbound leg???
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.
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different rules
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.
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.
