NoyGonnaDoIt

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5. Distance Measuring Equipment (DME)/ GPS Along-Track Distance (ATD). DME/GPS holding is subject to the same entry and holding procedures except that distances (nautical miles) are used in lieu of time values.
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OHPilot213

I usually tell students just use the one minute then once established use the 4nm for the legs ... lets say you used a teardrop entry and flew out for 4nm, you would have to make one really shallow turn to come back in to intercept that inbound course ... if you stick with the 1 minute entries its just fly out for 1 minute then should be right about a standard rate to intercept your inbound course which establishes you in the hold ... just my .02 and what i tell my guys to do i think its easiest ... no references sorry

USMCFLYR

This was the topic of discussion just yesterday in my office. I had also taught what you state above OHPilot213, but after further review yesterday into the Instrument Flying Handbook and the AIM, and keying in on the points made by FBK and NGDI above, I think that I was mistaken in teaching such. I htink that way was appropriate when GPS was not available, but I think that now if a DME / leg length is dictated then the ENTRY into the holding pattern should be flown referencing the NMs.

USMCFLYR

OHPilot213

Ok, the only problem I had with that is if I do lets say a teardrop entry like i said earlier, if i fly outbound for 4NM it will probably take me a lot longer than 1min in most single engine trainers. When you go to make a turn back to intercept the inbound course you really would not know how steep/shallow to make the turn so it can be relatively continuous, If you use the 1 minute outbound for the entry then it should be a consistent and continuous bank standard rate turn back to intercept the inbound course. Also when the 4NM is depicted on a GPS approach plate it usually has a line on the outbound leg at the end of the leg, my interpretation is that this is the point in the hold where you should be 4NM from the fix you are holding around, not at any other point during the hold including the entry. Not sure what others think, I just need a little more convincing evidence and reference before I teach it a different way, plus my method works and I know many others that teach it my way too.

USMCFLYR

As others have said though - the leg has now been defined for *some* reason. Yes - when it was a timing problem, the 1 minute outbund during the entry would set you up close the required holding time for the inbound leg, then you adjusted accordingly for the proper timing.
For *some* reason now - they want you to fly a 4 mile leg. So you fly out to the 4 miles, turn inbound with an intercept heading and you find yourself on an approx 4 nm leg inbound. I don't remember a constant rate turn on a teardrop putting you right back on the inbound course in case. I thought you took a 30 deg cut back to the inbound course and intercepted it. I remember a no-wind, perfectly flown (constant airspeed and AOB) 90/270 doing that
Yep - I taught it your way to in the past. Personally - I think I was wrong now. Not that I will be teaching anybody - anything for a long time, but I would use the aforementioned references and change my approach if I found myself in such a position. I understand your position though and I'm just on the other side of it. I know need more convincing that it is the *other* way.
If I get a chance through, maybe I'll do a little more indepth research and see if I can come up with some more information one way or the other.

USMCFLYR

clipperstall

I just developed a holding pattern and placed a fix exactly 4NM and (30 degrees off the inbound course) in the location of where a teardrop entry would take place using the smallest template that TERPS currently uses. In this instance, the 4NM spot (located in the protected side of the pattern) does not exceed the limits of the holding template.

If your equipment allows, it would be perfectly safe to get a dme/gps readout directly from the entry fix.

Likewise, timing also would suffice considering we use very similar (sometimes the same) template sizes based on airspeed as well.

Both methods would keep you in the protected area which is the whole intent of a holding pattern.

If you continue reading that same passage on 5-3-13 of the AIM, it says "Some GPS overlay and early stand alone procedures may have timing specified." So timing MIGHT be used on a GPS hold rather than distance. It just depends.

Fly Boy Knight

When I used to teach, I used to teach simply using 1 min for the entry as well o0n a 4NM GPS Hold but, like USMC, I believe the texts show more support for the 4NM entry leg, regardless of entry type (TD or P).

It seems kind of over-kill in my mind to fly OB for 4NM on a teardrop entry but the only thing that is 100% definitive in the AIM about this topic is as long as you remain within the 4NM barrier, you will be protected. I suppose the FAA and NACO design the hold procedures to account for this 4NM TD entry type.

Maybe the AIM's procedure not to exceed 200 KIAS during a procedure turn (and a hold in lieu of a PT I would assume as well) helps to keep you from straying to far away from the Inbound Course when doing a teardrop entry.

Clear as mud lol

NoyGonnaDoIt

True enough. If the chart or the clearance doesn't mention distance, you use time, GPS or no GPS. That was especially true in the early overlays and GPS approaches that were essentially overlays put on their own piece of paper. They were already timed holds. No need to change them at that stage. Probably aren't too many of those left anymore.

The issue that got me interested in the question is not so much the distance v. time argument about entries but varying published distances. There are, for example, two GPS approaches in the Denver area that have 7 NM holds associated with them rather than the more common 4 NM. One is the co-located HILPT and missed hold for the KAPA GPS 28; the other is the missed hold for the KBJC GPS 29R.

That's what got me to thinking. Why 7 instead of 4? I'm not satisfied with my own guess that it allows for ATC to let other aircraft "cut across" the hold without losing IFR separation based on where the holding aircraft is expected to be. Sounds too dicey. But it still leave the question for me of why the differing sizes.

As someone who works in this area, do you have some guidance for an answer?

clipperstall

The 7 was used instead of 4 because of the altitude that you are holding at those fixes. When you hold at a higher altitude (per FAA criteria) there tends to be more terrain issues and the aircraft tend to be faster with larger turn radii. As a result we use a larger template size which causes us to evaluate a larger area. The larger area is directly associated with the DME or GPS distance associated with the hold.

When we design the holding pattern on an approach, all we do is look up what altitude we want to develop the pattern at (which is determined by obstacles, terrain, or air traffic request). Then we look up what template size based on the speed and altitude of aircraft. Then we choose the corresponding leg length.

These leg lengths were developed in criteria meetings in Flight Standards which determine what is considered "safe" design.

For example (Per regulation 7130.3a): A hold at 4000 and 200KTS tells us to use a pattern 5 on a GPS approach. Pattern 5 templates require a 4NM leg length.

I hope that clears it up.

NoyGonnaDoIt

Hmm. Distance based on msl rather than AGL? Interesting. Speed limits are based on AGL But I do see that according to the AIM, max holding speeds are based on msl.