Why is the max speed for a hold faster when climbing?

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qwerty123
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Why is the max speed for a hold faster when climbing?

#1 Post by qwerty123 » Sat Dec 09, 2017 6:26 pm

I've been studying for my INRAT and going through the AIM I noticed the max speeds for a hold are:
Prop: 175 KIAS
Turbojet below 14,000 ft: 230 KIAS
Turbojet above 14,000 ft: 265 KIAS

But while climbing in a hold the max speeds are:
Prop: normal climbing speed
Turbojet: 310 KIAS
(AIM RAC 10.7)

Any idea why turbojets can go 45 knots faster while climbing? It seems odd that the speed limitation is different just because you're climbing.
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Re: Why is the max speed for a hold faster when climbing?

#2 Post by AuxBatOn » Sat Dec 09, 2017 7:24 pm

I'd say it has to do with fuel efficiency in the climb but I am not sure.
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confusedalot
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Re: Why is the max speed for a hold faster when climbing?

#3 Post by confusedalot » Sat Dec 09, 2017 8:46 pm

Now that is a very good question; after all this time I never caught on to the discrepancy.

I will only assume that if a holding clearance was issued and the plane was in a climb prior to the holding point, typically, a jet will be at 290 KTS or greater at normal climb speed, so I figure that the authorities cut them some slack and permitted the maximum to be at 310 KTS while still climbing? I dunno. Otherwise, the crew would need to either reduce thrust in a climb or significantly increase their pitch attitude to get to 265 KTS, both of which would be undesirable.

Really, I am only guessing.
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Re: Why is the max speed for a hold faster when climbing?

#4 Post by kevenv » Sun Dec 10, 2017 7:38 am

Maybe more to do with the airspace to be protected for the hold. Once established in the hold the fix end reduction area can be dropped making the size of the protected area smaller. I am assuming that the initial template for the hold covers the higher speeds given.
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Re: Why is the max speed for a hold faster when climbing?

#5 Post by AuxBatOn » Sun Dec 10, 2017 7:53 am

I don't think that protected airspace drove airspeed. Probably the opposite.
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jschnurr
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Re: Why is the max speed for a hold faster when climbing?

#6 Post by jschnurr » Sun Dec 10, 2017 12:59 pm

Has anyone actually been given a hold while climbing? Most holds are before approaches when the aircraft is descending. My guess why the holding speed is faster for climbing turbojets is so they have the option to reach an efficient altitude faster (I realize that "holding" and "efficient" should never be in the same sentence...)
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Re: Why is the max speed for a hold faster when climbing?

#7 Post by Schooner69A » Sun Dec 10, 2017 6:18 pm

I think Kevenv has it. I haven't looked at the protected airspace for holds for years, but I'm guessing said airspace is much larger when cleared to "Climb in the hold to FL 20000 BPOC"... Or somesuch.
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Re: Why is the max speed for a hold faster when climbing?

#8 Post by photofly » Sun Dec 10, 2017 6:52 pm

This article touches on the question (on page 1, at the top of the second column)
http://www.terps.com/ifrr/dec95.pdf

If you want to know more, you'll find Wally Roberts on PPRuNe - you can ask him there.
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Re: Why is the max speed for a hold faster when climbing?

#9 Post by dialdriver » Sun Dec 10, 2017 6:59 pm

Would the best rate of climb speed be a factor? I think it's closer to 300 kts for a medium jet.
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Re: Why is the max speed for a hold faster when climbing?

#10 Post by photofly » Sun Dec 10, 2017 7:08 pm

Reading Wally's article, it's reads as though it was just to make it easier for ATC to know what airspace they have to protect: since the speeds and protected areas vary with altitude, if the altitude is varying it's simpler just to protect to the highest speed for any aircraft, and 310 knots was the fastest speed for which holds were designed, used by some 1960's era military jets.
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