ATC Crossing Restriction

[skyhigh600]

Say you are at 16,000ft and you hear:
"N45678 cross OHBOY at maintain 6000".

Now say you are pretty far away from OHBOY. Could you start your descent to 6000' now and arrive at 6000' before reaching OHBOY, or are you required to time the descent such that you reach 6000' at the same time you cross OHBOY??

Secondly, how does this differ (if at all) from:
"N45678" cross OHBOY at 6000" ?

Or would you only hear this given with a descent instruction like:
"N45678 descend and maintain 3000, cross OHBOY at 6000".

How would you plan/execute the descent as given in the last ATC instruction???

Thanks so much!

[PeanuckleCRJ]

Originally Posted by skyhigh600

Say you are at 16,000ft and you hear:
"N45678 cross OHBOY at maintain 6000".

Now say you are pretty far away from OHBOY. Could you start your descent to 6000' now and arrive at 6000' before reaching OHBOY

yep!

Originally Posted by skyhigh600

Secondly, how does this differ (if at all) from:
"N45678" cross OHBOY at 6000" ?

Yoda says, "same thing, is it."

Originally Posted by skyhigh600

Or would you only hear this given with a descent instruction like:
"N45678 descend and maintain 3000, cross OHBOY at 6000".

How would you plan/execute the descent as given in the last ATC instruction???

On this one, descend like you would to normally cross OHBOY at 6000, and, if you were at an altered descent rate (I typically go for an idle descent), resume your normal descent rate after respecting the crossing restriction. When told to descend and maintain an altitude, ATC expects about a 1000 foot per minute descent at a minimum.

[mikecweb]

Also just to give you some ideas based on that restriction.
You'd probably wanna stay up as much as possible. You are above 10k so your speed isn't restricted so you don't exactly wanna rush down to 6,000 and slow up a bunch. Further more we would stay at 16k even longer because we can stay at 350 above 14k(aircraft limitation - Lear 35).
Freight dawgin it we'd probably start our descent at 15ish miles from OHBOY. If no spoilers probably around 25-30 miles to allow for the speed reduction.

[skyhigh600]

Thanks!

One more addition to the question, say you are cruising along at 300 kts...

ATC: "N45678 descent and maintain 3000, cross OHBOY at 6000 and 200 knots"

When would you start slowing to meet the speed restriction? Is the speed restriction still in effect AFTER crossing OHBOY (through 6000 descending 3000)?

Also, am I correct in that once you are cleared for a visual approach any speed restriction previously given no longer is in effect? What about on an ILS or other instrument approach?

thanks again

[mikecweb]

Originally Posted by skyhigh600

Thanks!

One more addition to the question, say you are cruising along at 300 kts...

ATC: "N45678 descent and maintain 3000, cross OHBOY at 6000 and 200 knots"

When would you start slowing to meet the speed restriction? Is the speed restriction still in effect AFTER crossing OHBOY (through 6000 descending 3000)?

Also, am I correct in that once you are cleared for a visual approach any speed restriction previously given no longer is in effect? What about on an ILS or other instrument approach?

thanks again

In general unless you are told to "Resume normal speed" you are held to the previous speed restriction. Obviously on an approach you don't have to maintain 200kts.

[fishrichard]

My rule of thumb for descents is this..The good ole three-to-one,16000-6000=10000, so take 10 multiply by3= 30. So 30 miles out of ohboy is when I'd start my decsent. BUt how fast would you'd desend? Say your ground speed is 400 kts. Just half any ground speed, in this case 2000 fpm outside of ohboy would allow you to make the restriction. It sounds time consuming, but it comes pretty naturally after a few times.

[skyhigh600]

Originally Posted by mikecweb

In general unless you are told to "Resume normal speed" you are held to the previous speed restriction. Obviously on an approach you don't have to maintain 200kts.

Thanks! Makes sense.

However if ATC said "...cross OHBOY at 6000 and 200kts" is the speed restriction in effect immediately or does it just become effective after crossing OHBOY?

Lastly, I have heard over frequency ATC give this instruction:
"N12345, cross 15 miles southeast of XYZ vor, at maintain 6000"

I'm guessing this is used when an aircraft is not on an airway proceeding direct to a VOR? Or is this given even if the a/c is on an airway but ATC needs you to cross some point along the airway (15mi southeast of the vor) that is not an intersection?

thanks again!

[awacs94]

Originally Posted by skyhigh600

Thanks! Makes sense.

However if ATC said "...cross OHBOY at 6000 and 200kts" is the speed restriction in effect immediately or does it just become effective after crossing OHBOY?

Lastly, I have heard over frequency ATC give this instruction:
"N12345, cross 15 miles southeast of XYZ vor, at maintain 6000"

I'm guessing this is used when an aircraft is not on an airway proceeding direct to a VOR? Or is this given even if the a/c is on an airway but ATC needs you to cross some point along the airway (15mi southeast of the vor) that is not an intersection?

thanks again!

That speed restriction refers to when your are at OHBOY. ATC wants you to cross OHBOY AT 200 kts. As long as you were at 200 KTS at OHBOY you have complied with the clearance.