How does Center know?

aloft

New Member
Question for the big iron drivers (or really anyone who flies in the flight levels): how does Center know when you want to start your initial descent?
 

Derg

Cap, Roci
Staff member
Well, they generally know that you want to be 30 miles out at 10,000 and 250 to 320 knots.

Or they might know you have a particular crossing restriction as per your arrival and you're getting close to the 3:1 glidepath.

Remember, ATC knows your filed IFR flight plan, your planned airspeed and a little (and I do mean a little) information about the performance of your aircraft.

Speaking of that, my uncle just retired who was a supervisor at Miami Center. They have a madatory age-56 retirement!
 

Eagle

New Member
they also have arrival requirements where ATC needs you at an alt. that is when you get.

Cross XYZ at 120.

There is a formula (escapes me right now) talks about how to figure when to start your desent to be at the crossing alt on time. I do it the old math way. xxxFPM/number of feet needed...
 

Cheechako

Well-Known Member
Sometimes they "forget" about you and you have to ask for lower. This happens many times into smaller airports without published arrivals.

Many time they'll say "descend pilot's discretion" to a lower altitude giving the pilots the option of when to start down.
 

Derg

Cap, Roci
Staff member
I always like the "Descend and mainain flight level 24,000, at pilots discretion to maintain 12,000, cross 40 miles west of Wasatch at 15,000, Salt Lake altimeter 30.32"

Pretty easy with an FMS and autopilot. Put FL 240 in the cruise page, put 12,000 in the altitude window of the autopilot and type "TCH/-40" in the DIR/INTC page, and then "/120" in the altitude restriction next to "TCH01".
 

Cheechako

Well-Known Member
Hah! That reminds me. . . there I was. . .

Our FMS blanked out in PHX so we had to fly to SLC "green needles" (the old VOR-VOR method!). We got the "cross 40 south of Wasatch at 12000 feet, 250 knots." Oh great, I'm actually going to have to think about this! But then he gave us discretion to 11000. Phwew!
 

jdflight

Well-Known Member
The "old" VOR-VOR method? That and ADF are the only methods I can do, and having just reached the end of stage 1, I wouldn't want to rely on me!
 

ready2fly

Well-Known Member
Here here, jdflight! I'm in the same boat. I'm just starting Stage II in the Jepp Syllabus! I'm with ya bro!
 

jdflight

Well-Known Member
I failed my stage I yesterday. Pissed me off to no end. Our chief pilot did it, and everyone dreads doing rides with him because of the way he thinks. He's extremely technical, and I basically failed it because, even though I was within PTS, I was chasing the altimeter within 100 feet of my assigned and couldn't get it trimmed. While he can't fail me on that, he's really not interested in seeing me repeat what he could fail me on, which was a botched NDB procedure turn. I forgot which heading I started on and therefore couldn't find the reciprocal when I came back around. Legitimate, but he knows I can do it and I knew what went wrong, so he's not even sure we're going to do it again on the retake today. I realize that failing a stage check isn't that big a deal, but for me, personally, it's huge.
 

ready2fly

Well-Known Member
Don't sweat it. I take those kinds of things personally too. You'll do fine. Just look at it as a chance to show off what you know.

If it helps - TALK your way through it ... out loud.... so that he can see you know what you are doing.

FWIW - I have JUST gotten the gist of trimming the plane. So, you're not alone.
 

jdflight

Well-Known Member
What kills me is that I've never had much trouble trimming the airplane. But that damn Frasca sim, I just can't get her trimmed right!
 

drumminpilot

Well-Known Member
hahaha...... The words "trim" and "Frasca" go together like the words "military" and "intelligence"
I swear that damn trim wheel is just there to taunt us.
 

drumminpilot

Well-Known Member
lol...... no insult...... I tried to think of something else, but that was the cleanest thing I could think of.....
 

chunk75

Well-Known Member
[ QUOTE ]


There is a formula (escapes me right now) talks about how to figure when to start your desent to be at the crossing alt on time. I do it the old math way. xxxFPM/number of feet needed...


[/ QUOTE ]

How about this one...to quote John Deakin again:

"One common method of tracking this is to knock off the three trailing digits of the altitude above the airport (for a sea-level airport, 45,000 becomes 45), and multiply that by three (getting 135) for the approximate correct distance from the airport to start down.

(Note this gives "air miles," or the distance to fly. If you're on a vector for an ILS landing in the opposite direction, that usually adds about 30 air miles to the descent.)"
 

Soonermurph

New Member
Re: Decent planning formula

Use the 3:1 rule for distance (three miles for every thousand feet needed to decend). Also, use the following for decent rate: take the groundspeed (example 150 kts.) add a 0 to the end (1500 kts), then divide by 2 (750 fps). There you go.
 

Eagle

New Member
Re: Decent planning formula

[ QUOTE ]
Use the 3:1 rule for distance (three miles for every thousand feet needed to decend). Also, use the following for decent rate: take the groundspeed (example 150 kts.) add a 0 to the end (1500 kts), then divide by 2 (750 fps). There you go.

[/ QUOTE ]

Not following you on this.

at 300kts, it is 1500fpm ,are you saying if I need to loose 15000ft, at 45 miles out drop at 1500fpm? I'll try it tomorrow and report back
 

ananoman

New Member
Re: Decent planning formula

A three degree glideslope is 300' per NM. Divide altitude to loose by 300. To get required descent rate multiply ground speed by 5. You should do the same thing when flying an ILS to get your target descent rate.
 
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