VDP and Enroute Decent
12-03-2006 | 11:55 AM
#1
Thread Starter
Line Holder
Joined: Nov 2006
Posts: 91
Likes: 0
From: trying to survive
VDP and Enroute Decent
I've only been flight instructing for a short time now, but I haven't had much expereince with VDP's or decent planning. I've heard people talk about things like the 6/3 rule and whatnot but they never elaborate on exactly what that means. I'm wondering two things, and so I understand I'll use specific situations: How would I calulate a VDP for both time and distance if the TDZ elevation is 750 feet? Second, if I'm at FL240 and have to get down to 10,000 feet, how do I know when to start the decent and what decent rate to use? How about for a 3 degree glide slope? I know this stuff is probably common sense for many of you but I simply have not really had to work with it much.
Also, does anyone know what brown diamonds along an airway means on a jepp chart?
Also, does anyone know what brown diamonds along an airway means on a jepp chart?
Last edited by beech2jet; 12-03-2006 at 01:47 PM.
12-03-2006 | 01:24 PM
#2
Gets Weekends Off
Joined: Feb 2006
Posts: 441
Likes: 0
From: 747RJ
If you have a GPS equipped airplane for a 3 degree descent: 3:1 rule. OK FL240 to descend to 10000 feet. You have 14000 feet to lose (+/- altimeter change muy importante) Divide alt to lose by 1000 = 14. Now take 14*3=42. You need to start down 42 nm out from your fix. To approximate a 3 degree glide path, use 1/2 your groundspeed * 10. So a 420 KTS G/S means 2100 fpm.
The VDP is based on the same principle. Say you need 1 1/2 SM to land. Using the 3:1 rule, you need 300'AGL for every 1SM of visibility. So for a 3 degree approach to landing you need to see the runway at 450'AGL in our example. Add 450 to 750, and your VDP will be at 1200 MSL.
The VDP is based on the same principle. Say you need 1 1/2 SM to land. Using the 3:1 rule, you need 300'AGL for every 1SM of visibility. So for a 3 degree approach to landing you need to see the runway at 450'AGL in our example. Add 450 to 750, and your VDP will be at 1200 MSL.
12-03-2006 | 03:12 PM
#3
Gets Weekends Off
Joined: May 2006
Posts: 187
Likes: 0
never seen a VDP caluclated that way before....If its for Time, take 10% of your HAT. say your HAT is 400'. Thats 40 Seconds. If your Time for the approach is 3:40...you will arrive at your VDP at 3 minutes. (40 seconds priopr to the missed approach point)
If its based on DME, devide your HAT by 300. Say your HAT is 300'. You're doing a LOC/DME approach. Missed is at 1.5 DME. 300/300=1. Add 1 mile to your missed DME to get your VDP....2.5DME you will be at the VDP(1 mile prior to the Missed approach point). You will need to either add or subract the DME figure you get depending on whether the navaid you are using is on the field or off the field. If it is on the field, such as in my example, you add to your Missed DME to get the VDP if its off the field, you subtract it.
If its based on DME, devide your HAT by 300. Say your HAT is 300'. You're doing a LOC/DME approach. Missed is at 1.5 DME. 300/300=1. Add 1 mile to your missed DME to get your VDP....2.5DME you will be at the VDP(1 mile prior to the Missed approach point). You will need to either add or subract the DME figure you get depending on whether the navaid you are using is on the field or off the field. If it is on the field, such as in my example, you add to your Missed DME to get the VDP if its off the field, you subtract it.
12-03-2006 | 03:34 PM
#4
Gets Weekends Off
Joined: Nov 2005
Posts: 1,624
Likes: 0
From: AA A320
most people just divide the HAT by 300 (though the real number is 318 I think, but hey its just an estimate).
You could do the same thing to figure out an enroute descent for a 3 degree glideslope.. however crossing clearances are not always issued on the premise of a 3 degree glideslope.
You have to figure out how many miles per minute your are going (GS),
then how many miles til the fix,
that calculation will show how many minutes til crossing fix,
then divide altitude to lose by time to fix to find FPM to cross fix at assigned altitude.
You could do the same thing to figure out an enroute descent for a 3 degree glideslope.. however crossing clearances are not always issued on the premise of a 3 degree glideslope.
You have to figure out how many miles per minute your are going (GS),
then how many miles til the fix,
that calculation will show how many minutes til crossing fix,
then divide altitude to lose by time to fix to find FPM to cross fix at assigned altitude.
Last edited by KiloAlpha; 12-03-2006 at 03:40 PM.
12-03-2006 | 03:35 PM
#5
Che Guevara
Joined: Aug 2005
Posts: 6,408
Likes: 0
That seems WAY to hard compared to what it has to be. 6*groundspeed, 3*altitude.
If you are at 24k and want to get down to 10k. You have 14k to lose. Just take 3*14=42nm. Simple. The GS is for how many fpm you should be descending.
You can use it for approaches or descents becaues it's all based on 3 degrees which is what your plates are for.
If you are at 24k and want to get down to 10k. You have 14k to lose. Just take 3*14=42nm. Simple. The GS is for how many fpm you should be descending.
You can use it for approaches or descents becaues it's all based on 3 degrees which is what your plates are for.
