Descent planning questions
- Thread starter Mavmb
- Start date
BEEF SUPREME
Well-Known Member
Are you asking a question?
bucksmith
Did you lock the doors?
Did you ask the box before you asked us?? Lucky enough to have a banana, that's even better!
bucksmith
Did you lock the doors?
But seriously, how miles are you going a minute? The easy part is you gave a fpm. A little more math if you need to start down now and want to know your fpm. (But not much more)
bucksmith
Did you lock the doors?
I always add a few for the push over.
Screaming_Emu
Well-Known Member
I flew with a dumbass that wanted me to start down in V/S just befor path started down. "It's so much smoother."
1) Way more work.
2) We fly boxes.
francis03
Well-Known Member
Vertical Direct-To?
JeppUpdater
Well-Known Member
Don't overthink it:
Altitude AGL in thousands x 3 = distance to start down
Groundspeed / 2 = target vertical speed
Cruising FL390 going to a 1000' MSL airport, 38000 AGL...38x3 = 114 nm start down
Doing 480 knots... 480 / 2 = 240, so do 2400 FPM initially down
Check it on the way down and adjust the VS for groundspeed changes or altitude getting off slightly. I'll usually start down a mile early to let the plane get established.
Or yeah, it's 2016 and laziness is available... "VNAV D->", confirm, then "Activate VNAV D->" (I mental math check this because I've seen way too many FMSs do stupid stuff).
Altitude AGL in thousands x 3 = distance to start down
Groundspeed / 2 = target vertical speed
Cruising FL390 going to a 1000' MSL airport, 38000 AGL...38x3 = 114 nm start down
Doing 480 knots... 480 / 2 = 240, so do 2400 FPM initially down
Check it on the way down and adjust the VS for groundspeed changes or altitude getting off slightly. I'll usually start down a mile early to let the plane get established.
Or yeah, it's 2016 and laziness is available... "VNAV D->", confirm, then "Activate VNAV D->" (I mental math check this because I've seen way too many FMSs do stupid stuff).
gotWXdagain
Polished Member
1500 ft above field elevation by 5 miles out, set a 1500fpm descent and let Betty tell me when to pull the lever back.
Sent from my iPad using Tapatalk Pro
Sent from my iPad using Tapatalk Pro
Maximilian_Jenius
Super User
This all sounds Chinese to me. What is a good book to pick up to learn how to do this stuff?
bucksmith
Did you lock the doors?
MidlifeFlyer
Well-Known Member
Just to a google search for aviation rules of thumb or aviation math. The basics of descent planning are "simple" algebra and geometry.
Rate of descent = Ft to lose/distance X groundspeed/60
Is the basic formula. You can take those numbers from the original post, plug them in and get the answer. Like any other formula, it can be moved around to use what you do know to calculate what you don't.
The other piece is using the "standard" 3 degree approach descent we've been taught since student days and especially in basic instrument training.
But if algebra is Chinese to you, there are a bunch of rules of thumb that are based on it. Most are calculating practical things, like, when should I start down at my desired descent rate or what vertical speed do I need to meet that crossing restriction.
A few mentioned altitude to lose / 3 and GS X 5 (or GS / 2 and add a 0, which is the same thing) . Both are just applying the 3 degree descent rate to the formula in a way that shortcuts the calculations.
Others mentioned figuring out miles per minute. That's just the GS/60 part.
Last edited:
NovemberEcho
Dergs favorite member
Any time I'm thinking of taking up flight lessons again I stumble across a thread like this, remember I failed high school algebra twice, and put my wallet back in my pocket.
Maximilian_Jenius
Super User
True, I get it, see it now. But here's my main issue. When it comes to math, I'm almost dyslexic. And 100% visual, vs. mental. I have to see it with my eyes to get it, or to be able to tackle the problem.
In an interview you can't/shouldn't pull out your Galaxy phone, when they ask: "You're at FL350, and ATC needs you to cross DOGGS at 15,000. When do you start down? You probably also couldn't/shouldn't say. "Autopilot off, FLCH, green arc to DOGGS. Or another scenario when you're in the jet, you don't want to break out paper and a pen. Or bring out the E6B or the Galaxy 7.
So how in my case can I learn to quickly and mentally see the math in my head that FL350 -15,000= 20,000 ft. to lose. And 20x3= 60 So you would start your descent 60 miles out?
Pretty sure that I'm not the only visual learner here.