This whole ODP-200FT./NM. thing

Dmitri Scheidel

Dmitri Scheidel

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Hello,
First off, I'm not an IFR pilot, I'm still working on my PPL. But I still want to learn the world of IFR so I'm ready for IFR training. I'm watching a workshop on IFR DP's, and the guy started with a thing called an ODP. (Cross the DER >35' feet with a climb gradient of at least 200FT/nm. if that's correct).

I'm stubborn and like to work things out by hand, and I'm trying to figure out this whole 200FT./nm. thing. If I climb out at 70Kts., how can I calculate my expected VS to be able to match the 200FT/nm requirement? My white board is full with marks and calculations, but I can not figure it out.
Thanks!
 
At 60kts, you travel 1NM in 1 minute, so 200ft/nm would simply be 200 FPM.

To calculate your required vertical speed, just figure out the factor between your speed and 60 knots. If you're doing 120 kts, that's a factor of 2. So your necessary VS would be 2 x 200, or 400 FPM.

At 70 knots, that factor is 1.17 (70/60), so your necessary VS would be 200 * 1.17, or 234 FPM.
 
BTW, for the even simple math challenged, the FAA is kind enough to to provide a conversion chart in the terminal procedures publication.
RateTable.jpeg
 
You can use an E6B as well. I've used the one on my watch on occasion. Put your GS at the top of the arrow. Go to ft / nm requirement on the inside scale and your required ft / min will read opposite it on the outside scale.
 
OverTQ said:
At 60kts, you travel 1NM in 1 minute, so 200ft/nm would simply be 200 FPM.

To calculate your required vertical speed, just figure out the factor between your speed and 60 knots. If you're doing 120 kts, that's a factor of 2. So your necessary VS would be 2 x 200, or 400 FPM.

At 70 knots, that factor is 1.17 (70/60), so your necessary VS would be 200 * 1.17, or 234 FPM.
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Good way to calculate it. But be sure to use Ground Speed, not your TAS.
 
RotorDude said:
Good way to calculate it. But be sure to use Ground Speed, not your TAS.
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I'm sure people forget that so important point. Whatever calculation you use, it's GS not IAS.

Of course, for planning purposes (as in, "can I do this?") GS is going to be a prediction and can very easily change during the climb, especially in areas where it's going to be important (i.e., winds ebb, flow, and funnel in areas where terrain is the reason). So, you might well be stuck with using an approximation with a nice buffer.
 
OverTQ said:
At 60kts, you travel 1NM in 1 minute, so 200ft/nm would simply be 200 FPM.

To calculate your required vertical speed, just figure out the factor between your speed and 60 knots. If you're doing 120 kts, that's a factor of 2. So your necessary VS would be 2 x 200, or 400 FPM.

At 70 knots, that factor is 1.17 (70/60), so your necessary VS would be 200 * 1.17, or 234 FPM.
Click to expand...
And, without the factor, it's climb required in FPM X GS/60. The factor is GS/60.
 
midlifeflyer said:
I'm sure people forget that so important point. Whatever calculation you use, it's GS not IAS.

Of course, for planning purposes (as in, "can I do this?") GS is going to be a prediction and can very easily change during the climb, especially in areas where it's going to be important (i.e., winds ebb, flow, and funnel in areas where terrain is the reason). So, you might well be stuck with using an approximation with a nice buffer.
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Fer sure use GS and always keep in the back of your head the red flag of tailwinds.
 
RotorDude said:
Good way to calculate it. But be sure to use Ground Speed, not your TAS.
Click to expand...
Worse yet, I've seen pilots use INDICATED AIRSPEED instead of ground speed...ugly at 12,000 ft.

Another way to look at the problem, though, is that 200 ft/mile is 3.3%; 100 ft/min is almost exactly 1 knot.

3.3% of 70 knots is 2.31 knots, or 231 ft/minute.

Granted, you can probably fly 234 ft/min from the earlier calculation accurately enough that my way has too much error, but I can't. ;)
 
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Dmitri Scheidel said:
Thanks so much for that!!!! I'm still discovering more and more things in the AFD.
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This one is not the AFD (now known as the Chart Supplement).

This chart is in another soft cover book (assuming we're using paper) called the Terminal Procedures Publication. It's the one that includes instrument approach charts and other instrument procedure information.

Not much reason to delve into it at this stage of the game, other than knowing there are procedures, charts, rules, regulations and other procedural material applicable to the IFR world beyond what you are learning at the student-to-private stage. You have plenty to learn right now.
 
Velocity173 said:
You can use an E6B as well. I've used the one on my watch on occasion. Put your GS at the top of the arrow. Go to ft / nm requirement on the inside scale and your required ft / min will read opposite it on the outside scale.
Click to expand...

Yeah. Takes about 3 seconds. This is one of the things that an E6B shines at
 
luvflyin said:
Yeah. Takes about 3 seconds. This is one of the things that an E6B shines at
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Takes more than 3 seconds to find my manual E6B, especially since it sits in a box at home waiting to be used for a ground session on flight planning :D
 
That chart is also in the figures book for the writtens... But you'll have to dig in the table of contents to find it. Interesting all the stuff that's in the new ones, actually. And pretty colors too. Ha.
 
What happened to doing math in one's head?
 
EdFred said:
What happened to doing math in one's head?
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I had a similar thought. It's not terribly hard math.

FPM = FPNM * GS / 60.

If I climb at 75 (Warrior or 172), the factor is 1.25. If I climb at 90 (182 or Archer), it's 1.5. Raise the speed by 2% per thousand feet DA if applicable (most of the local airports are at or very near sea level), and subtract the headwind.

To the OP, VERY few of the ODPs around here use the minimum climb. Too much terrain. For instance, all of the Napa departures off 36L/R (all the SIDs plus the ODP) require climb rates of nearly 400 ft/nm. Easily done in most aircraft, but you may need a Vy climb. At 90 knots in a 172, that's 600 FPM, and it's not going to do it at that speed (at least, not loaded to max) in no wind. You'll get the necessary 500 FPM at 75.

BUT, if the winds are blowing over the mountains to the airport, descending air can ruin your whole day. Use a different runway or scrub if the good ones all have tailwinds.

It's a big deal because the terrain can easily be in the clouds.

Fortunately, it never gets really hot at Napa, though the weather very definitely does get crappy.
 
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RussR said:
It's also available as one of the document downloads in ForeFlight.
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For this you download the Digital Terminal Procedures Supplement. The table is page 19 of 19.
 
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