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Climb Gradient Requirements

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Climb Gradient Requirements

Old 2nd Feb 2012, 13:53
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Climb Gradient Requirements

Hi Folks,

I'm really curious about the calculation of the possible climb gradient on departure. This question came up the other day when we departed from Chicago o'Hare Airport. In the departure plate it says the o'hare departure needs you to be in 5NM at 3000ft and in 8NM at 5000ft. How can you calculate if you are able to do it if you fly an e.g. A340-600 or a B747 or a A320 etc. When can you accept this departure or when is it better to refuse it. I would really appreciate any rule of thumb or detailed formula.

Thanks
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Old 2nd Feb 2012, 13:57
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Whats up with your name?
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Old 2nd Feb 2012, 16:09
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They let you in?

Yeh, I'm surprised you got in, even more so that you got out.
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Old 2nd Feb 2012, 16:23
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That's a pig of a question.
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Old 2nd Feb 2012, 17:03
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Just like the name, you can't do it. Climb gradient info isn't part of the performance manuals.
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Old 2nd Feb 2012, 18:22
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H-Pork:

I'm really curious about the calculation of the possible climb gradient on departure. This question came up the other day when we departed from Chicago o'Hare Airport. In the departure plate it says the o'hare departure needs you to be in 5NM at 3000ft and in 8NM at 5000ft. How can you calculate if you are able to do it if you fly an e.g. A340-600 or a B747 or a A320 etc. When can you accept this departure or when is it better to refuse it. I would really appreciate any rule of thumb or detailed formula.
I don't find that on my Jepp charts.
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Old 2nd Feb 2012, 19:30
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Hi HPork,

I do see the requirment on the plate, basically comes down to a 600 ft/nm climb, which at typical speeds is around 1800 ft/pm, just go full blast and that should work out even on the 74 just don't accelerate at 3000ft

Alternatively you can input ORD on your fix page, draw a 5 mile ring and input the intersection on your legs page with a 3000 ft or above constriction, if it starts blaring inform ATC.
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Old 2nd Feb 2012, 21:35
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ft
 
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Whip out your trusty E6B/CR-3/CR-2, set the planned ground speed at the speed index and read the required FPM above the required feet per nm.

Theory: If you are doing the set GS, you'll have the GS in nm per minute above 10 on the inner scale. Multiply nm per minute by feet per nm, i e read above the feet per nm rather than above 10, and you get the fpm.

Cheers,
Fred
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Old 2nd Feb 2012, 22:44
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There is only one SID; it's a vector SID:

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Old 3rd Feb 2012, 00:31
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The Douglas/Boeing 717 FMS will make the calculations for you, once final weights have been entered, based on internal performance data, and entered weather/wind data.

If unable to comply, the FMS will annunciation "Alt error at XXXXX". Additionally, if actual performance isn't as expected, it'll produce the aforementioned error.

The flip side of this, is for example the SIDs off RWY29 at YPDN (Darwin) where there is a 3000 requirement at NASUX, some 9.5NM from the upwind threshold. It's quite common to have an ALT ERROR AT NASUX, in the early climb out, as the aircraft accelerates & is reconfigured. Reality is that the limit is easily achieved in this type, even at MAUW on a hot day, with full flex power (assuming 21k engines).
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Old 4th Feb 2012, 03:02
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Gradient

HP, here goes : 5NM @ 3000 ft AGL = a grad of 600 FPM or 5.67 degrees
8NM @ 4000 ft AGL = a grad of 500 FPM or 4.72 degrees

The way to calculate is to divide the height by the distance to get the gradient.
Then divide the gradient by 6076 (ft in 1 NM). Then go ARC Sin on a scientific
calc to get the angle in degrees.

EG: 3000/5=600/6076=0.987491 (% grad), arc sin =5.67

Since DME is slant range, we use the SIN (hypotenuse) of the angle.

Always have a scientific calc with you.
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Old 4th Feb 2012, 03:42
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Or you could make a wag and say climb speed is 2.5 MPM so you need at least 2,500 FPM climb which all aircraft can do.
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Old 4th Feb 2012, 09:31
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BTW I think there is only one SID. Hard to refuse it

SERIOUSLY guys why dont you for once listen to someone with sense and knowledge :
Intruder Just like the name, you can't do it. Climb gradient info isn't part of the performance manuals.
just go full blast and that should work out even on the 74 just don't accelerate at 3000ft
REALLY?

Last edited by de facto; 4th Feb 2012 at 09:58.
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Old 4th Feb 2012, 18:21
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ft
 
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If you really can't find the climb gradient in your performance manuals, I have a feeling you may have a hard time complying with certain requirements to show that you can depart without hitting anything.
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Old 5th Feb 2012, 00:11
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FT,

Many of the newer aircraft no longer have this information in their manuals, because they now use AFM DPI (digital perfomance information)

For example, you will (assuming you have paper manuals onboard) see a reference to consult the PEP (perfomance engineers program)

In my company we have the EFB and that is the only source of perf information we have... You wont find any books to look this stuff up in..

This does give us the climb gradient we can achieve for the current conditions both all engine and OEI..
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Old 5th Feb 2012, 18:28
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ft
 
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PT6A,
please send me a post-card from your vacation in the Land of Semantics.

Address:
Fred
Practical Applicability Rd.
RW-127 85 The Real World



Cheers,
Fred
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Old 5th Feb 2012, 18:35
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Ft,

Can't manage the postcard... But here is the extract from the EASA Approved AFM.

TAKEOFF PERFORMANCE Ident.: PERF-TO-00006904.0001001 / 23 NOV 09 EASA APPROVED Criteria: SA

For takeoff performance determination on dry and wet runway, the Performance Engineer's Programs/AFM_OCTO approved FM module at the latest approved revision must be used. Refer to PERF-OCTO Performance Database. CAUTION For takeoff performance on wet runways the takeoff weight must be the lowest of the computed one on dry runways and the computed one on wet runways.
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Old 5th Feb 2012, 20:25
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ft
 
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Point-in-case:

The data is there, as part of the data package. Part of the AFM has moved into a piece of software referenced from the AFM. Doesn't really change anything, except for the fact that it will worry me and other members of the Neo-Luddite Society who believe that someone will, sooner or later (and probably me/sooner, according to member of very high standing Mr. Murphy), end up without precalculated take-off data, batteries, power outlets, phone and paddle in Stercus Creek, WI.

(We maintain that electronic-only data critical to flight is an evil only slightly lesser than that new-fangled reaction engine which is getting all the hoopla nowadays.)

Arguing the form of data when meeting the statement that it "cannot be done as it's not in the perf manual" is semantics. And I want my post card!
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Old 5th Feb 2012, 21:02
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These questions are rhetorical...

So in the above examples... have we not forgot that ORD probably has an elevation, meaning the 3000ft MSL will mean an altitude of 2800ft* ish to climb? (This may be food for thought only for "academics"/calculator-pilots).
*) Did not remember the elevation, but it was 200something.

Another thought... Is the DME adjusted to read ZERO at DER of RWY in use? If the DME reads other than ZERO at DER, how much will that affect the gradient?

And will SLANTrange versus geographical 5 nautical miles be an issue (give large errors in calculation) when we talk about a climb gradient of 10%?

I am pleased to read the rules of thumb regarding calculation of climb gradients. There is a lot of knowledge within this forum, no doubt!

Boeingisgoing:
And by coincidence it works out that a given climbgradient multiplied by 2 is the climb per minute in feet at 200 kts groundspeed.
In this example: 10% X 2 = 2,000 feet per minute at 200 kts groundspeed. And if you are doing 250 kts, add 25% which will be 2,500 feet per minute.
Well, it is an even greater coincidence that any climb gradient in per cent (%) multiplied by the ground speed (GS) in knots will give you the required rate of climb (ft/min). This will be an estimate within limits that will vanish in the effect of i.e. wind.
200x10% = 2000fpm, 180x3,3% (200ft/nm) = 594 (rounded 600fpm)

Back to the O'Hare example, it may be so that the sources for error I am referring to above may be so small that they are negligible, but I think this is the right place to ask such questions. -So being a relatively junior pilot, I dare ask these questions and wait for my head to be chopped off (which happens often at these forums).
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Old 6th Feb 2012, 01:24
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Why not just simplify things.

When you call delivery tell them you are unable 3000' at ORD 5 DME. (Just like the jepp plate says.) This is what a major local airline does (United).

ORD ATC is well aware that a heavy B744 etc. probably won't meet the restriction.

UA accelerates at 800' AGL with CLB thrust at flaps 5. At MTOW on the B744 they will definitely not meet 3000' or above at ORD 5 DME.

LH on the other hand simply accelerates at 3000' with thrust reduction at 1500' on the B744 out of ORD. Of course they never go out anywhere near MTOW on a ORD-FRA flight.
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