Topic Author
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Climb Gradient On SIDs

Tue Jun 18, 2002 8:11 pm

Hi everyone,

While going through some SIDs charts today I noticed that there are different climb gradients at different parts of the SIDs. What does this 'climb gradient' mean?


Boeing747 万岁!
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RE: Climb Gradient On SIDs

Tue Jun 18, 2002 8:52 pm

"Normal" SID's are designed in such a way that a climb gradient of 3,3 % (201 ft climb per nautical mile of distance) will keep you clear of all obstacles in the departure path.
Sometimes, in mountainous areas or for ATC-reasons, a bigger climb is necessary. If the required climb gradient is bigger then 3,3 %, this will be said in the SID procedure itself. For instance: 5,4 % climb required until passing a certain point. In this case if you were climbing at a groundspeed of 160 knots you would need a climb ratio of about 864 ft/min. (160 *5,4 (rule of thumb))

hope this helps!


RE: Climb Gradient On SIDs

Tue Jun 18, 2002 9:33 pm

Here's an example of what Erarmus said about Departure Procedures "DPs" (I guess that we really ought to them by their correct name - it was changed a while back.) with non-standard TERPS climb gradients...

Departing IFR out of Aspen, CO (KASE) on RW33 via the Aspen Two Departure requires a climb gradient of 950’ /NM to 12,000’ MSL. This departure is basically a slight right turn after takeoff followed by a straight out climb. The Lindz Four Departure is somewhat more manageable with a required climb gradient of “just” 460’/NM to 14,000’ MSL. However, this procedure is pretty complex, involving the interception of an offset back course LDA then the interception of a radial off of the DBL VOR. The published Takeoff & Obstacle DP is similar to the Lindz Four Departure. As far as departing from RW15, forget it. Only the Space Shuttle would have the climb gradient necessary.

Topic Author
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RE: Climb Gradient On SIDs

Sat Jun 22, 2002 11:55 pm

Thanks people!  Smile Now I understand.
Boeing747 万岁!
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RE: Climb Gradient On SIDs

Tue Jun 25, 2002 1:50 am

Does anyone have any maximum climb gradients for today's airliners, I presume it varies with Take off weight

RE: Climb Gradient On SIDs

Tue Jun 25, 2002 8:11 am

Climb gradient for transport airplanes certificated in USA are subject to US/FAR 25... the most "critical" gradient (or hardest to achieve) is the "second segment climb gradient"... which is assumed to start at gear retraction (that is the end of the first segment), and completed at a height "not less" than 400 feet above the reference point...
The configuration for the second segment for all airplanes is as follows -
* gear completely retracted,
* flaps at the takeoff position,
* one critical engine "out" (outboard engine on 4 engine aircraft),
* other engines (remaining operating at maximum T/O thrust),
No change of configuration permitted during the second segment...
The gradient of climb required to be achieved shall be no less than -
* 2.4% gradient for 2 engine airplanes, i.e. a B-767,
* 2.7% gradient for 3 engine airplanes, i.e. a MD-11,
* 3.0% gradient for 4 engine airplanes, i.e. a B-747...
The second segment gradient is often the limiting factor for departures at high elevation airports, and high temperature, we say "climb limited"...
In order to achieve a better second segment, some airplanes can select a T/O flaps position which favors the climb, i.e. the 747 can take off with a choice of 20 flaps or 10 flaps... using 20 flaps favors "runway limit weight" but is detrimental to the second segment climb limit weight... using 10 flaps favors the "second segment climb weight" but requires a longer runway...
Hope this gives you an idea about the subject... XXXX10...
(s) Skipper
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RE: Climb Gradient On SIDs

Tue Jul 02, 2002 12:18 am

Hey Skipper, I was wondering if outside of the Airport Designers and engineers, do airline pilots deal with all the details of Part 25 and the associated part 77 surface? Or is it just good to know?
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RE: Climb Gradient On SIDs

Wed Jul 03, 2002 11:49 am

Basically, from my point of view, the most important thing regarding the minimum climb gradient on a SID is that whether a twin engine aircraft can acheive the minimum climb gradient with one engine inoperative.

Should you lose an engine on departure, then should you continue with the SID , you want to be able to climb "Over that mountain, which you cant see due to cloud" in assymetric configuration.
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RE: Climb Gradient On SIDs

Wed Jul 03, 2002 12:03 pm

Runway Analysis will tell you the maximum weight you can use for a particular runwayans achieve the second segment climb gradient with a nengine innoperative at V1.

The climb gradient on SIDS arent even looked at if you have RA.

The climb gradient in Ft per NM isn't even a relavant number unless you dig into the performance charts.

Big plus for RA  Big thumbs up

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RE: Climb Gradient On SIDs

Thu Jul 04, 2002 12:47 am

I concur with the above, but would add that many airports have a Jepp 10-7 page which is a specific single engine procedure that may be required in certain 121 ops, that differs from the SID.

Posted by TOPgun under the Violating the SID/STAR Procedures:

RE: Essential power.
It's quite obvious to me that you have never had an instument ground school.

A SID is designed to give you ground clearance provided you can follow three simple things:

1: You keep a 200'/nm climb.
2: You can cross the threshold at least 35' AAE and,
3: You will be at 400' AAE before comencing your turn.

IF you can't keep those, you cannot accept the SID. Which doesn't mean you cannot depart.

As for the STAR they do the same basic thing as a SID but it leads you to the airport instead.

My response to topgun:
Ref AIM 5-2-3
1. "A SID is an ATC coded departure procedure which has been established at certain airports to simplify clearance delivery procedures."
2. Per the pilot/Controller GLossary: "...STARs provide transition from the enroute structure to anouter fix or an instrument approach fix/arrival waypoint in the terminal area.

In short, the concept of ground clearance for a SID is secondary. If it were primary, every airport would have them, as opposed to class B and most C (some D, yeah yeah.)
Secondarily, many SIDs and STARS distinguish b/t Turboprops and Turbojets, as assigning a turboprop to a turbojet departure or vice versa would clog the system and defeat the purpose.

RE: Climb Gradient On SIDs

Thu Jul 04, 2002 1:12 am

Let me add my 2 cents...

For you airline guys, Airport Analysis will have a special departure procedure, if the required climb gradient is too steep, that will give a route that will guarantee obstacle clearance. Even though the Takeoff & Obstacle DP on the back of the Jepp says to climb straight out or make a left or right turn, the Special DP might be an opposite turn. Airport Analysis is specific to each aircraft and takes into account a multitude of factors, like single engine service ceiling, etc.

For us non-airline types, we’ve got to pretty much fend for ourselves when operating at airports whose departure procedures require something other that the standard TERPS gradients. We usually have no choice but to comply with the published SID or Takeoff & Obstacle Procedure. They can be quite complex and convoluted, but it is imperative that they be flown precisely if you want to keep from putting your nose into the dirt when departing these airports under IFR conditions. Typically, our only option is to reduce our weight until we are light enough to meet the published minimum climb gradient.

For those of us operating in the U.S., Canada, Mexico, and (I believe) Chile are fortunate, TERPS takes into account the loss of performance as the result of an engine failure when developing the departure procedures. As far as the rest of the world goes, ICAO does not consider engine failure or any other aircraft emergency after V1 in the construction of departure procedures. Again, you international airline guys have Airport Analysis to bail you out, the rest of us have to work it out for ourselves. But we have help too. There are a couple of takeoff performance calculators on the market that have aircraft specific programing that take the sweat out of working the various performance calculations.


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