SID Climb Gradient : "Minimum or Average"

[Ear Muffs]

Guys,

Quick question regarding DUBAI 30R ANVIX 3F Departure.

Chart says 5% to 4,000'

Is this a Minimum Climb Gradient or an Average?

EG:

Minimum : Cannot go below the 5% until reaching 4,000' even during the clean up phase

or

Average : Having a greater than 5% for the beginning then cleaning up (Possibly Less than 5% depending on Weight) then greater than 5% once clean.
(Therefore Average for the departure was greater than 5% to 4,000')

I hope this make sense.

A reference would be awesome.

[safelife]

Average, in that segment.
No reference, just logic.

[DaveReidUK]

Apart from anything else, it would be much more difficult (though not impossible) for an ANSP or regulator to monitor instantaneous climb gradients in order to detect infringements.

Far easier to look at the point where you reach 4,000' and then work out what the average gradient must have been.

[president]

Standard SID climb gradients are based on 3.3 pct (2.5 plus 0.8). If due to obstacles (such as the Burj Khalifa) you need more it will be stated on the chart as a min clb gradient up to a certain altitude. The obstacle(s) might be close to the DER or further away or both. If obstacles penetrate the standard OIS the required gradient will be changed. I believe you can not penetrate the given surface as you might hit an obstacle. Especially where you have a high distant obstacle requiring say 5 pct up to 4000 and a low near obstacle requiring a climb gradient of say 4.9 pct up to 2000. By going lower you cannot guarantee obstacle clearance unless you designed the plate yourself. You can therefore climb more than 5 pct and then less as long as you don't penetrate the surface. You can do so by passing 3 nm > 1000ft 6 nm > 2000ft or any other way you want. But you cannot fly level and then climb crazy fast to reach 4000 by the 12nm from the DER (about 5% average). The reference is doc 8168 Part I — Section 3, Chapter 1 paragraph 1.5.5 (It also refers to a nice profile drawing). If the 5 % gradient was due to noise it would be a noise abatement procedure and not a given rate on the plate. So on a normal departure you will climb way steeper until you retract the flaps (and perhaps have a momentary lower gradient) but in my opinion that's totally ok as long as you don't bust the non-standard surface.

[Capn Bloggs]

To back up the president...

Average, in that segment.
No reference, just logic.
Illogical. There could be an obstacle at 3800ft at 5%. If you've done 8% until 2000ft then 1% thereafter (for an "average" of 5%), you could well clobber said obstacle. Just logic. :ok:

[DaveReidUK]

If you've done 8% until 2000ft then 1% thereafter (for an "average" of 5%)

You might want to have another look at your maths.

[Piltdown Man]

Just out of what interest, what sort of plane are we talking about? There are very few jets that can't make 15% up to 10,000' so a paltry 5% up to 4,000' shouldn't be an issue.

[galaxy flyer]

15% to 10,000' OEI, is hard to believe.

[president]

He is talking all engines operating. With OEI you should be on an EFP or be sure you can make the specified gradient on the SID.

[president]

I think the question is more theoretical nature. If you start to accelerate at 800 ft with a V/S of 100ft/min to 250 kts you could temporarily find yourself below the OIS even though your average climb gradient is more than 5 % to 4000. I would say that you have a completely free climb rate as long as you stay above the 5 % surface. Imagine you hit 3950 ft at the DER in you Learjet. I would say it's perfectly safe as long as you climb the remaining 50 in the next 12 NM. On the other hand it's not ok to stay at 50 ft for 11 nm and then do a near vertical climb to hit 4000 by 12 NM (both 5 pct average).

[Capn Bloggs]

You might want to have another look at your maths.
There was never any intention to be accurate. I was merely making the point that just because you did over 5% at some stage and then you do less, it's not the average that counts, it's a minimum of 5% at any point on the SID.

Apart from anything else, it would be much more difficult (though not impossible) for an ANSP or regulator to monitor instantaneous climb gradients in order to detect infringements.
Why would they bother? The company EO procedure may well ignore the SID requirements...

[alphacentauri]

As a flight procedure designer, I assess and design the procedure with an expectation that the gradient required is a minimum until a certain height is reached.

[Airmann]

Don't the charts specifically say minimum? If the SID designers want an average then you place an alt constraint (at or above) and define a waypoint by which you want it.

EDIT: I checked a SID chart out of Dubai it specifically says 'These SIDs require a minimum climb gradient of 5% up to 4000''.

[DaveReidUK]

There was never any intention to be accurate. I was merely making the point that just because you did over 5% at some stage and then you do less, it's not the average that counts, it's a minimum of 5% at any point on the SID.

OK, I hadn't appreciated that accuracy wasn't intended to be part of your response. :O

But even your revised statement isn't necessarily true - your instantaneous climb gradient at any point can be less than 5% and still won't result in you hitting anything solid provided that your flightpath is above the 5% line at every point.

So, for example, if you were minded to maintain 10% to 3000' and then flew the last 1000' at 2%, you would at every point be higher than the 5% average to 4000'.

Or, as President put it more succinctly

You can therefore climb more than 5 pct and then less as long as you don't penetrate the surface

[Capn Bloggs]

Thank you for that.

[aterpster]

president:

He is talking all engines operating. With OEI you should be on an EFP or be sure you can make the specified gradient on the SID.
The latter is an impossible task for the flight crew with OEI. The OEI takeoff flight path "staircases" with a perhaps prolonged level segment. That, and a SIDs constant angle slope over the ground, are incompatible.

[Capn Bloggs]

Galaxy Flyer might be able to hack it. 3rd segment accel = 4000ft!

[president]

president:


The latter is an impossible task for the flight crew with OEI. The OEI takeoff flight path "staircases" with a perhaps prolonged level segment. That, and a SIDs constant angle slope over the ground, are incompatible.

That depends where the engine fails. If you have an engine failure airborne on a normal SID with a 3.3 % requirement you might have the safe choice to stay on the SID and still comply with the required gradient.

[john_tullamarine]

with a 3.3 % requirement you might have the safe choice

A big ask. Unless the sums have been done beforehand, or the weights are very light, the gradient capability mismatch OEI/AEO might put the aircraft in harm's way.

All this should emphasise the need for adequate OEI escape planning ... this stuff usually is quite incompatible with winging it on the fly.

[galaxy flyer]

Bloggs,

I'm trying to understand your post-facetious or insulting? BTW, haven't you seen acceleration heights or altitudes above the FAR 25 1500' AFE?

[Capn Bloggs]

I'm trying to understand your post-facetious or insulting?
I'm thinking the machines you fly could do 5% to 4000ft on one engine (at least sometimes?), that was all. GF. No sinister intent. :)

[galaxy flyer]

Yeah, in many cases, but, like all planes, being at the limit was always a challenge. A Global at the limit isn't much better than any other FAR 25 plane. I just looked about 5% to 4,000' at 20, S.L airport, the limit weight for obstacle is about 83,000#. MTOW is 99,500.

Thanks for the clarification.

[aterpster]

president:

That depends where the engine fails. If you have an engine failure airborne on a normal SID with a 3.3 % requirement you might have the safe choice to stay on the SID and still comply with the required gradient.
True, but irrelevant to performance and engineering. The starting point for computation of the takeoff flight path is an engine failure just above decision speed.

Also, good planning requires a contingency if the engine fails airborne and early into a SID. How do you switch to the preplanned OEI track? Sometimes, that path quickly disappears in mountainous areas. Thus, the reason the U.S. carriers got the FAA to permit the carriers to use a pre-approved carrier-developed departure path instead of using the canned SID. This option is generally limited to airports with challenging terrain.

[president]

with a 3.3 % requirement you might have the safe choice

A big ask. Unless the sums have been done beforehand, or the weights are very light, the gradient capability mismatch OEI/AEO might put the aircraft in harm's way.

All this should emphasise the need for adequate OEI escape planning ... this stuff usually is quite incompatible with winging it on the fly.

I wrote MIGHT. Everything depends on the situation, obviously. And I didn't suggest you should not plan ahead. Just pointed out that it could be an option to continue the SID.

[president]

president:


True, but irrelevant to performance and engineering. The starting point for computation of the takeoff flight path is an engine failure just above decision speed.

Also, good planning requires a contingency if the engine fails airborne and early into a SID. How do you switch to the preplanned OEI track? Sometimes, that path quickly disappears in mountainous areas. Thus, the reason the U.S. carriers got the FAA to permit the carriers to use a pre-approved carrier-developed departure path instead of using the canned SID. This option is generally limited to airports with challenging terrain.

I haven't been suggesting to follow an SID with an engine loss at V1. In fact this discussion wasn't even about engine out performance. What I did say was that with OEI you should be on an approved EFP... OR in some cases continue the SID IF you can make the required gradients. If not you obviously don't.

[president]

I agree. It's an option and that was my only point. I started the sentence by saying you should be on an EFP, so I don't see what the fuzz is about. It's also an option to manoeuvre visually around the objects in VMC. Or fly straight out over the sea and deviate from both the EFP and SID. Or stay at home. I didn't comment on what is clever or easy to do. There are many valid options, and it's our job to choose the best.

In some cases with a late engine failure you would be a fool not to continue the SID. Before you all start... in SOME cases.

[john_tullamarine]

I wrote MIGHT.

Noted. My comment was not intended to criticise you at all, rather, I am always cognisant of posts being read by newchums, hence the clarification.

make decision based upon the sum of your experience

.. but why waste effort and all that experience when it would be far simpler, and a whole sight more valid and useful, to do (or have your operator do) the escape sums before hand ?

What I did say was that with OEI you should be on an approved EFP

Generally, that covers the V1 case. The big problem is no V1 failure, continue SID, noise stops well into the SID but well prior to a safe area height ...

In some cases, the operator will require all departures to be via the escape where the SID is too limiting. In all (ie most occasions) of the remaining cases, the ops engineers SHOULD have done the sums to get you out of trouble with a failure ANYWHERE along the SID flightpath. Unfortunately, this is not the case so often and the Commander is left holding the baby ..

and I'm obviously without doubt above the min gradient well maybe yes just hold at the end of it or pick up vectors

Maybe yes, maybe no ... and maybe the paragraph above is a better way to go ?

It's also an option to manoeuvre visually around the objects in VMC

If you have a couple of big rocky bits well to one side or the other, fine .. if you plan to eyeball it over the obstacles ... good luck and rather you than me. Generally, just not feasible due to the shallow climb gradients OEI.

Or fly straight out over the sea

Not much good if you are in tiger country and need to get past some nasty terrain before you see blue underneath ..

There are many valid options

I am a bit of a conservative .. but, I suggest, there is only one valid OEI option (unless you any departing in a flat desert area with nil rocky bits as far as the eye can see) and that is to do the OEI escape sums before departure. Generally, this is not feasible for the line pilot so it falls (rightly) on operator management.

[aterpster]

TangoAlphaD:

If the SID ends at 6000' and I'm at 5000 when the donkey dies and early on in the SID and I'm obviously without doubt above the min gradient well maybe yes just hold at the end of it or pick up vectors.

At some terrain-laden airports vectors won't do you much good if you're below the controller's minimum vectoring altitude. The industry was recently reminded about that last December with EVA coming very close to a CFIT on Mt. Wilson northeast of KLAX. And, KLAX isn't what I would call terrain-laden.

[president]

There will always be the guys saying "yes but NOT if there is a giraf on the runway". True dat! We all agree that there are plenty of options, but not every single time. On a V1 cut in low vis there is one option. And everyone knows that. The discussion was interesting until it started with some OEI stuff nobody asked about.

[galaxy flyer]

Back to the original question, what isn't clearly specified is whether the gradient is required by ATC or national authority for some reason (noise, president's palace) OR is it an obstacle. Charting doesn't always make thus clear. Going back to prior life, US DOD charts would specify "minimum" for obstacle or "ATC required" for all else. Two very different problems. Average will work if it is purely an airspace issue and as long as you get to 4,000' by the required point. If it is an terrain generated minimum really means MINIMUM. That maybe how we got down into OEI problems here.

[aterpster]

FAA policy was changed a while back to no longer publish ATC altitudes.

[aterpster]

They don't at LAX either. The controller turned them in the wrong direction towards high terrain then leveled them off at 5,000 into an area of 7,700 MVA. We had a big thread about it last December.

That near-disaster illustrates that requesting vectors when dropping below the floor of a SID with OEI may not be a wise course of action if well below MVA. The area below MVA, especially in the vicinity of rising terrain, is mostly a void for the controller. In the U.S. they do have emergency obstruction video maps (EOVMs) but they have neither the fidelity nor obstacle clearance to do much good.