SID Climb Gradient : "Minimum or Average"
 

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.

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

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.

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.

To back up the president...

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:

You might want to have another look at your maths.

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.

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

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.

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).

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.

Why would they bother? The company EO procedure may well ignore the SID requirements...

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''.

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

Thank you for that.

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.

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

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.

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.

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?