all engines climb gradient tables & charted SID climb gradients

[Microburst2002]

Hi fellows

I had a discussion on the flight deck recently. My mate said that in an SID you have to make sure that you comply with the climb gradient requirements while you fly (by means of the gradient-GS-fpm table included in the chart) and I say that as long as you check in the all engine climb gradient table (company provided) that it is ok you before departure, you can just fly the departure normally without minding your gradient (within reason).

Any thoughts?

[AerocatS2A]

I say that you need to maintain the gradient while you fly, but there is more than one way of doing this. Staying at or above the FPM required for your ground speed is one way, but it is very conservative.

The climb gradient can be thought of as a physical floor that starts at 35' at the end of the runway and extends out along the take-off path at the nominated gradient. The only real way to know that you are meeting the climb gradient is to know how many feet per NM you need to gain from the end of the runway.

If you get airborne 2/3 the way down the runway then you are well above the gradient right from the start. Your initial climb is probably quite steep until you get to your acceleration height and so you're even further above the gradient. You can then afford to have a climb rate in fpm that is lower than the fpm/gs table suggests while you accelerate. Once you have cleaned up you are probably climbing quite steeply again.

You have a few options then.

1. Maintain the fpm from the fpm/vs table. This is easy, doesn't require any planning, and ensures you stay above the gradient required. But some aircraft automation systems don't lend themselves to this during the acceleration phase.

2. Check your company climb gradient tables and trust that any periods below the fpm required are more than made up for by the periods above. This is also easy but doesn't give you any guarantees. If you got below the gradient you wouldn't know it.

3. Know how many feet per mile the gradient actually is and monitor this with reference to a known point such as the DME. To do this accurately you also need to know and allow for the distance from the DME to the runway threshold. This requires some planning but is the most accurate and the most flexible as it allows you to reduce below the fpm/gs table while you accelerate while also ensuring you meet the gradient requirements.

I should add that checking the climb tables should be in all three of those options as you need to know whether the gradient is achievable before you depart.

I don't have any references to back this up other than the ICAO definitions for climb gradients for SIDs but the captain needs to ensure the aircraft is performing adequately and, as far as I can tell, those are his/her options for doing so.

Edit: Option 3 loses accuracy once you turn off the runway track.

[Microburst2002]

Normally the gradient is way steeper than the requirement. The headache comes at the acceleration height. It is weird that after many years flying "normally" now I have to use V/S mode a lot during that phase, instead of just letting the usual modes do their work. I don't think it is necessary unless you are truly limited.

The all engine climb gradients are valid for specific take off configurations and speeds at different elevations and ISA devs, all of which factors change during the climb (configuration, speed, and specially elevation) so what is the use of them? I always thought that if the gradient required in the SID was less that that of the table (for actual temperature and field elev) then you were ok to climb without worriying about that at all.

[FlightDetent]

MB2k2: My thoughts are with you. It sounds as if someone tried really hard to find an airtight solution to a problem that does not exist. (*) Hopefully the day will never come when the increased workload will be the last straw.

regards, FD.

[Willie Nelson]

To keep it simple for most gradients in Australia (happy to be corrected) the gradient is always going to be met in my light twin jet on two engines and on one engine the gradient does not apply as you would instead follow your published obstacle clearance procedure and simply make best endeavours to remain within Controlled Airspace with the assistance of ATC of course.

My outfit raises the acceleration altitude to a minimum of 800 feet to assist in AEO compliance, the rest becomes academic.

Maybe there's more to it?

[AerocatS2A]

It comes up in our "light quad" because if it is hot and we are heavy and we fully flex, the acceleration rate of climb is below the required and rate AND if you bother monitoring the physical gradient, distance vs altitude, it doesn't always make it. Depending on what you fly you may need to be aware of these things.

[SmallGlassofPort]

The OP does not mention his position hence we have no idea of the rules we are bound by.
Aerocat has summed it up pretty well. If Aus based read the AIP, it tells you how much clearance it gives you if the gradient is above 3.3. It might give you shivers if you cannot guarantee your gradient.
The long and short is, you must comply with the climb gradient! If you have escape procedures established that's great, but if the failure occurs after the escape turn point what will you do?
Most larger aircraft have the capability of up to 4% on one. Assuming it's a twin. As Aerocat has said through if they struggle to make it on all 4 on a flex takeoff, they have real problems..
I suggest any depiction of a gradient above 3.3 is likely to be of risk to the aircraft and it needs to maintain the minimum FPM. If it doesn't and for example following engine failure maintains level accelerate, legally where are they? They wouldn't know until above LSALT?
SID's are set for traffic movement and terrain/ATC LL clearance - when you abide by the SID.

Cheers All!

[underfire]

For those of you in AUS, if you are with Q, then you have the tailored departures to work with for OEI. With those, you can see the different flightpaths, and there are some that do not meet the "straight ahead until" parameters of the SID.
I actually wish that ICAO or the FAA would come up with a DEP criteria, but alas, I dont see that happening.
Tailored procedures used the 10 year high temp, and a combination of MTOW, all the bleeds turned on, and the engine type 20K/22K etc...spec. (5, 10 sec...)
The EO DEP are designed this way, adding turn performance, for the basis for the different NA above restrictions.

You have a 20K, 5 sec motors, its hot and you are heavy, you are going to be at double digit climb gradients....

[john_tullamarine]

I actually wish that ICAO or the FAA would come up with a DEP criteria, but alas, I dont see that happening.

Too many variables across many Types .. so it is likely always to remain with the PIC (ie operator, in general)

You have a 20K, 5 sec motors, its hot and you are heavy, you are going to be at double digit climb gradients....

.. can you run that one past us again ? (as an aside, I presume you are referring to 5/10 minute rating .. rather than second ?)