a7ala
Topic Author
Posts: 336
Joined: Sun Jan 04, 2015 10:27 pm

One-engine operable climb gradients

Fri Jan 31, 2020 3:21 am

Hi,

Novice was hoping for rule of thumb on what climb gradients airlines would use for normal and then 1-engine operable operations for the B787 and A350 variants.

Thanks
 
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Starlionblue
Posts: 19634
Joined: Fri Feb 27, 2004 9:54 pm

Re: One-engine operable climb gradients

Fri Jan 31, 2020 3:51 am

It's not so much a question of what we "use", as in what the aircraft will do. That varies wildly depending on weight and atmospheric conditions. We don't target a climb rate in the initial climb. We just climb out at best angle for the weight and thrust, and we don't really know what the angle is. That being said, there are minimum requirements. Checking EASA regs, it just says the gradient with gear out for two-engine aircraft with an engine out "must be positive". Heh... With the gear up, it is minimum 2.4%. With both engines, it is 3.2% in the landing configuration (gear down and full flaps).*

A couple of turns with the Airbus landing performance calculation software tells me that on the A350, we might get 4½-5% with an engine out at typical weights.

Given a 2.4% minimum, it makes sense that a standard go-around gradient is 2.5%. However many places have steeper gradients due to terrain. For example, HKG has 7% on 07L due to the highest mountain in the territory being dead ahead. Unless you're very light, you can't do that with an engine out on the A330/A350.

So how do you get past the requirement? You can either use the 2.5% GA gradient minima, which are, wait for it, 1332 feet! Not very practical unless you only operate on gin-clear days. Or you can construct a specific engine out missed approach path (and SID) with better terrain clearance.

BTW I think you mean "1-engine inoperable".

Side note: The Airbus landing performance software has an option for "All Engines Flame Out". Weirdly, it omits the go-around calculation. :D

* Page 17. https://www.easa.europa.eu/sites/defaul ... ersion.pdf
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
GalaxyFlyer
Posts: 4668
Joined: Fri Jan 01, 2016 4:44 am

Re: One-engine operable climb gradients

Fri Jan 31, 2020 3:11 pm

OEI stands for One Engine Inoperative, which covers all multi-engine designs. Yes, twins are most common but the technical term continues.

More tech poop—as to take-off climb, there’s really two limits—WAT or certification limit—the 2.4% gradient (2.7% for tris, 3.0% for quads). The TOGW will be limited by pressure altitude and temperature so that, at a minimum, the OEI gradient meets those numbers. OR, if obstacles are governing, the TOGW is limited by the gradient the aircraft can achieve to clear those obstacles, commonly also a gradient. Using a special departure procedure to laterally avoid the obstacle is a possibility, as Starlionblue pointed out at HKG.

The vertical profile is then divided into four segments, but here lies madness.

Really, an AEI table?

GF
 
a7ala
Topic Author
Posts: 336
Joined: Sun Jan 04, 2015 10:27 pm

Re: One-engine operable climb gradients

Mon Feb 03, 2020 12:47 am

Thanks very much for your responses :)
 
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Starlionblue
Posts: 19634
Joined: Fri Feb 27, 2004 9:54 pm

Re: One-engine operable climb gradients

Mon Feb 03, 2020 12:53 am

GalaxyFlyer wrote:
OEI stands for One Engine Inoperative, which covers all multi-engine designs. Yes, twins are most common but the technical term continues.

More tech poop—as to take-off climb, there’s really two limits—WAT or certification limit—the 2.4% gradient (2.7% for tris, 3.0% for quads). The TOGW will be limited by pressure altitude and temperature so that, at a minimum, the OEI gradient meets those numbers. OR, if obstacles are governing, the TOGW is limited by the gradient the aircraft can achieve to clear those obstacles, commonly also a gradient. Using a special departure procedure to laterally avoid the obstacle is a possibility, as Starlionblue pointed out at HKG.

The vertical profile is then divided into four segments, but here lies madness.

Really, an AEI table?

GF


Not really an AEI table. :) Just that one of the ECAM alerts that can be selected under "ENG" is "ALL ENG FLAME OUT". It will modify the landing distance calculation based on what stuff you're missing, e.g. 2/3 hydraulic systems, brakes, flaps beyond 1, etc... VAPP of 170knots :shock:
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
OldAeroGuy
Posts: 3905
Joined: Sun Dec 05, 2004 6:50 am

Re: One-engine operable climb gradients

Mon Feb 03, 2020 9:01 pm

There is also the Approach Climb requirement of 25.121(d)

Among other specifications:
- one engine inoperative
- gear up
- flap setting stall speed no greater than 110% of the landing flap stall speed
- minimum climb gradient of 2.1% (Twin), 2.4% (Tri) or 2.7% Quad

Although this is named Approach Climb, it is more closely associated with the Go-Around Configuration and Performance.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
Posts: 3905
Joined: Sun Dec 05, 2004 6:50 am

Re: One-engine operable climb gradients

Mon Feb 03, 2020 9:33 pm

25.123 is the regulation for the net climb gradient associated with terrain clearance in the cruise configuration.

The net climb gradient in the cruise configuration with one engine inoperative and the remaining engine(s) at maximum continuous thrust is the gross climb gradient reduced by:
- 1.1% (Twins)
- 1.4% (Tris)
- 1.6% (Quads)

With two engines inoperative, the gross gradient is reduced by these increments:
- 0.3% (Tris)
- 0.5% (Quads)

Read the regulation for all the other configuration specification details.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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