[A320] THR RED/ACC ALT

[k.swiss]

Hello

Last year we changed our SOP to thrust reduction altitude at 800FT accelerate at 600FT. (European operator)

What are the implications for this as now acceleration phase occurs after thrust reduction, which is not NADP1 (800/300) or NADP2 (800/800) compliant.

Thanks in advance for your inputs.

*Also as recalled in old FCOM, MCDU will not accept acceleration that is lower than thrust reduction. Perhaps this has changed with new software standards.

[john_tullamarine]

thrust reduction altitude at 800FT accelerate at 600FT. ..... acceleration phase occurs after thrust reduction

.. or did you mean vice versa ?

If you are AEO and the ops eng folk have checked that the revised procedure will keep you above the OEI profile, I wouldn't be too concerned.

Otherwise, if it isn't reflected in an AFM procedural change, I would be quite concerned.

[iggy]

The day you are taking off with low weight, using TOGA, and having a low initial altitude you may end up having a surprise...

I'm not saying it is wrong, I'm saying I have never heard of it.

[vilas]

Last year we changed our SOP to thrust reduction altitude at 800FT accelerate at 600FT. (European operator) What are the implications for this as now acceleration phase occurs after thrust reduction, which is not NADP1 (800/300) or NADP2 (800/800) compliant.
I think you mixed this up a bit. Generally it's the other way around.
These are fuel saving initiatives. Many airlines have 400/400ft. With low THR RED altitude engine failure above THR RED altitude may not meet required performance at MCT unless calculated for each airfield or simpler way is to reselect TOGA which will ensure that. The FMGC will transit to GA phase which will have to be brought back. You can refer to a video on airbuswin on this.

[john_tullamarine]

simpler way is to reselect TOGA which will ensure that

Albeit that the procedure is above 400ft, that probably is a bit contrary to the design standards implications/philosophy - FAR 25.111(c)(4) is relevant. I would not want to have to argue the point in court against a sharp barrister after a mishap which involved such a procedure..... unless it were specifically given the OK by the relevant regulator.

[vilas]

simpler way is to reselect TOGA which will ensure that

Albeit that the procedure is above 400ft, that probably is a bit contrary to the design standards implications/philosophy - FAR 25.111(c)(4) is relevant. I would not want to have to argue the point in court against a sharp barrister after a mishap which involved such a procedure..... unless it were specifically given the OK by the relevant regulator.
If engine failure happens above THR RED altitude of 400ft after thrust is reduced to climb then what I said is recommended by Airbus in the video I mentioned with explanation. The videos are especially meant for Instructors. Airbuswin is a free app. You can see it for yourself.

[john_tullamarine]

Indeed. I am a little more conservative and still would not relish having to argue the decision.

[vilas]

Indeed. I am a little more conservative and still would not relish having to argue the decision.
What would be your exact concern about TOGA at 400ft. not providing the required one engine performance? As explained in the video the flight profile AEO till 400ft will always be above the OEI profile with engine failing at V1. In case engine fails now at or above 400ft the selection of TOGA should always keep above that. The issue in Airbus is since the acceleration phase has started the system will suggest MCT thrust and this may not provide required gradient. Selection of TOGA thrust apart from max thrust reselects Speed Reference System which stops acceleration and resumes fixed speed climb. This should always provide a performance above the one provided by failure at V1.

[k.swiss]

Thank you all for your inputs, I will surely read each one definitively in some time.

To clarify to those who think I am mixed up, indeed I thought so too as in the old software the MCDU would not accept an input where THR RED was above ACCEL height. However this is indeed the proceedure 800/600 THR RED/ACCEL.

Threat #1:
As iggy said indeed on a day when low weight and TOGA (or even FLEX) this may cause an unwanted surprise as the aircraft accelerates to 250KIAS and thrust is still maintained in TOGA, causing overspeed with little time to retract flaps. Only mitigation is that this will happen over a 200FT margin. (800/600FT)

Furthermore as I have not had a chance to try this can someone kindly clarify if on the MCDU PERF TO page that it will accept 0800/0600 as the values?

[john_tullamarine]

What would be your exact concern about TOGA at 400ft. not providing the required one engine performance?

Not concerned about the physics at all. Rather the potential problem is procedural. In a relatively high workload and potentially terrain critical situation, the procedure puts additional load onto the operating crew for no airworthiness /design standards benefit. An ideal situation for a screw up, methinks. In my insular view, let's leave things in a stock standard, trained for, sequence - third segment completed, MCT, and into the fourth segment, just like in the sim .... habituation is a very strong driver in high stress response.

As explained in the video the flight profile AEO till 400ft will always be above the OEI profile with engine failing at V1.

One would expect that to be the case. However, I have seen operating techniques where this is not the case due to deliberate low level acceleration.

The issue in Airbus is since the acceleration phase has started

Indeed. However, this conservative engineer and pilot simply prefers a simpler operational protocol.

As to arguing the toss, I can see a well-briefed barrister heading straight down the pathway I have suggested. Having seen some torrid courtroom practice in the past, we really don't need to expose our pilot selves to such staged antipathy.

However, more than happy to agree to disagree.

[sonicbum]

Thank you all for your inputs, I will surely read each one definitively in some time.

Furthermore as I have not had a chance to try this can someone kindly clarify if on the MCDU PERF TO page that it will accept 0800/0600 as the values?

“The flight crew can modify the value. The minimum value is 400 ft above runway elevation, and it can be higher than, or equal to, or lower than THR RED.”

[WhatShortage]

What would be your exact concern about TOGA at 400ft. not providing the required one engine performance? As explained in the video the flight profile AEO till 400ft will always be above the OEI profile with engine failing at V1. In case engine fails now at or above 400ft the selection of TOGA should always keep above that. The issue in Airbus is since the acceleration phase has started the system will suggest MCT thrust and this may not provide required gradient. Selection of TOGA thrust apart from max thrust reselects Speed Reference System which stops acceleration and resumes fixed speed climb. This should always provide a performance above the one provided by failure at V1.
AEO on flex will always be above OEI on TOGA? Just asking, quite curious about that one, which I guess it's a yes.

[john_tullamarine]

AEO on flex will always be above OEI on TOGA?

I wouldn't make that a categoric statement as it will depend on a number of considerations - both engine and operational and, perhaps, individual aircraft systems logic.

[vilas]

AEO on flex will always be above OEI on TOGA? Just asking, quite curious about that one, which I guess it's a yes.
The takeoff path with AEO even with Flex is obviously above the path with OEI at V1. The question is about the path with one engine failing at 400ft after thrust reduction and MCT on live engine. This may not meet the requirement. Selecting TOGA will because the aircraft is already above the OEI at V1 path.
In case of the original question the acceleration has started at 600ft (Airbus) but the thrust is still at TOGA/FLEX till 800ft. Here the acceleration needs to be stopped which can be done if TOGA by selecting speed on the FCU, if in Flex select TOGA which will bring back SRS.