Airbus dual engine failure - Why no yellow elec. pump on ?
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Airbus dual engine failure - Why no yellow elec. pump on ?
Hello
does anyone have an idea why airbus does not recommend using the yellow electric pump in the dual engine failure scenario after the APU is available ? I’ve seen a perfectly valid suggestion in an annoficial document that recommends switching the yellow electric pump ON after the APU becomes available and setting the PTU off as the load might be too much for the pump to handle . This aids especially in landing allowing flaps to be deployed as well .
does anyone have an idea why airbus does not recommend using the yellow electric pump in the dual engine failure scenario after the APU is available ? I’ve seen a perfectly valid suggestion in an annoficial document that recommends switching the yellow electric pump ON after the APU becomes available and setting the PTU off as the load might be too much for the pump to handle . This aids especially in landing allowing flaps to be deployed as well .
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I had asked this to Airbus. They do not have any objection. They replied that when windmilling RPM becomes low to cause Yellow system low pressure ECAM will ask to switch on yellow pump. Only thing is that the yellow Elec pump has fluid turn over of 65L/mt. as against 145L/mt of EDP so it is not capable of supporting the PTU.
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I had asked this to Airbus. They do not have any objection. They replied that when windmilling RPM becomes low to cause Yellow system low pressure ECAM will ask to switch on yellow pump. Only thing is that the yellow Elec pump has fluid turn over of 65L/mt. as against 145L/mt of EDP so it is not capable of supporting the PTU.
Any reason then for Airbus not to write this option as possible in the manuals?
Thanks!
Only half a speed-brake
My suggestion is it is a priorities/resources decision on the CRM side. Aviate (communicate), Navigate (communicate), Manage Systems (communicate).
In the Dual ENG failure: your goal is the PFD, ND, EWD in that order, and not SD - OVHD. There needs to be a cut somewhere so that you can restart scanning from the top item again.
Why not a technical note somewhere in FCTM? The manuals need to be kept simple so the readers will see the trees and not get lost in the background noise. Remeber the days of 9-item Golden Rules? Turns out they were too much to handle.
In the Dual ENG failure: your goal is the PFD, ND, EWD in that order, and not SD - OVHD. There needs to be a cut somewhere so that you can restart scanning from the top item again.
Why not a technical note somewhere in FCTM? The manuals need to be kept simple so the readers will see the trees and not get lost in the background noise. Remeber the days of 9-item Golden Rules? Turns out they were too much to handle.
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In the case of an all engines failure, the YEP can only be used if the APU generator supplies the electrical network. But, as per MMEL, the APU, the APU Generator and the Yellow Electric Pump are GO IF items. As a result, aircraft may be dispatched with one of these items inoperative.
Consider the cases of no fuel remaining (APU, even if operative, not able to start) or leak on the yellow hydraulic system subsequent to the Engine failure. In these cases, the flight crew will not be able to use the YEP in flight. As a result, use of the YEP in the case of an all engines failure would require additional system assessment and monitoring by the flight crew before they set the YEP on.
If fuel remains, if the yellow hydraulic system is in good condition, if the APU, the APU generator and the YEP are operative and usable at the time of the all engines failure event, then, the PTU must be switched off in order to isolate the green and the yellow systems. The YEP alone cannot pressurize both systems: The yellow electric pump characteristics (pressure/delivery curves) and the PTU efficiency are such that the YEP may just supply the Yellow and Green systems leaks if the PTU remains on.
However, even if the PTU is switched off, the extension of flaps is theoretically possible, but the deployment will be slow and probably periodically stopped due to interaction with the priority valve, depending on the hydraulic demand of the other consumers. The priority valve will shut off the supply to the flap motor in the case of low system pressure to protect the primary flight controls: As a result, the flaps may extend to an unknown position. The effects of such fluctuations of the yellow hydraulic pressure on the aircraft operation depend on many parameters and are not predictable.
If the Pilot Monitoring (PM) is distracted, and doesn’t manage to obtain the proper hydraulic system configuration, the aircraft might end up flying in a configuration with unknown results (i.e. YEP supplying both yellow and green hydraulic systems).
All engines failure event is a very demanding situation. During this short period of time, the crew's major concern is to attempt engines relight and/or to find a suitable landing field. Despite the potential benefits that could be envisaged from the use of the YEP in some very specific conditions, it is not worth complicating the procedure for the majority of cases and most probable scenarios.
For all the above reasons, Airbus did not opt for the use of the YEP in the procedures addressing the all engines failure situations (EMERGENCY LANDING procedure and ENG DUAL FAILURE procedure).
Consider the cases of no fuel remaining (APU, even if operative, not able to start) or leak on the yellow hydraulic system subsequent to the Engine failure. In these cases, the flight crew will not be able to use the YEP in flight. As a result, use of the YEP in the case of an all engines failure would require additional system assessment and monitoring by the flight crew before they set the YEP on.
If fuel remains, if the yellow hydraulic system is in good condition, if the APU, the APU generator and the YEP are operative and usable at the time of the all engines failure event, then, the PTU must be switched off in order to isolate the green and the yellow systems. The YEP alone cannot pressurize both systems: The yellow electric pump characteristics (pressure/delivery curves) and the PTU efficiency are such that the YEP may just supply the Yellow and Green systems leaks if the PTU remains on.
However, even if the PTU is switched off, the extension of flaps is theoretically possible, but the deployment will be slow and probably periodically stopped due to interaction with the priority valve, depending on the hydraulic demand of the other consumers. The priority valve will shut off the supply to the flap motor in the case of low system pressure to protect the primary flight controls: As a result, the flaps may extend to an unknown position. The effects of such fluctuations of the yellow hydraulic pressure on the aircraft operation depend on many parameters and are not predictable.
If the Pilot Monitoring (PM) is distracted, and doesn’t manage to obtain the proper hydraulic system configuration, the aircraft might end up flying in a configuration with unknown results (i.e. YEP supplying both yellow and green hydraulic systems).
All engines failure event is a very demanding situation. During this short period of time, the crew's major concern is to attempt engines relight and/or to find a suitable landing field. Despite the potential benefits that could be envisaged from the use of the YEP in some very specific conditions, it is not worth complicating the procedure for the majority of cases and most probable scenarios.
For all the above reasons, Airbus did not opt for the use of the YEP in the procedures addressing the all engines failure situations (EMERGENCY LANDING procedure and ENG DUAL FAILURE procedure).
I have heard that a pre-employment sim check on the A330 in Asia a few years ago used this scenario. With multiple failures the yellow pump helped get the thing on the ground.
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If you’ve adopted a particular speed to glide to a suitable landing point and CONFIG 2 has been selected then slats but not flaps will have deployed. The selection of the Yellow pump would cause the flaps to run out. Wouldn’t this decrease glide range? Always thought this was the logic behind the airbus procedure.
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The selection of the Yellow pump would cause the flaps to run out. Wouldn’t this decrease glide range? Always thought this was the logic behind the airbus procedure.
Only half a speed-brake
Chicken/egg, I'd say. Do you want to land slow but short, or fast and long?
USE FLAPS 3 - SLATS AVAIL ONLY: engineers who designed the ABN PROC already understood that 2+0 would result. BTW the difference on approach speed compared to 2+3 seems to be 15 kts. Earl's contribution above gives all the answers I personally needed.
Even if on a short final (below 3000 ft with LG down) and looking good, the idea to tweak it with YEP and trailing edge flaps is not the smartest.
F2 from 0 have massively significant balloon effect and pitch down moment, while at that stage it is DCT law with NO MAN TRIM. Apart from handling the disturbance itself, lack of remaining elevator authority for the touchdown would be an issue.
Agreed on the controlled flare being what defines the survability.
USE FLAPS 3 - SLATS AVAIL ONLY: engineers who designed the ABN PROC already understood that 2+0 would result. BTW the difference on approach speed compared to 2+3 seems to be 15 kts. Earl's contribution above gives all the answers I personally needed.
Even if on a short final (below 3000 ft with LG down) and looking good, the idea to tweak it with YEP and trailing edge flaps is not the smartest.
F2 from 0 have massively significant balloon effect and pitch down moment, while at that stage it is DCT law with NO MAN TRIM. Apart from handling the disturbance itself, lack of remaining elevator authority for the touchdown would be an issue.
Agreed on the controlled flare being what defines the survability.
Last edited by FlightDetent; 8th Sep 2019 at 09:57.
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This was the reply for whatever the worth
Obviously, when both engines are lost, and if enough fuel remains on board, the flight crew does everything to restart the engine using the windmilling. If it is not successful, the flight crew starts the APU and tries to restart the engines using the APU bleed. Therefore, if the engines are restarted, there is no need to use the Yellow Electrical Pump and the PTU.
If both engines cannot be restarted, we can identify 2 cases depending on the aircraft speed and the windmilling:
• We tried the Dual Engine Failure scenario in a simulator and the speed observed was between the ECAM recommended speed (280 KT) and the Green Dot Speed (220 KT in our example): The windmilling was enough to pressurize the green and yellow engine driven pumps. Therefore, in that case, thanks to the windmilling, there is no need to use the Yellow Electrical Pump.
• When there is not enough windmilling (it is the case in approach phase, for instance), the green and yellow engine driven pumps are no longer pressurized, and therefore the HYD G+Y SYS LO PR alert will appear on the ECAM. This alert will request the flight crew to switch OFF the PTU and to switch ON the Yellow Electrical Pump (if yellow sys lost by ENG 2 PUMP LO PR, which is the case in a Dual Engine Failure). This will enable to recover the systems supplied by the yellow hydraulic pressure, such as the alternate braking system.
For your information, if the Yellow Electrical Pump is started with PTU ON, then the PTU will run to pressurize the green hydraulic system. However, the flow delivered by the yellow electrical pump is low (32 l/min) compared to the flow delivered by the engine driven pump (140 l/min). Since the yellow pressure is used to pressurize the PTU, the yellow pressure drops down and by consequence the green pressure as well. Thus, if the PTU is not switched OFF, the HYD G+Y SYS LO PR will remain.
Obviously, when both engines are lost, and if enough fuel remains on board, the flight crew does everything to restart the engine using the windmilling. If it is not successful, the flight crew starts the APU and tries to restart the engines using the APU bleed. Therefore, if the engines are restarted, there is no need to use the Yellow Electrical Pump and the PTU.
If both engines cannot be restarted, we can identify 2 cases depending on the aircraft speed and the windmilling:
• We tried the Dual Engine Failure scenario in a simulator and the speed observed was between the ECAM recommended speed (280 KT) and the Green Dot Speed (220 KT in our example): The windmilling was enough to pressurize the green and yellow engine driven pumps. Therefore, in that case, thanks to the windmilling, there is no need to use the Yellow Electrical Pump.
• When there is not enough windmilling (it is the case in approach phase, for instance), the green and yellow engine driven pumps are no longer pressurized, and therefore the HYD G+Y SYS LO PR alert will appear on the ECAM. This alert will request the flight crew to switch OFF the PTU and to switch ON the Yellow Electrical Pump (if yellow sys lost by ENG 2 PUMP LO PR, which is the case in a Dual Engine Failure). This will enable to recover the systems supplied by the yellow hydraulic pressure, such as the alternate braking system.
For your information, if the Yellow Electrical Pump is started with PTU ON, then the PTU will run to pressurize the green hydraulic system. However, the flow delivered by the yellow electrical pump is low (32 l/min) compared to the flow delivered by the engine driven pump (140 l/min). Since the yellow pressure is used to pressurize the PTU, the yellow pressure drops down and by consequence the green pressure as well. Thus, if the PTU is not switched OFF, the HYD G+Y SYS LO PR will remain.
Last edited by vilas; 8th Sep 2019 at 13:12.
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This was the reply from the Airbus for whatever the worth.
Obviously, when both engines are lost, and if enough fuel remains on board, the flight crew does everything to restart the engine using the windmilling. If it is not successful, the flight crew starts the APU and tries to restart the engines using the APU bleed. Therefore, if the engines are restarted, there is no need to use the Yellow Electrical Pump and the PTU.
If both engines cannot be restarted, we can identify 2 cases depending on the aircraft speed and the windmilling:
• We tried the Dual Engine Failure scenario in a simulator and the speed observed was between the ECAM recommended speed (280 KT) and the Green Dot Speed (220 KT in our example): The windmilling was enough to pressurize the green and yellow engine driven pumps. Therefore, in that case, thanks to the windmilling, there is no need to use the Yellow Electrical Pump.
• When there is not enough windmilling (it is the case in approach phase, for instance), the green and yellow engine driven pumps are no longer pressurized, and therefore the HYD G+Y SYS LO PR alert will appear on the ECAM. This alert will request the flight crew to switch OFF the PTU and to switch ON the Yellow Electrical Pump (if yellow sys lost by ENG 2 PUMP LO PR, which is the case in a Dual Engine Failure). This will enable to recover the systems supplied by the yellow hydraulic pressure, such as the alternate braking system.
For your information, if the Yellow Electrical Pump is started with PTU ON, then the PTU will run to pressurize the green hydraulic system. However, the flow delivered by the yellow electrical pump is low (32 l/min) compared to the flow delivered by the engine driven pump (140 l/min). Since the yellow pressure is used to pressurize the PTU, the yellow pressure drops down and by consequence the green pressure as well. Thus, if the PTU is not switched OFF, the HYD G+Y SYS LO PR will remain.
If both engines cannot be restarted, we can identify 2 cases depending on the aircraft speed and the windmilling:
• We tried the Dual Engine Failure scenario in a simulator and the speed observed was between the ECAM recommended speed (280 KT) and the Green Dot Speed (220 KT in our example): The windmilling was enough to pressurize the green and yellow engine driven pumps. Therefore, in that case, thanks to the windmilling, there is no need to use the Yellow Electrical Pump.
• When there is not enough windmilling (it is the case in approach phase, for instance), the green and yellow engine driven pumps are no longer pressurized, and therefore the HYD G+Y SYS LO PR alert will appear on the ECAM. This alert will request the flight crew to switch OFF the PTU and to switch ON the Yellow Electrical Pump (if yellow sys lost by ENG 2 PUMP LO PR, which is the case in a Dual Engine Failure). This will enable to recover the systems supplied by the yellow hydraulic pressure, such as the alternate braking system.
For your information, if the Yellow Electrical Pump is started with PTU ON, then the PTU will run to pressurize the green hydraulic system. However, the flow delivered by the yellow electrical pump is low (32 l/min) compared to the flow delivered by the engine driven pump (140 l/min). Since the yellow pressure is used to pressurize the PTU, the yellow pressure drops down and by consequence the green pressure as well. Thus, if the PTU is not switched OFF, the HYD G+Y SYS LO PR will remain.
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It really helps. Aside from flaps extension, you would have alternate braking with anti skid, waaay better than relying on 1000 PSI. Even if the priority valves prevent you from extending the flaps due to the hydraulic demand to the flight controls system, I believe its worth a shot. Worst case scenario you will remain in a dual hydraulic failure you already had in the fist place. Why waive such valuable resources in order to protect a system you had already lost? As Earl mentioned its probably not part of the procedure because the YEP depends of GO IF items, but they could’ve added a note mentioning it as a possibility on the FCTM.
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Even though ECAM covers it all. I believe this topic (YEP use in Dual ENG Fail) is worth a note on the FCTM. Its about having a full situational awareness in such a time critical emergency. I personally have learned more about it here than on the books, and we know they aren’t worried about sparing a few more pages rs
