A320 APU start in Emerg Electrical Config
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A320 APU start in Emerg Electrical Config
Mate of mine posed this at me.
To start or not to start?
FOR
Once the emerg gen is up and running its possible to start the APU. Its better to have all your electrics back than simpley having only your ESS busses powered.
AGAINST
If youve lost your electrics all at once then something is seriously wrong in the electrics dept. The APU gen may be thrown off-line and all youve done is drain the batt during the start.
It'll depend on what the situation is at the time but I favor starting it if its a dual eng gen prob (for example a gen failure and the other a IDG failure simultaneusly) and NOT starting it if both gens are fine but are continuously being thrown off-line for no obvius reason.
Any comments?
To start or not to start?
FOR
Once the emerg gen is up and running its possible to start the APU. Its better to have all your electrics back than simpley having only your ESS busses powered.
AGAINST
If youve lost your electrics all at once then something is seriously wrong in the electrics dept. The APU gen may be thrown off-line and all youve done is drain the batt during the start.
It'll depend on what the situation is at the time but I favor starting it if its a dual eng gen prob (for example a gen failure and the other a IDG failure simultaneusly) and NOT starting it if both gens are fine but are continuously being thrown off-line for no obvius reason.
Any comments?
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Hi
Depends on which model of RAT (Ram Air Turbine) is installed.
The old type RAT will stall when the gear is lowered due to the disturbed airflow from the wheel assembly, and landing is made on batteries only. Therefore it is not recommended to start the APU as it uses the batteries to start which should be conserved for the approach with gear down.
The new RAT doesn't stall on gear down and therefore the batteries are not so essential and can be used for APU starting.
ECAM knows which RAT is installed and therefore prompts the pilots to start the APU if it is the new RAT, otherwise this ECAM action line is missing.
Hope this helps
Pro Spin
Depends on which model of RAT (Ram Air Turbine) is installed.
The old type RAT will stall when the gear is lowered due to the disturbed airflow from the wheel assembly, and landing is made on batteries only. Therefore it is not recommended to start the APU as it uses the batteries to start which should be conserved for the approach with gear down.
The new RAT doesn't stall on gear down and therefore the batteries are not so essential and can be used for APU starting.
ECAM knows which RAT is installed and therefore prompts the pilots to start the APU if it is the new RAT, otherwise this ECAM action line is missing.
Hope this helps
Pro Spin
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AGAINST
The APU gen may be thrown off-line and all youve done is drain the batt during the start.
The APU gen may be thrown off-line and all youve done is drain the batt during the start.
If the APU GEN is then thrown "Off Line" no adverse battery drain would have occurred. This is the reason for not attempting a start when "ON BATT" only.
Clarification: No adverse battery drain, meaning that the battery power used for start, should be replentished with the APU GEN running. The reason for not attempting an APU start on BATT only, is in the event that the APU doesn't start, thus decreasing the already minimal (30 min) battery life.
Last edited by Jimmy Do Little; 4th Aug 2009 at 11:59. Reason: Clarification
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So there is a substantial difference between the old type and the new type procedures: starting or not the APU.
However, the BATTs will keep charging as long as the EMER GEN is running, so what is the reason?
However, the BATTs will keep charging as long as the EMER GEN is running, so what is the reason?
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Thanks for the replys but woe a minute....
I dont see anything in FCOM or QRH that the APU batt drain is less with the EMER GEN running.
With EMERG GEN running.....
QRH 1.01 APU Elec Control Box for start/LP Fuel Valve/Fuel Pump
FCOM 1.24.10 P13 EMER GEN RUNNING diag
FCOM 1.49.30 P1 whole page
I cant see any evidance that the batt isnt drained (3.5 minutes) by a APU start while EMERG GEN running. Thats the way I always understooded it.
With referance to QRH 1.01 the list says what youve got remaining, not nesesarily what the RAT may or may not be powering.
Somethin being missed by yours truley here?
I dont see anything in FCOM or QRH that the APU batt drain is less with the EMER GEN running.
With EMERG GEN running.....
QRH 1.01 APU Elec Control Box for start/LP Fuel Valve/Fuel Pump
FCOM 1.24.10 P13 EMER GEN RUNNING diag
FCOM 1.49.30 P1 whole page
I cant see any evidance that the batt isnt drained (3.5 minutes) by a APU start while EMERG GEN running. Thats the way I always understooded it.
With referance to QRH 1.01 the list says what youve got remaining, not nesesarily what the RAT may or may not be powering.
Somethin being missed by yours truley here?
Last edited by Slasher; 28th Jul 2009 at 08:32.
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And the ECP is not supplied by the EMER GEN. It is fed from the DC BAT BUS. Only when you push the APU MASTER, the BATs will feed the DC BAT BUS (for 3 min) to permit APU starting. The DC BAT BUS is never supplied by the EMER GEN, and therefore the BATs will not be charged.
so: Is there any reason for not starting the APU after an emergency electrical configuration?
so: Is there any reason for not starting the APU after an emergency electrical configuration?
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You can not charge the batteries in the emergency elec config!
1) The emergency generator will never charge the batteries.
2) Even if you can start the APU you won't be able to get the power to the batteries because of the AC Bus failure
Normal config:
APU -> AC BUS 1(2) -> TR 1(2) -> DC BUS 1(2) -> DC BAT BUS -> Batteries
Emerg Elec Config
As you have no AC BUS 1 or 2 the power can not get to the batteries:
APU -> xxx -> xxx -> xxx -> xxx -> Batteries
Slasher had it right in his first post.
If you've got a generator problem - start the APU.
If you've got a double AC bus problem - do NOT start the APU.
Even the A330 (which has a totally seperate APU battery) does not recommend that you switch on the APU in the Emerg Elec Config.
Why?
Because despite having two working generators (on the engines) you are unable to recover either AC bus. An extra generator (APU) is very unlikely to make any difference.
You have a major electrical problem. Applying large electrical currents to faulty electrical systems is not a good idea! You are already having a bad day; the last thing you need is a further fault or fire.
If your TV went bang you wouldn't just plug it into another socket...
1) The emergency generator will never charge the batteries.
2) Even if you can start the APU you won't be able to get the power to the batteries because of the AC Bus failure
Normal config:
APU -> AC BUS 1(2) -> TR 1(2) -> DC BUS 1(2) -> DC BAT BUS -> Batteries
Emerg Elec Config
As you have no AC BUS 1 or 2 the power can not get to the batteries:
APU -> xxx -> xxx -> xxx -> xxx -> Batteries
Slasher had it right in his first post.
If you've got a generator problem - start the APU.
If you've got a double AC bus problem - do NOT start the APU.
Even the A330 (which has a totally seperate APU battery) does not recommend that you switch on the APU in the Emerg Elec Config.
Why?
Because despite having two working generators (on the engines) you are unable to recover either AC bus. An extra generator (APU) is very unlikely to make any difference.
You have a major electrical problem. Applying large electrical currents to faulty electrical systems is not a good idea! You are already having a bad day; the last thing you need is a further fault or fire.
If your TV went bang you wouldn't just plug it into another socket...
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If you've got a generator problem - start the APU.
If you've got a double AC bus problem - do NOT start the APU.
If you've got a double AC bus problem - do NOT start the APU.
Both generators, or both AC busses?
Our QRH (320 REV 37) just says: -APU (IF AVAIL) ..................START
They assume the RAT has extended, otherwise APU start will be impossible on batteries only inflight.
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Hi TyroPicard,
The ECB and APU starter are fed by the battery bus, which is not powered in emerelec config.
In fact, if you check the table of the systems remaining in emerelec, both on the QRH or the FCOM 3, you will see that with the EMER GEN RUNNING you can start it, but with BAT ONLY it is Inop.
I agree these manuals often suck, because they are made by engineers and not pilots...
They assume one must clearly see an important point like this one simply because it's in the table, instead of clearly stating so, in a more "pilot" way....
Please let me know if it's me who have missed something (quite plausible as I'm rather new on the Bus...)
LEM
The ECB and APU starter are fed by the battery bus, which is not powered in emerelec config.
In fact, if you check the table of the systems remaining in emerelec, both on the QRH or the FCOM 3, you will see that with the EMER GEN RUNNING you can start it, but with BAT ONLY it is Inop.
I agree these manuals often suck, because they are made by engineers and not pilots...
They assume one must clearly see an important point like this one simply because it's in the table, instead of clearly stating so, in a more "pilot" way....
Please let me know if it's me who have missed something (quite plausible as I'm rather new on the Bus...)
LEM
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Someone correct me if I am wrong but I believe that when the APU master is selected on it connects the DC Bat Bus for 3 minutes to permit starting regardless of if the Emer Gen is on FCOM 1.49.30.
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robbopilot. Yes that is correct. It is mentioned in the smoke/fumes removal procedure as a note after At FL100 or MEA - APU Master Sw On.
Ref PRO-ABN-26.
0-8 Good summary like it.
Ref PRO-ABN-26.
0-8 Good summary like it.
