APU operations

[cavaricooper 2,613]

Hi all:I was wondering about (RW) APU operations. From what I have read most airlines turn off the APU (and Packs 2 and 3) prior to engine start/takeoff. Yes, some use all 3 packs with no APU (performance allowing) and my carrier (BA) advocates Pack 2 take-offs with the APU powering the pack in isolation.On the way in, however, while SOP to start the APU on the taxi in, when do most operators change over to APU powering the electrics- once on stand, before shutdown, or on the way in before wheel-stop?I have used both ways and do not seem to have any issues either way....but would like to keep in line with (RW) operational procedures.Please chime in.......Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

[cavaricooper 2,613]

Sorry, re-reading the above post- the no APU for start is obviously a faux-pas. I meant, 1 pack only for start (usually Pack 1 for cockpit environmental control reasons) and then an APU off takeoff with only the one pack operating. This seems to hold tru for a lot of operators other than for BA which advocates the APU operational and feeding Pack 2 which is isolated thus eliminating the pack load from the engines. Sorry for the confusion!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

[Qavion 19]

Lots of variables here...Is ground power available?Is in-ground air available?What's the weather like? Hot/Cold?How fussy are the authorities with regards to noise/air pollution?Is it economical where there are no airport-supplied air/electrics to buy and maintain dozens of very expensive power carts and air carts (plus time-wastage/man hours fitting them)? Unfortunately, the bean counters seem to overlook these things when they compare the price of running APU's Vs the price running ground carts (they only seem to look at fuel costs). They also overlook the sick time when someone injures their back installing the power leads (they are heavy). Imagine wrestling a 20 foot Anaconda :( It's only when you are forced to use ground sources by airport regulations would you ever not want to use the APU on the line.When ground air isn't available and it's hot.. You have to consider the effect on the employees working inside the aircraft (health, morale, productivity, etc)Noise pollution? It's an airport.... Everyone should be wearing ear-protection anyway. If one of those ground air supply hoses pops off the connection, your ears will be ringing for hours.Actually, the 747 APU is relatively quiet compared to others. Perhaps it's the height/angle of the exhaust? I find 737APU's much noisier. The 777 has the exhaust coming out of the side of the tailcone (noisier, too, IMHO).On arrival, if you really had to use ground air/power, I would at least start the APU approaching the gate. Often there are busy roadways behind the aircraft (you don't want to hold up traffic behind the aircraft whilst you plug in ground power (prior to engine shutdown)).Common sense doesn't always dictate the outcome however.Cheers.Q> イアン

[cavaricooper 2,613]

Thanks Q- in addition, when does the transfer to APU electics and bleed occur. Obviously before engine shut-down, but do most operators wait until on stand, or does the transfer occur on the taxi in after APU Running annunciates on the EICAS? I have tried both and it doesn't seem to matter a whit- just wondering correct what RW SOPs are (and why).As far as long term APU operations, your post was hugely helpful, thanks again.Steve, Alex and other RW captains, please chime in as well.Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

[BAW9DV 2]

Carl,Last time I checked with my friends at British Airways (as you may know its practically impossible to get any written material on their SOPS), the APU is switched off immeadiately after successful startup of all four engines after pushback. Startup with the APU running is performed with PACKS ONE and THREE OFF. Packs are switched back to ON after successful start and the APU is then switched to OFF.On taxi, when the aircraft reaches the hold, prior to entering the takeoff runway, Packs ONE and THREE are again switched OFF as part of the before-takeoff checklist. After passing 3000 feet, all packs are set to ON and checked as part of the 10,000 feet checks.On the arrival, the APU again is usually switched ON leaving the runway because it requires some two to three minutes to spool up.When on stand and parked, the APU is left ON after the crew no longer require the engines running - and they are shutdown. When Ground Power is available and the ground crew on hand, the APU is then switched OFF. If the aircraft is going to the hanger and no longer required for flight in the succeeding 8 hours, the APU is swtiched OFF, irrespective of ground power - unless it is needed for other reasons.All this is for "normal" operations. There are changes to the procedure when the weather conditions change or other factors are present. As I understand it, there are variations to this procedure, depending on the different airlines. Cathay Pacific often take off with packs TWO and THREE OFF (once told to me by a former CX pilot I knew at LHR when I worked there).I'm still trying to get the definitive procedures, but its harder now I'm no longer at LHR....Hope ths is of some help.Cheers mate!Lee

[cavaricooper 2,613]

Thanks Lee!When does the transfer to APU Electrics occur? DURING the taxi in (after APU Running annunciates) or AFTER chocked? Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

[Krister 51]

In the Airtours 757-200 video from ITVV the captain asks for the APU to be started while they are still some 2000 feet up in the air and just have been handed over to Tower for the approach. I can't find any clue to why it's done so early, but it's interesting!

[VHOJT 167]

Hi there CarlOn the ITVV 747-400 Virgin Atlantic DVD, I believe they switch to APU power once the parking brake is set and before the fuel control switches are set to "Cutoff" (obviously). I think it is their first "Shutdown" checklist item.Also, just in case you didn't know, I read somewhere that British Airways uses a somewhat special climb procedure out of LHR on the 744:- T/O thrust (can be derated/assumed temp thrust) to 1,000ft- CLB thrust selected at 1,000ft, and MCP speed window opened and speed manually set to Flaps 10 REF speed + 10- Flaps retracted to Flaps 10 upon passing Flaps 10 REF speed. Aircraft will continue in this configuration until passing 4,000ft.- At 4,000ft, MCP speed window is closed, aircraft is accelerated, and flaps retracted- Once flaps are up, CLB-1 is selectedSorry if you already knew that, I just thought I'd let you know in case you didn't. Qantas also use a similar procedure I think, using max T/O thrust (no derate/assumed temp) until 1,000ft, then climbing with CLB thrust to 4,000ft until accelerating. Probably to make all those 4000A restrictions in the SIDs.CheersRudy

[cavaricooper 2,613]

Thanks Rudy! Yes, I have that video (superb- the best 744 video out there, folllowed by the Oasis one IMHO). I was just wondering if any operators switched in taxi, and why, or why not.....doesn't seem to make any difference to the a/c.Thanks for the BA procedures, I had read that before so confirmation is great!Best-Carl F. Avari-Cooper BAW0225http://online.vatsimindicators.net/980091/523.png

[Ralgh 43]

Based on experiences at the two airlines I have worked for procedures like these are often dictated by the fleet managers personal whim or desire to put his stamp on his time as manager. They sometimes change when a new manager takes over. The other thing sometimes airlines have their philosophy that is different from other airlines. At my current airline(American)we have been switching, over time, to exactly what the Boeing manuals say. That way when something goes wrong management can point to Boeing and say that how they said to do it and they are the ones that made the plnae. Of course there is always the odd ball thing like about two years ago our 737 fleet guys decided that we will put the flaps out during the push. We were never given a reason for the change and most Captains don't do it. It is possible to block the view of the push crew with the flaps down. I think that is a fleet manager whim because no other fleet at American does that.

[BAW9DV 2]

Hello Carl,>>Thanks Lee! When does the transfer to APU Electrics occur? DURING the taxi in (after APU Running annunciates) or AFTER chocked?<

[Triple7 1]

Afternoon,For BA it is:(Note paraphrased to only contain Bleed/Electrical/Hydraulic Info)Electrical PowerBus Tie Switches ... AUTOAPU Selector ... STARTAPU Gen 1 and 2 AVAIL Lights ... ILLUMINATEDAPU Gen 1 and 2 Switches ... ONBleed AirAPU Bleed Air Switch ... ONL and R Isolation Valve Switches ... ONPack Control Selectors ... AS REQ'DEngine Bleed Swtiches ... ONPush / Start ProcedureWhen ATC and start clearance are obtained:Hydraulic Demand Pump Selector No. 4 ... AUXHydraulic Demand Pump Selector No. 1 ... AUX/AUTOOnce start approvedPacks ... OFFAfter Start ProcedureAPU Selector ... OFFHydraulic Demand Pump Selectors ... AUTOPack Control Switches ... NORMBefore Takeoff ChecklistAir Conditioning ... SETFor takeoff>300,000KgPack Control Switches ... OFFFor all other takeoffsPack Control Switches ... NORMAfter Takeoff ProcedurePack Control Switches ... NORMExcept where performance requires otherwise, after climb power set and prior to reaching 3000ft AAL, place one pack control selector to NORM. Allow time for cabin rate to stabilise then, place the remaining pack control selectors in NORM.After LandingAPU ... AS REQDFor fuel exonomy, delay starting the APU until approaching the apron.

[Triple7 1]

>Also, just in case you didn't know, I read somewhere that>British Airways uses a somewhat special climb procedure out of>LHR on the 744:Noise Abatement Procedure1. Carry out standard takeoff procedure until 1,000ft AAL2. At 1,000ft AAL reduce power to full CLB power3. Speed intervene at flaps 10 minimum manoeuvring speed.4. Accelerate to flaps 10 minimum manoeuvring speed, restracting flaps to 10 on schedule5. Climb at flaps 10 minimum manoevring speed to the terminating altitude6. Terminate speed intervention and accelerate on schedule to en-route climb speed7. Once clean, reduce climb power to CLB1.

[BAW9DV 2]

Hi there,Sorry you don't give your name in the posting. Some of this is correct but some of it is in-correct.>>For BA it is:Electrical Power - All correctBleed AirPack Control Selectors ... AS REQ'D - These are always set to ON after APU startOnce start approvedPacks ... OFF- not for BA - packs ONE and THREE are usually selected to OFF with Pack TWO left ON under BA SOPs. The load is considered negligable.Before Takeoff ChecklistAir Conditioning ... SETFor takeoff>300,000KgPack Control Switches ... OFFFor all other takeoffsPack Control Switches ... NORM- again, Packs ONE and THREE are selected to OFF under BA SOPs prior to takeoff unless there is reason to select all PACKs to OFF as stated by you above.After Takeoff ProcedurePack Control Switches ... NORMExcept where performance requires otherwise, after climb powerset and prior to reaching 3000ft AAL, place one pack controlselector to NORM. Allow time for cabin rate to stabilisethen, place the remaining pack control selectors in NORM.- this is not usual for BA. However, it is dictated by both the conditions and the decision of the PIC - there are recommendations in the SOPs but this is perhaps one of the items that is left to the PIC in most cases as to how he proceeds.After LandingAPU ... AS REQD- APU is normally set to START and the APU bleed switch to ON, whilst the APU takes about 2-3 minutes to spool up - all during taxi to the gate.For fuel exonomy, delay starting the APU until approaching theapron.- see above.Take care,regards,Lee

[Triple7 1]

Evening Lee,Sorry for the delay.The information I posted above was directly from the latest version of the BA flying manual, so is fairly correct.However in order to authenticate it I have just spoken to a current senior captain on the jumbo with BA.Start - ALL the packs are turned off.Takeoff - ALL the packs are on unless the TOW is greater than 300T. In which case they perform an 'APU to pack' takeoff, where the APU is left running for the T/O to provide pressurization, the left and right packs closed, and the isolation valves closed.APU - normally as a rule 2 minutes before turning on stand.Cheers