A320 Takeoffs
 

In the Performance charts for takeoff in an A320, it says you have to take 3 degrees from the flex correction if you takeoff with air conditioning on.

Do all A320 pilots takeoff with both packs off for takeoff? Or do you just subtract the 3 degrees from the FLX thrust calculation?

Cheers

Very rarely would we take off with the packs off. Generally in mild climates such as western Europe there would only be a couple of days a year (if your lucky) when the temperatures would be such that you would need the increased performance or reduce the risk of getting an EGT exceedance. In the middle east, Africa and say the hotter parts of Southern Europe then it would be a regular occurence.

The basis way of determining the tabulated flex temp is to enter into the performance tables for the runway in use and find your take off weight. You would have your planned take off mass from your flight plan. We note down a series of weights and the associated flex temperatures and speeds in and around this planned take off mass. When the actual load sheet is delivered to the aircraft we can then select a tabulated flex temp which has a take off mass that is greater than the actual one from your loadsheet. To arrive at the corrected flex temp which you enter into the MCDU you need to correct for air conditioning (taking off the minus 3 you stated), pressure, and engine and engine/wing anti icing if they will be used. In the case of a wet runway then additional corrections will need to be made for this as well as to the V speeds.

EZY Airbus 319 Fleet, conduct every takeoff with the Pack's OFF. They are selected off just before line up and they are put back on after reduction to climb thrust (1500 ft AGL) with a 10 second interval to soften the blast for the benifit of the PAX. This is a fuel saving SOP and has been standard in the company for a few years. I think there are a few other BUS operators that use this SOP.:cool:

Indeed Packs OFF for all take-offs is standard at our outfit on the bus too, back on after CLB thrust with the minimum 10s interval between them.

Saves fuel, improves performance on a TOGA take-off and reduces maintenance costs as EGT is reduced. A little extra FLEX goes a long way to improving engine life especially if only a small thrust reduction from TOGA is being applied.

Oh really? :ooh:

THR RED is at about 1500ft, isn't it?

Would having the packs off up to this height cause discomfort to PAX?

Nope, not at all. Joe PPL flies his unpressurised Cessna around at 5000ft with no discomfort and once in the cruise in the Airbus, the cabin altitude is the equivilant of flying a cessna at around 7000ft.

And if you live in a city like Jhb then at 5000 ft amsl you would still be 600 or so feet below the ground! (FAJS elevation).
I used to buzz around in a Cessna at FL 100, so depending on the pressure could be anything up from there!!


Quick question, do you guys use Packs off on finals on the Bus, in the case of a go around?

Or if you move the Thrust levers all the way to the TOGA gate does this happen automatically?

Or alternatively is the power loss with packs on in this phaze of the flight negligable?

Been there, done that (CFM-56-5A and Bs). After a while, more frequent pack valve replacements caught up with fuel and engine life savings. We don't do that anymore. Now packs off only in very limiting conditions - short rwy, hot, high, heavy. Otherwise Tflx-5.

@antic81

CFM powered 319/320: no, no, yes. We always check go-around gradient requirements and climb performance with packs on. Only occasionaly we have to turn them off - in the sim, never in actual flying but then we don't fly to Kathmandu.

Change in Pressure is not the problem... rate of change is. As with most things on the 'Bus, pressurisation schedules are comlpex. 1 pack at a time causes less rapid Cabin V/S => greater comfort (= less discomfort ;) ).

No need. This is a "cost" issue, not really performance, esp at Landing Wt ;)

Doubt it "saves (much) fuel" :eek: It lets you use a higher "flex" => longer engine life, and/or reduced costs, especially if you have an engine maint contract based on cost v Flex.

In my Airbus flying, we always did packs off takeoffs in the A340 (needed the perfomance!), and very rarely in the BA A320 series (it's there e.g. out of ABZ if we need another ton or so MTOW)

NoD

Packs-off T/O
 

Just a reminder that the Outflow Valve closes during the take-off run, so the cabin does not climb with the aeroplane after take-off. The transition from packs-off to packs-on was always very smooth in my experience. But we only did it when we had a performance shortfall (BA). In fact, if memory serves, our default performance figures were with packs on; so switching them off required a positive increment to Flex Temp or RTOW.

CJ1234, the rate of change to cabin altitiude in an A320 is minimal with a pack-off takeoff , ie the airframe is better sealed but does leak but not the same as a C152.

Some older or a bit 'bent ' airframes may leak a little higher on the initial climbout-I have seen temporarily 1000fpm max cab alt rate just approaching 1500ft accel height.

p. s as for a go-around, the A320 is never landing climb limited on 2 engines.:D

I don't understand that

Which part CJ? With regards to the initial climbout with an observed cabin rate of 1000fpm vs aircraft rate of climb around 2500-3500fpm.

On our mixed fleet, 319, 20, 21, we normaly use packs on. On normal runways/routes throughout europe we still have max flex available.

However there is a variable correction, of so many dec C flex for low qnh (ie less than 1013 hPa), plus another fixed correction for engine anti ice on if appropiate.

Do any operators use APU air to run the packs and change air over and turn APU off after T/O?

I wouldn't have thought so - unless you're somewhere REALLY hot where you need A/C AND ALSO maximum performance from the engines.

It certainly wouldn't save fuel.


No idea what that means!

Landing Climb
 

Hi CJ1234,

Without wishing to put words into aulglarse's mouth, I think I know what he was getting at.

If memory serves, "Landing-Climb Limit" refers to the climb gradient achieved during a go-around with one engine shut down. On some twins, this can be limiting; particularly if you are returning for an immediate landing with engine failure, after a take-off at the RTOW.

Suppose you had needed engine-bleeds/packs off to achieve your desired take-off weight, the limiting factor being WAT (second-segment climb gradient). The go-around case must be taken into account. If single-engine climb gradient was limiting for the take-off, it may not be much better in the go-around case. Therefore, it has to be taken into account; i.e., you may need to turn the bleeds off for the approach. [That's where the APU may come in handy.]

Quote from aulglarse:
...as for a go-around, the A320 is never landing climb limited on 2 engines.

Hope it makes more sense now; but perhaps he meant "one engine"?
N.B. - In the absence of any data, I cannot comment on whether "the A320..." is ever landing-climb limited.


PS: On a normal approach into a hot-high airfield, some aircraft types may be more limited by the go-around climb gradient (which has to take an engine failure into account) than by the length of the runway. So on 3 and 4-engine types, the performance graph will stipulate the number of engines being used for the approach, and assume that one of them fails in the go-around.
Maybe that is why aulglarse referred to "two engines"?

<<alidad>>

Yes I have used this procedure...APU with bleed and packs on for takeoff when I was based in southern europe. Also frequently when I was based in BHX operating a 180 seat config 320 from runway 15 which is more limiting I have used TOGA packs off 1500' one pack on and then 10 secs later the second on. Incidentally this went against SOP which dictated pack 1 on at thrust reduction, pack 2 on at flap retraction but what the hey.

Actually thinking about it when I was wet leased to an operator based in Abu Dhabi I am pretty sure I used APU on with bleed for T/O but I can't remember from where, most of the runways I was flying 320s into were long. But there fuel wasn't really an issue, we flew 0.81 everywhere and tankered as much as possible but hey that is a different story entirely.

Chris, thanks mate but I actually meant the oppposite.

In the performance section( FCOM 3.05.35 ), the approach climb scenario to achieve a positive gradient of 2.5% is with one engine out at CONFIG 2 or 3 with air conditioning on and set to HIGH.


For example ( from the manual ): a go-around conducted at 1000ft pressure altitude with CONF 2 and an OAT of 40 Celcius can be achieved at a weight of 79.9 tonnes! CONF 3 is at 78.7t.

Pretty impressive considering MTOW can be up to 77 tonnes and MLW up to 66 tonnes-weights may vary with serial numbers/operators.

The time when things may turn ugly is being very heavy with one inop(as Chris posted) and an immediate return to land is required.

A case may arise where a level-off may be required with gear down and CONF3 ( QRH 2.43 tabulates restrictions in this case).


There is no limitation with both engines operating to achieve landing climb GRADIENT of 3.2% (CONF FULL gear down) as with the above example considering that one engine can perform more than the MTOW in certain conditions at 2.5% gradient.

So a go-around with 2 engines operating has no weight restrictions in terms performance unless you got yourself into a very ugly situation.

CJ, you may get to go-around on line with 2 engines operating, you'll be pretty impressed with the rate-of-climb. I had 5400fpm at 64t the other day.

If you get the chance, take a look at the QRH 2.25 for the Overweight Landing procedure with reference for a g/around weights at CONF 3.

I hope this clears up my original post.:8:8