A320 CofG THS

[Natstrackalpha]

Where would we get the intial cg THS setting for the man trim wheel prior to take off. The setting that takes into consideration WAT / GW / runway etc?

Please don`t say the computor in the office, spits it out.

If in the middle of nowhere, from which publication would you derive the setting?

Or is it simply in the green band (he asked provocatively).:)

[Stuck_in_an_ATR]

Could you be more specific with your question?

We normally obtain the T/O C.G. by entering loadsheet data (ZFW, ZF CG and FOB) into the FMGS. No flip charts needed. We then set the THS accordingly. Is that what you need to know?

[Stuck_in_an_ATR]

Since the original Q was re-written, I'll expand my answer... :)

The THS setting for T/O in the A320 is solely a function of T/O cg - ie. how the aircraft was loaded.

The value of T/O cg. is derived as described above, using the loadsheet data. The loadsheet is, indeed, usually spat out by a computer, but can also be calculated manually when 'in the middle of nowhere'

[Natstrackalpha]

We normally obtain the T/O C.G. by entering loadsheet data (ZFW, ZF CG and FOB) into the FMGS. No flip charts needed. We then set the THS accordingly. Is that what you need to know?

Yes, thats it exactly. Thank you very much - ATR

[Ollie Onion]

If you were stuck in the middle of nowhere with no automated way of producing the loadsheet you would have to complete a manual loadsheet.

Once you have completed the manual loadsheet you would have a resulting CoG position. There is then a 'graph' in the TOME (in our case on the checklist) where you can see which 'THS' to set.

[Natstrackalpha]

Thank you Ollie.

[junebug172]

Are you saying the airplane spits out its own THS setting?

[Stuck_in_an_ATR]

Are you saying the airplane spits out its own THS setting?


It does (sort of). You insert ZFW, ZFCG and Block fuel into the box and it calculates the TOW and T/O CG - you then set the THS accordingly. Heard that some newer Airbii set the THS for takeoff automatically, based on the FMGC calculation.

Another thing is that you get the T/O trim setting on your loadsheet and you could just set it too, straight from the paper. But at least at my outfit, the SOP is to use the value from the FMGS.

Either way, you still need a traditional loadsheet...

[Clandestino]

Are you saying the airplane spits out its own THS setting? Why not? For such-and-such weight and such-and-such C.G. you get such-and-such trim setting and it works. You can use FMGS or graphic balance sheet or standalone EFB or whatever. It is simple calculation.

[Valmont]

PER-LOD-WBA-LTS P 1/4. Especially P 4/4.

You should have one of these onboard to calcultate it "in the middle of nowhere", i did it during line training and do it from time to time.

There was a power outage at the airport we were operating out of a couple weeks ago, had to verify the manual loadsheet that they provided. So we did it on our own too.

First the MACZFW is calcultated by a computer or manually using the above method, then the MACTO is calculated using the fuel onboard. Some FMS will give it to you once you enter the MACZFW and FOB (MACTO), some won't so you either have to do it yourself manually, either enter it using the computerized loadsheet.

[junebug172]

Unless I missed something, THS setting comes from load planning or charts as the MCDU is incapable of calculating it.

[Stuck_in_an_ATR]

Unless I missed something, THS setting comes from load planning or charts as the MCDU is incapable of calculating it.


You must have missed something :8

The Bus MCDU is capable of calculating the T/O CG as described in posts above.

However, SOP's vary from operator to operator. AFAIR, the official Airbus way (as thaught in Toulouse) was:

- read the TO CG from the loadsheet
- look at the scale on the back of the QRH to convert TO CG value info the trim setting
- insert the obtained trim setting into TAKEOFF PERF page for reference
- set the THS after engine start

Our SOP:

- read the T/O CG from FUEL PRED page after eng start
- set the THS

The latter method is simpler/faster and eliminates the potential for error of setting the THS in the wrong direction (eg. 2 UP instead 2 DN).

On the other hand, Airbus must be the only airplane in the world, where simple things like setting the trim for takeoff get so complicated that they require a discussion... :ugh:

[junebug172]

I'm a bit lost here because our MCDU doesn't calculate a THS setting. The only thing we see is ZFW CG and that's it.

Do you actually show a TO CG setting?

[Stuck_in_an_ATR]

On our aircraft, you can read the T/O cg. from MCDU FUEL PRED page after engine start. This can be set directly on on the trimwheel, which has a cg. scale.

We have fairly new airframes though, no idea how it works on earlier models.

[Pilot talk]

On the 330-300 it sets THS automatically after Engine start,a a function of Cg,which sometimes is marginally different from the load sheet calculated Ths. my company SOP Is to set Ths from Load sheet.

[ahramin]

Pilot Talk automatically setting the pitch trim is an option on the 330-300, not all of them do this.

Airbus SOP states to set the trim from the CG shown on the ECAM. There have been incidents of rotation problems from setting pitch trim based on load sheet CG.

[thermostat]

It's interesting to note that the performance chapter for the A320 bases all the figures on a MAC of 33%. Seems to me that if you start off with a MAC of34%, the fuel burn will cause the MAC to decrease during the flight towards a lower number, say about 30% depending on the length of the flight. This will keep the MAC close to the book value of 33%. Since the performance figures are based on 33%, wouldn't it make sense to load the airplane to reflect this value?
Seems not many ops people, chief pilots etc pay much attention to this area.
Any comments?
T

[Meikleour]

thermostat: Performance figures used to always be calculated at a relatively forward C of G since that was the most adverse from the fuel consumption point of view - however better results can be obtained by loading to a more rearward C of G. Many operators do this. The A330/340 family actively manage the C of G to a rear target in flight by use of the Tail Trim Tank.

[junebug172]

I looked further into why my company doesn't use the MCDU's numbers and, instead uses the the numbers from the company.

Our aircraft are audited every few years to ensure a highly accurate BEW. Any add standard operating iems (galley carts, etc) are also tracked and you end up with a highly accurate OEW.

Using standard weights for bags, pax, and actual weight for cargo the ZFW starts to become less precise, but still good enough.

And I've been told using 6.7 for fuel instead of the aircraft's densitometer doesn't make for to big a difference.

Heck, we don't even refer to the MCDU's numbers to trap any WB errors.