View Full Version : A320 questions coming up

22nd Oct 2015, 18:39
I have a couple of questions ,need some clearity on them.

1. In external pneumatic start ,if the pressure is low you can use two external carts in parallel.how do two external pneumatic carts work in parallel,has anyone had any experience with these.

2.In start valve fault ,supplementary procedures ,it states use cabin for contact with ground crew .Ambiguity here.

3.in an hp bleed valve fault ,the Mel States to open cross bleed and turn affected bleed off ,why is this ?

4.i have noticed some crew taking Apu bleed on just as the aircraft is taxing in to park and than turning off both engines rather than parking the aircraft first and taking APU bleed on than shutting engines off which is the proper way.

5.how to know which fmgc is master ,does It depend on which side is the ap on.

6. in line flying often at parking we get 1fd- ,so we try to simultaneously switch both FDS off and than try to turn them on .why is this done simultaneously ,though the computer reset table doesn't state this technique of simultaneously switching fds off .

7. Last but not the least sometimes in approach I've seen some crew manually setting a higher v approach when they saw that they are too close to the vls, they increase it by 2 or even more , isn't the gs mini suppose to cater for speed reduction .

22nd Oct 2015, 19:20
1. Surely that's a problem for the ground crew to solve.
2. If you will be using the service interphone system you'll need to transmit via CAB. I've never done this, comms were always via the flight crew interphone system to the ground handler, never directly to the engineer.
3. It take me longer to explain than for you to read the apropriate chapter in FCOM ;)
4. 'Select APU bleed ON just before engine shutdown'. A question of interpretation. I agree with you that 89% of the crews do it too soon.
5. FCOM explains states this.
6. No idea, never heard of this.
7. With GS mini working as it should you will land at Vapp so GS mini is not going to save you from a Vapp which is too low. GS mini doesn't 'cater for speed reduction'. Read the FCTM, it clearly explains GS mini.

22nd Oct 2015, 22:52
1. I am not aware of any specific flight crew procedure for this. At times, when performance of the ground pneumatic source was "marginal" (FCOM words) I got away with MAN ENG start and shedding the loads. More often than not they did not have second ASU anyhow. :E

2. Interphone to engine nacelle's audio socket which is connected to CABIN INT circuit.

3. To close off the bleed completely.

4. Your sequence is correct, Airbus recommends to minimize use of APU bleed with engines running to prevent ingestion of exhaust gases into airconditioning system. The only reason I heard for selecting it soon was "because you may forget to put it on". :ugh: go figure.

5. AP = OFF -> FMGC 1; AP = ON -> onside FMGC. Standard Q for Airbus theoretical knowledge course.

6. Bangalore incident, after that the OPS procedure had been standardized to hande both FDs simultaneously. No such AFM limitation or technical reason. Personally I would not force handling both FDs "at once" for resets, especially where FCOM / QRH state the opposite.

7. Those people think that Vapp calculated by FMGS is wrong and FAC-driven Vls as displayed on the speedtape is correct. Sometimes that is true, sometimes not. I never corrected and whenever the landing was bad, believe me it was not because of 2 knots difference on the speedtape. Anyhow, GS mini has nothing to do with this. Your best reference would be the FCOM bulletin (at the end of the book).


tubby linton
23rd Oct 2015, 12:31
FCOM bulletins do not exist any more. The pertinent information has now all been transferred inro the main fcom text.

23rd Oct 2015, 12:43
FMGC logic as explained in Auto flight:
1. Whichever AP is ON that FMGC is master.
2. If both APs are on FMGC1 is master.
3. If AP is off and FD1 is ON FD1 is master.
4. In flight FDs are switched off together to put ATHR in speed mode. It may be done one by one but some airlines prefer one person doing them. Yes that was one reason the crash could have been avoided. Reset of FMGC should be done one at a time.
5. By manually setting higher speed means amending Vapp in MCDU strong winds is recommended between 5 to 15KTS but increasing because it is close to Vls is an individual idiosyncrasy. GS mini will only come in ifexperienced head wind is higher than reported tower wind.

24th Oct 2015, 09:06
7.) As mentioned GS mini is a completely different concept. It is more concerned with maintaining a constant "energy" level of the aircraft which more or less translates to a constant ground speed. This, so that in the event of a sudden wind loss/gain, the aircraft doesn't have too much speed catching up to perform.

VLS as displayed on the MCDU and calculated by the FMGS is based on the weights input and determined by us at the INIT stage. Managed Vapp speed (the default target speed as displayed on the PFD) is derived from the same. The VLS shown on the PFD speed scale is determined by the FACs which principally derive their information from the AOA vanes. The FACS provide an actual value for VLS (based on the actual weight) whilst the FMGS provides a predicted value for Vapp. The predicted value of course can only be accurate if the loading was done correctly and if the calculated masses are accurate.

We fly heavy A321s on the standard bucket and spade destinations where most women are not the 70kg they're meant to be and where after duty free the aircraft is always going to be heavier than it's supposed to be. All of this makes standard masses next to useless. On older A32xs, Airbus decided that the FMGS would be the basis for the Vapp speed. However, I believe the newer ones have a better logic that blends a bit of actuality (FAC deduced VLS) with predictions (FMGS) to give us a more accurate managed Vapp speed. We still fly a fewer older A321s and our SOP says that once fully configured, to look at the PFD VLS value, then increase the Vapp to be at least VLS + 5.

24th Oct 2015, 13:39
As of about 6 months ago on newer aircraft the PFD VLS is now taken from the FMGC as well. If this fails the FACs are used as a backup.

25th Oct 2015, 11:07

Our SOP is that if the PFD does not display a 5 knot split (between VLS and VAPP) then we should adjust the VAPP accordingly.

25th Oct 2015, 11:19
Exactly,planes with sharklets get info about speed from FMGS

25th Oct 2015, 12:41
4. In flight FDs are switched off together to put ATHR in thrust mode .

All this time , I thought that it to ensure ATHR defaults to SPEED mode .

GS mini will only come in ifexperienced head wind is higher than reported tower wind.

G/S mini doesn't vary with different headwind , it's a simple one time calculation . IAS target adjusts .

25th Oct 2015, 13:56
Just to Clarify

Newer Aircraft:
VLS: "Computed by the FAC based on FMS weight data, and on aerodynamic data as a backup, and corresponds to 1.13VS....."

Older Aircraft:
VLS: "Computed by the FAC, based on aerodynamic data...."

So computation is still done by the FAC but now using the FMS weight data.

From the Older "Aerodynamic Data"
FCOM DSC-22_40-30:
"The accuracies of the various minimum and maximum speeds are functions of the accuracy with which the FAC computes aircraft gross weight. Normal accuracy for VLS in CONFIG FULL is about +-3kts"

So this basically means that the VLS and hence VAPP is going to be much more accurate in the newer aircraft.

26th Oct 2015, 00:38
Off course FDS off gets you in speed mode. It was an oversight. Thank you. I am correcting that. GS MINI is one time calculation but it keeps varying the Vapp only when the experienced wind differs.