airbus fmgc
 

hi all,

two small questions.

the first is on the airbus fmgs performance page for the approach the F,S and Green Dot speeds are displayed. On the Go Around page the speeds are given but the F speed is different from Approach page value. FCOM 4 states that the same speeds are diplayed on both pages. any reason for the difference?

the second is why on the 320 it is recomended to use the Dome light at dim for takeoff and on the 330 theres no mention of the dome light at take off?

thanx

the dome light should be on dim at night as (certainly on our old 320's)it's the only source of ilumination in elec emer config.

Elec. emerg. config? But that is not the reason you should have it on for take-off. I thought it was required incase of an rto followed by a pax evac. as soon as you shut down the 2nd engine the dome light is the only cockpit lighting available....

Anyone got an FCOM reference for leaving the dome light on ?

Without looking into it more carefully and just a quick reply here, perhaps the G/A F speed is different as it is the F speed with 1 flap less? Ie not full but Flap 3. Whereas the F speed is for the fully config App speed? Just a thought! Regarding the A330 lighting, the STORM is hotwired to the bats and so why not either turn it on when you need to or use your torch that you can never get to as your Nav bag is in the way. Absolutely a nonsense reason to leave light on for T/O, don't we turn OFF the LANDING LIGHT when landing in FOG if it's distracting, so why have the O/H lights on if not wanted for T/O?

@westinghouse
 

the first is on the airbus fmgs performance page for the approach the F,S and Green Dot speeds are displayed. On the Go Around page the speeds are given but the F speed is different from Approach page value.

I'm not current on 330, but maybe it has to do with 1.3 VS for landing and 1.2 VS for takeoff/GA.

So, are F, S and Green Dot speed higher on Go Around Page?

It has been many years since the 'bus but I believe the panel lights on the 330 came on during a rejected take off. Not so on the 320. Corrections welcomed.

The new dome-lite rule is to provide lighting to the Stby Insts in case of wiggly-amp disaster.

A330 FCOM 3.04 quote
 

Airbus states in their A330 FCOM - Operating Speeds Definition:
"F : Minimum speed at which the flaps may be retracted at takeoff. In approach, used as a target speed when the aircraft is in CONF 2 or CONF 3. Represented by “F” on the PFD airspeed scale. At takeoff, it is equal to about 1.18 VS of CONF 1 + F, and is limited to a minimum of VMCL + 5 knots. In approach, when the aircraft is in CONF 2, the takeoff value is increased by 14 %. It is limited to a minimum of VMCL + 15 knots and to a maximum of VFE CONF 3 - 2 knots. Then, when the aircraft is in CONF 3, the takeoff value is increased by 4 %. It is limited to a minimum of VMCL + 10 knots and to a maximum of VFE CONF FULL - 2 knots."

Oh, and indeed: on the A330, after an RTO, or on the ground if the batteries are the only source of power; the Dome light indeed illuminates.

330 Question
 

Now that the 330 is the topic of discussion here can someone plz enlighten me as to why on the 330 are there 2 buttons namely the ALT Button (in place of EXPED) on the 320 and the Push to level off/ VS button on the FCU there for exactly the same function ,

and correct me if I'm wrong new airbus trg policy now teaches the crew to hit the push to level off and Not the alt button in the event of a need to level off ?

all thoughts welcome

:ok:

Dome Lighting in A320
 

FCOM 3.03.4 Preliminary cockpit preparation.

Dome lighting should be on because it is the only source of lighting in the EMERG ELEC configuration. The DIM position is recommended for take off.

After the BA/EZY Incidents
 

A320 family being modded to A330 status. i.e. dome light illuminates when on batteries only. So modded aircraft can take off with dome lights off.

Do not forget that when you activate the app phase, the FMGC computes speed at present weight (for ex 63.2 t) then when you do the go around, your weight will be different maybe 300 or 400 kgs depending when you activate the app phase. So your speed will be slighty different (1 or 2 kts) no more.
The other reason is that the value of S F O speed might be slightly different (for ex 1.22 to 1.25 of Vs) depending of phase

I am aware of the recommendation ie 'should' as opposed to 'must' re the dome light. However, I used to take off with the dome light off at night - always - for better night vision.

In any case, iirc, the dome light switch was easily found. I preferred to cater for the 99.999% rather than worry about a 0.5 second delay in the 0.001% case.

Fmgs a320 t/o shift
 

hi everyone
can anybody throw some light on why does T/o shift on perf take off page has a star next to it.

Hi Autopilot320,

Well no one could accuse you of not doing some research first.

With GPS primary position update, we normally leave the take off shift box blank.
Without GPS primary, we insert the published distance from full length to the intersection we are using to line up. When we set Take off Thrust, the FMGCs will then "position update" using those figures.

Pas vraiment la question...
 

[EDIT]You are quite correct but that was not the question asked.


Westinghouse, you're spot on for the F speed discrepancy between APPR and GO AROUND phase (F speed of GA phase being about 15 kts higher than the APPR one IIRC)
I personally don't have a definitive answer but as previously stated, I think this is the 14% increase mentioned in FCOM 3.4.10 p1.
If that is the case, when in CONF 3, your GA F speed should then be only 4% higher than your APPR one...
Without being absolutely sure, I think it has to do with approach and landing climb gradient/certification stuff...Sorry for not being more specific.

I think it is the fact that F speed is "about" 1.18 VS to 1.22 VS.

They don't explain why the non-exactitude of F speed, but I would say that is the reason.

As for Sebxl post, the FMGC calculates the speeds based on estimated landing weight until approach phase is activate, from which point actual GW is used. he is right, I htink

anyway, F speed will change at about 1 or 2 kt per ton, maximum. The difference for that reason should never be 15 kt!

Right, just found the reference ;)

The OP question was about the diff btw F speed on APPR and GA pages...not F speed before and after APPR phase activation.

On the A330 (don't remember on the A320), check your F speeds in cruise for APPR and GA page, you will see around 15 knot difference. If I am not mistaken, that's what the OP is asking about.

I thought it reflected the manoeuvre margin.
On the APPR we can use more than 15 degs bank,
on the GA it's assumed we'll limit the bank angle to 15 degs.