Airbus PPOS

[saviboy]

Hi Everyone

I know the subject has been brought up several times and though I found some good info using the search function, I still need some clarification
Here's what I think is correct:
1) in order to get PPOS, one needs to fly into a discontinuity.
2) if one clears the to waypoint while in heading, PPOS becomes the From waypoint .is that correct?
3) there is a scenario that is often used as an example to explain the need to keep PPOS as the from waypoint: you are flying wihtin 5nm of the runway (E.g: Abeam the airport) or overflying it. If you don't keep PPOS, the flight plan will disappear as the plane thinks the plane has landed.
can somebody please explain that properly?
Does it matter which point is the TO waypoint? Can it be the FAF for this to happen? The runway itself?

Finally, if there are any other rule that any Airbus pilot should know regarding PPOS, I'd apreapprec it if you could list it along with the FCOM/FCTM reference so I can look it up.

Thank you

[Pugilistic Animus]

I don't understand anything about these Airbusses

[pineteam]

Hello,

Talking about the Thales FMGC.

1:Yes
2:Yes
3: I heard that story too. Some colleagues told me it happened in the past. But I don't understand how technically it's possible. For the FMGC to switch from ''Approach phase'' to ''Done'' the condition is that the aircraft must be on the ground for 30 seconds. FCOM- Aircraft Systems- Auto Flight- Flight Management- Flight Planning- Vertical Functions

For the Tips in general, I recommend you download the '' Thales New FM Pilot guide book'' available for free on Smartcockpit. You have extra information about the FMGC that you won't find in the FCOM.

Cheers.

[vilas]

Done phase and flight plan disappearing are two different things. If you overfly the destination it will get sequenced and the flight plan will disappear. You will have to create direct to, lateral revision and reselct what is required. Transition to done phase will only occur after landing on ground. Where FMS will be availablel the usual way for programming the next sector.

[pineteam]

Thank you for the clarification Vilas.

[PENKO]

Vilas, out of curiosity, the airbus logic regarding overflying of destination seems to have changed somewhat, either that or my memory is playing tricks! There used to be a reference in my OMB, indeed stating that overflying the runway would sequence the destination and erase the flight plan. That reference is there no longer.

Airbus now states more or less the following (full reference:22_20-30-10), depending on FMGC model, either:

-sequencing is inhibited unless XTK <.5 NM and <30 degree track difference between aircraft and leg
-waypoint is sequenced when <7 NM and track <90 degrees

Both suggest that Airbus have addressed the issue since merely overflying the destination will now not normally erase the flight plan. Please correct my if I'm wrong, I'm still tryingto work it out.

[vilas]

Hi Penko
You are right. Airbus has made conditional change for sequencing the destination. The latest one has the following:
Note: 1. When the aircraft overflies a flight plan discontinuity, the NAV mode automatically reverts
to the HDG (TRK) mode.
2. In HDG/TRK mode, a waypoint is sequenced when it passes behind the aircraft, and the
aircraft is less than 5 NM from it. In addition, when the waypoint is the Destination Airport
(DEST), the sequencing is inhibited, unless the following conditions are fulfilled within the
3 s following the general rules fulfilment:
‐ The cross-track is less than 0.5 NM
‐ The difference between the track of the aircraft and the track of the leg is less than
30 °.
The same conditions apply in NAV mode, except that no distance to the waypoint is
taken into account.
EARLIER FCOM was as follows:
Note: 1. When the aircraft overflies a flight plan discontinuity, the NAV mode automatically reverts
to the HDG (TRK) mode.
2. In HDG/TRK mode, a waypoint is sequenced when it passes behind the aircraft, and the
aircraft is less than 7 nm from it, and also when the difference between the track of the
aircraft and the track of the leg is less than 90 °.
If the aircraft is flying a discontinuity towards a waypoint, this waypoint is sequenced
when the aircraft is less than 5 nm from it.
The same conditions apply in NAV mode, except that no distance to the waypoint is
taken into account

[pineteam]

Interesting that in our latest FCOM we still have both notes. The latest one for all the aircraft equipped with Thalès FMS and the old note without conditional change for an old bird (MSN 908) equipped with an Honeywell Legacy FMS. It was our last aircraft equipped with very old Honeywell FMS. It was sent to the desert last year.

[Escape Path]

I remember this scenario (fpl deleted) is most common when one is not flying a "conventional" procedure. This is usually setting up a visual traffic pattern (or visual approach, whatever it might be), which has no missed approach procedure, hence no more waypoints after dest. To prevent fpl deletion we manually insert a waypoint after dest that is coherent with the intended flight path in case we go around. You will have a fpl so long as you don't sequence all waypoints in it

[saviboy]

Thannks for the replies everyone.
I would need clarification about the following:

1) "If the aircraft is flying a discontinuity towards a waypoint, this waypoint is sequenced
when the aircraft is less than 5 nm from it."

That means that if I'm on the base leg, in HDG, PPOS as the FROM waypoint the way point will sequence out automically as I get within 5nm?
I was always under the impression that one would carry PPOS inorder to avoid exactly that .What am I missing?


2) "The same conditions apply in NAV mode, except that no distance to the waypoint is
taken into account"

For example: I'm in NAV direct to the IAF. As I reach the next fix, eg: the FAF, the runway becomes to the TO waypoint .is that what is implied?

[vilas]

That means that if I'm on the base leg, in HDG, PPOS on top of my flight plan PPOS is from way point.

[saviboy]

PPOS is from way point.
thanks. edited my last post for correction.