TOD calculation

[ahinterl 1]

This weekend I flew the ILS Z 24R approach into LEPA. From the attached image you can see that it's required to be at 3000 for a good while. Instead of using the AIRAC data, I fed the MCDU by hand and defined two PBD waypoints for "16 DME MJV" and FAP, both with an altitude constraint of 3000 ft. FAP has an altitude constraint of 2700 and was in my flightplan as PBD waypoint as well. The FMS constructed TOD to be approximately where the red triangle is in the image. I don't understand why it's there, is it because of the required switching to the approach phase so that the FMS would slow the plane once flaps would be set?Everything worked okay regarding the landing, but I'd like to know why the TOD was constructed this way.

[pixel9 0]

Hi, Andreas!Do you talk about having the TOD on this marked spot and descending from cruise altitude to the IAF from there? :( Just guessing, but this should've been like falling from sky, wasn't it?best regards,toby

[ahinterl 1]

Look at the image, you need to be at 3000 ft during almost the entire maneuver. My plane was at 3000 ft all the way into the turn. As said, there were 2 altitude constraints with 3000 ft set. To keep unwanted effects away, I let the alt window set to 3000 when the TOD was overflown. Since the FMA said HOLD 3000 in magenta with no other mode armed (and I didn't see the usual vert alert), I could imagine that the FMS wouldn't have initiated a descend even if the alt window were set to a lower altitude before TOD was passed.My question was that with the plane still cruising at 3000, why is the TOD where the FMS set it? My only guess is to allow for the "usual" automatic deceleration with flaps, i.e. approach mode is activated at a distance sufficient to allow for automatic deceleration using flaps (even for this, the TOD is set way too early, the plane can easily decelerate to even 160 kts before the turn towards the ILS is made...).

[Tigh 6]

Hi Andreas,That's an interesting one. How did you get down to 3,000ft, PROF or V/S? If it was V/S then if your previous waypoint had a restriction of 5,000ft then that might explain it.Otherwise, not sure.

[ahinterl 1]

I set crz alt to 3000. Maybe during hand flying I overshot to 3500 initially... The plane was at 3000 98% of the time, no waypoint alt constraint other than the two with 3000 ft were set...