Missed APPs - Wrong Direction of Turn?

[NoslenYL]

Noticed that on a few missed approaches the FMS path doesn't quite match up with the missed approach instructions on the chart. An example would be the ILS 25L into KLAS, where the missed APP commands a climb to 3100 before turning right* direct BLD VORTAC and continue climbing in hold to 7000. But the FMS 1) shows a left turn and 2) the flight path has a "kink" in it instead of just going direct BLD?

KLAS ILS 25L - https://skyvector.com/files/tpp/1607/pdf/00662IL25L.PDF

Not sure if this is a bug or something also present on the real plane (ie the database doesn't have info about "direction" of turn, only the waypoints), in which case I'm assuming LNAV isn't used for missed APPs?

[Litjan]

Yeah, this is due to the way we calculate the "runway centerline" - sometimes the resulting number differs a bit - don´t let it throw you off, the succession of waypoints it the accurate line...

Jan

 

[NoslenYL]

Feeling a tad bit clueless here, but I'm not sure I understand :/ Think I get the runway centerline causing the "kink" that isn't actually flown, just confused still on the direction of the turn. Is that also because of the centerline?

[Litjan]

The "kink" is the attempt of the FMS to re-intercept the direct line between the initiation of the turn and the target waypoint. I don´t know the description of the MAP, but it could be that the bearing inbound to the holding fix could be specified.

Jan

 

[Jojo38000]

Hi,

From what I understood in Tom's previous posts on a similar "issue" and from my own experience using this bird, the direct to will make you go to the waypoint by intercepting the "line" "position twhen the direct was initiated" - "targeted waypoint".

You can see a similar issue at KLAS, on the BOACH6 departure, runways 01. You will have the same kink instead of a "true" direct to. (A saw a topic on this not long ago)

From what I remember Tom stated that this portion of the code needs tweaking, not sure though, could be working as designed since the beginning.

 

Cheers,

Jonathan 

Edited June 25, 2016 by Jojo38000