by design Missed approach LNAV

[ShermheadRyder]

Hi,

I've seen an issue with lateral navigation on a missed approach, for example ILS 23R at EGCC.

The missed approach is straight ahead to 750' or D0.3 MCT, whichever is later, then right right to track 356.

However as you can see from the screenshot, the plane turns much further to the right than track 356. It appears to me as though the plane is computing the 356 track from the runway threshold (or similar) meaning it needs to turn far further right than track 356 in order to "capture" this path.

[richboy2307]

Hi @ShermheadRyder

Is this using Navigraph or Sim Default navdata?

[ShermheadRyder]

Just now, richboy2307 said:

Hi @ShermheadRyder

Is this using Navigraph or Sim Default navdata?

Apologies, forgot to include that in my original post - it was Navigraph data.

[richboy2307]

Ok we've checked, and in the navdata its only checking for 750ft before initiating the turn. There is no defined logic in the navdata itself to look for "750ft or D0.0 INN (D0.3 MCT) whichever is later" as charted. This would be an instance of pilot vigilance/checking required along with manual takeover in general. 

I have also attached my attempted missed approach, which clearly shows the aircraft maintaining runway track until passing 750ft, then initiating the turn after. The drawn 356 track is also visibly not starting from EGCC23R threshold (as if it were, it would have been much further right), but instead from computed VNAV path where 750ft would be satisfied.

If you also look closely in the video, you'll also note we have essentially satisfied the D0.3 MCT during the turn anyways and it is all well within the margins.

 

21 hours ago, ShermheadRyder said:

However as you can see from the screenshot, the plane turns much further to the right than track 356. It appears to me as though the plane is computing the 356 track from the runway threshold (or similar) meaning it needs to turn far further right than track 356 in order to "capture" this path.

In your case, as soon as EGCC23R was sequenced, and 750ft satisfied (if you were above it already), then the track to 356 got drawn, which is why the both seemed to coincide. But anyways, as mentioned, there is no distance check in the navdata itself, hence the drawn path. 

Thanks!

[ShermheadRyder]

Apologies for the false report, that makes sense - thanks a lot, appreciate it!

[richboy2307]

No worries, thanks for reporting anyways. I'll lock this now.