STCA SOIR inhibit

Max Kuhla (1157125)

In preparation for EoR (Established on RNP) procedures at Arlanda we have set up as follows:

FINALAPP:ESSA:01L
FINALAPP:ESSA:19R
FINALAPP:ESSA:01R
FINALAPP:ESSA:19L
FINALAPP:ESSA:26
SOIR:ESSA:01L:01R:9.5:0.45:0.45
SOIR:ESSA:19L:19R:9.7:0.45:0.45

This should inhibit the STCA warnings for parallel approaches on 01L/R (01L on RNP APP, 01R on ILS) manually selected for the relevant aircraft.

In the RWY selection dialog only 01R is active for arrival.

It seems the SOIR/STCA inhibit only "lights up"/becomes active(?) when both 01L and 01R is selected as active (STS->Plugin status->STCA->View), not observing the selected runway for individual aircraft.

A chance of this behaviour would be critical for os to be able to implement the EoR changes having taken place at ESSA 6/10 IRL.
RWY 01R remains the active (main) arrival runway, and only select aircraft will be cleared for 01L, therefore only 01R will be the selected active in RWY selection dialog.

If I've misunderstood the logic, it possibly was caused by the aircraft on 01L not being within the NOZ for 01L yet.

As tonight progressed I created a custom curved NOZ for RWY 01L, but somehow the STCA alerts were not inhibited despite this.

SOIR:ESSA:01L:01R:9.5:0.45:0.45
NOZ1:N059.38.05.956:E017.55.39.529
NOZ1:N059.32.16.143:E017.53.32.744
NOZ1:N059.31.29.782:E017.52.31.019
NOZ1:N059.30.26.563:E017.50.32.575
NOZ1:N059.29.57.904:E017.47.57.430
NOZ1:N059.29.52.003:E017.44.38.911
NOZ1:N059.30.34.149:E017.37.56.868
NOZ1:N059.32.11.928:E017.38.41.910
NOZ1:N059.31.33.154:E017.44.42.247
NOZ1:N059.31.33.997:E017.46.37.355
NOZ1:N059.31.54.227:E017.48.45.809
NOZ1:N059.32.38.425:E017.50.23.348
NOZ1:N059.33.20.205:E017.51.52.650
NOZ1:N059.33.52.236:E017.52.19.342
NOZ1:N059.38.18.600:E017.53.52.762

Any ideas?

Juha Holopainen (839337)

The STCA inhibit for SOIR setups does not support curved approaches. The alert in the picture is caused by SAS having a greater than allowed ground track difference from the runway track, therefore the code expecting it to bust out of its NOZ. Possible workarounds would be

1) increase the allowed track error setting (STCA_NOZ_Delta_HDG) up to the maximum 90 degrees but that's a system-wide setting, reducing the effectiveness of STCA alerting for the straight-in approaches and the final straight part of the curved ones.

2) create an STCA inhibit area covering the curved part of the approach, and either make it always active, or activate manually when parallel approaches are being flown

Juha Holopainen (839337)

Regarding method (1) above, I'll look into making it possible to limit the delta_hdg check to only the final straight part of the approach by defining the straight part's length in the SOIR setup. This would keep the check working for the final straight segments. Modifying the track error check to work completely with curved approaches would probably be too much work.

Max Kuhla (1157125)

Thank you for your responses. We'll try a mix of the two methods!

Having an STCA inhibit area on the curved part, combined with defining the NOZ to only cover the straight part of the approach (allowing the track error tolerance to remain unchanged).