Hello NGX Pilots,

 

I am a little bit confused about how to setup a IAN approach with the NGX. I read the FCTM part about IAN and it seems rather straight forward but on the approach I am trying I can't manage to get this working properly.

 

I am trying to fly french airport Nantes LFRS VOR21 approach which course is slightly offset from runway heading. I checked the legs page to verify that there was a G/P embedded in the procedure and a MAxx waypoint. I wondered why the G/P is only on the last segment of the final approach as it is not what I understood from the manual. I set both NAV to VOR freq and both course to final approach course. When I was on the intercept heading, I pushed the APP button but the aircraft did not capture the correct course. Instead, it turned away from the final course and tried to capture a course that is on runway heading...

 

Could someone please help me about the procedure and correct me if I am doing something wrong?

 

Best regards,

 

Pierre

Did you intercept with HDG SEL or LNAV. IAN should work with either, but if in LNAV there might be some issues as LNAV in NGX seems to be a bit screwy at times. Try HDG SEL if you didn't already.

 

Another consideration is how you setup your latteral path for the incercept. If you are on an incercept heading (LNAV or HDG SEL) try setting up an intercept in the FMC by bringing the next waypoint on the final approach course to the top in the LEGS page and entering the final approach course in the INTC line on 6R. Checkout "Direct To and Intercept Course" in Chapt 11 of the FCOM1. It is crucial that you bring a waypoint up that will be ahead of you after your intended intercept point on the final approach course to the top, else you will be telling the aircraft to fly in another direction!

 

In real life, we would get the PM to do this. There is no standard call, just usually "Please extend the runway from XXXXX." Not to be confused with RWY EXT on the DEP/ARR Arrivals page!

I wondered why the G/P is only on the last segment of the final approach as it is not what I understood from the manual.

 

That's correct.

And IAN takes into consideration the final segment before RWxx waypoint for its profile. The whole G/P would be constant according to this leg.

 

tried to capture a course that is on runway heading

 

The same thing with FAC. Course between MA21 and RW21 here is 203 (despite the most of approach have 222*). This would be the course which IAN wants to intercept.

 

So better fly such offset approaches in LNAV or VOR with VNAV or V/S.

Thank you for your answers guys!

 

It makes perfect sense to me now.

 

I am going to try the "intercept course" function on my next flight as I had some problem to intercept the course coming from HDG SEL mode. That is exactly what I was looking to program^^

 

Regarding the final segment being the reference for the "virtual" ILS in IAN mode, you confirm it' s a limitation from NGX? I will now fly such offset approach in LNAV/VNAV and use IAN only when approach course is aligned with runway.

 

Best regards,

 

Pierre

Regarding the final segment being the reference for the "virtual" ILS in IAN mode, you confirm it' s a limitation from NGX?

It is not a real life limitation. Many VOR and NDB approaches are offset when the navaid is itself offset from the runway centre line, this is to ensure that the final segment takes you through the extended runway centre line to ensure an appropriate visual reference for manouvreing onto the runway centre line for landing. RNAV (non AR) approaches tend to be straight in.

 

Doing an offset approach IAN means that you will need to turn the aircraft when intercepting the extended centre line. This would normally be done only when visual by disconnecting AT and AP (PF) and resetting the flight directors (PM) (ir else they'll be commanding a different track). If you have FS2CREW, you can just callout "set flight directors off" followed by "set flight directors on".