ILS Frequency Tune - Automatic

[bob34 124]

Contrary to proper procedure, on my approach to KIAD 19C today, I clicked the APP button without putting the frequencies in the nav1 and nav2 radio and the localizer and glideslope came to life on the PFD. It showed the DME / Course and Freq for the 19C ILS. I had done this one time previously by mistake and the results were the same - a valid loc/gs 

Granted it was a single AP no auto-land setup, but I thought the FMC wasn't linked to any radios in the NGX.  Frequncy for that runway is 111.70 and nav 1 was 110.6 and nav 2 was 113.8.

From a systems standpoint (rather than procedural), can someone explain how the proper glideslope and localizer came to life upon pressing the APP button w/out the nav radios tuned? Is there a radio somewhere tuned by the FMC or Autopilot? 

[downscc 1,327]

Not that I am aware of... there isn't even a radio page in the FMS.  I haven't seen anyone reporting this happening in the past five plus years the product has been out. Interesting.  Was the cat nearby?

[JoeDiamond 67]

What did the FMA say?  Sounds like you were using integrated approach navigation.  The 737 does not have any auto tune capability.

[spesimen 135]

maybe another addon did it? for example, i think pro-atc has a setting that will have the co-pilot automatically tune the nav radios..

cheers,-andy crosby

 

[bob34 124]

Not sure how well you can see this, but the ILS is tuned on the PFD but the nav radios are not set to the ILS.

The diamonds change from white to pink when closer, just as the nav radios would do.

I can only assume the FMC interacts with the PFD and the ILS freq somehow. 

 

[Mike777 163]

Looks like you are flying an IAN approach.  FMA is indicating FAC for lateral mode and GP for vertical, as corresponds to this type of approach.  Haven't tried it yet myself.

See this thread, especially Tabs.

https://www.avsim.com/forums/topic/348034-ian-approach/

Mike

 

[Budbud 227]

Hi,

What is displayed on the FMA isFAC - G/P, which indicates an IAN mode which is an ILS-like approach mode but based on GNSS and not ILS.

If you were receiving an ILS signal you would see LOC - G/S displayed.

Have a look here: 

And there:

http://www.boeing.com/commercial/aeromagazine/aero_22/737approach_story.html

[bob34 124]

Mike and Romain. Thank you!

[Budbud 227]

You are welcome!

[Mike777 163]

Happy to help!  I learned something about IAN approaches by researching this.

 

Mike