Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Boeing (744/8) Localizer "sensing"

Tech Log The very best in practical technical discussion on the web

Boeing (744/8) Localizer "sensing"

Old 9th Jun 2021, 00:33
  #1 (permalink)  
Thread Starter
Join Date: Mar 2011
Location: Earth
Posts: 136
Boeing (744/8) Localizer "sensing"



Is there any prohibition or harm in arming the LOC prior to having "correct sensing" i.e. when the localizer pointer is still sensing in reverse due to the aircraft not yet tracking within 120 degrees of the localizer course? Example being a Localizer approach with a procedure turn: should/may you arm localizer prior to the inbound portion of the procedure turn?

As I understand it, the aircraft will not inadvertently capture the backcourse. The systems manual states "localizer capture can occur when intercept track angle is within 120 degrees of the localizer course".

Additionally, the FCTM states:

APP mode should not be selected until:
-The ILS is tuned and identified
-The aircraft is on an inbound intercept heading
-Both localizer and glideslope pointers appear on the attitude display in the proper position
-Clearance for the approach has been recieved.

Notice it says "APP" mode, not "LOC" mode, although logically the implications would be the same for the LOC mode.

My apologies if I missed this answer elsewhere in the manuals.

Personally I don't arm the LOC or approach modes until I have correct sensing as a matter of airmanship but I hesitate to tell others to do the same without a reference. I am attempting to build a case to dissuade people from premature LOC selection during a non-ILS, but maybe I'm wrong about this.


Last edited by RandomPerson8008; 9th Jun 2021 at 01:09.
RandomPerson8008 is offline  
Old 9th Jun 2021, 07:40
  #2 (permalink)  
Join Date: Oct 2009
Location: Australia the Awesome
Posts: 321
C H I P s

The Boeing instructors on the 787 back in 2013 were big on:

C - Cleared

H - Heading to intercept

I - ILS on PFD

P - Pointers in correct sense

But I can't remember if it "HAD TO" be in the correct sense or whether it was just good airmanship.
Roj approved is offline  
Old 9th Jun 2021, 07:52
  #3 (permalink)  
Join Date: Sep 2011
Location: FL390
Posts: 110
I really wouldn't do it while the localiser is showing the wrong direction, if for no other reason that it might then not turn onto the inbound course when the pointer flips to the correct side. Or turn the long way around to the inbound course.
Fursty Ferret is offline  
Old 9th Jun 2021, 16:01
  #4 (permalink)  
Join Date: Oct 1999
Location: Up there
Posts: 187
You can arm and capture with incorrect sensing it will turn correctly.

However, I too wait for correct sensing though as usually it means Iím closer to the runway and less likely to suffer the following.

Flight crews should exercise caution to possible false capture of localizer and flight check procedures should be designed to reduce the risk of this type of event by not allowing the Flight Director/Autopilot capture modes to be armed too early.

CCA is offline  
Old 14th Jun 2021, 16:54
  #5 (permalink)  
Join Date: Sep 2002
Location: 8000 feet of cabin altitude
Posts: 535
Notice it says "APP" mode, not "LOC" mode, although logically the implications would be the same for the LOC mode.
I would argue the reason there’s a difference is if LOC captures the wrong localiser, you can engage another roll mode and recover.

If using APP and it locks onto the wrong ILS, you’d have to select TOGA or turn off the A/P and F/Ds and then rebuild, all while turning the wrong way, possibly towards hills. Bit messy.

speed freek is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.