View Full Version : 737 OHD Systems basic IRS logic

05-29-2008, 05:25 AM
Somebody in another thread asked me about transplanting the IRS function from the 747 overhead logics to the 737 overhead logics.<o =""></o><o =""></o>
Here’s what I did.<o =""></o>
<o =""></o>First, in the 737 graphics, I converted the DispSource knob to be the IRSSelector1 knob by simply renaming it. I kept the old line as a remark for backup sake. Here’s what I added:<o =""></o>
<o =""></o>
//element knob3,-184.8,-44.0,DispSource<o =""></o>
element knob3,-184.8,-44.0,IRSSelector1<o =""></o>
<o =""></o>
You may wanna additionally play with the “text” instructions around the knob and re-label them according to the three IRS knob positions (OFF – ALIGN – NAV), which have logic values of 0, 1 and 2.<o =""></o>
<o =""></o>
Then, in the 737 logics:<o =""></o>
<o =""></o>- in the [consts] section, I added one line for the timer duration:<o =""></o>
irstimer = 1200<o =""></o>
(where this value is equivalent to the standard 10 mins. of a full alignment cycle).<o =""></o><o =""></o>
- in the [logics] section, I added these lines, grossly taken from the 747 Systems:<o =""></o>
<o =""></o>if IRSSelector1=0 then<o =""></o>
IRSAligned1=0 <o =""></o>
endif<o =""></o>
<o =""></o>
if ((IRSSelector1=2) or (IRSSelector1=1)) then<o =""></o>
IRSAligned1 = counter irstimer 2<o =""></o>
endif<o =""></o>
<o =""></o>
if (IRSSelector1=1) and (IRSAligned1 = irstimer) then<o =""></o>
IRSAligned1=irstimer - 2<o =""></o>
endif<o =""></o>
<o =""></o>
if (IRSAligned1 >= irstimer) then<o =""></o>
IRSNotAligned = 0<o =""></o>
else<o =""></o>
IRSNotAligned = 1<o =""></o>
endif<o =""></o>
<o =""></o>
Take it as it is, a basic inspiration; I am aware that this is not the full logic, and that it is based on a single IRS System, but it does anyway give you something to do about IRS when you’re setting up the cockpit before departure … any suggestion, correction, further development is absolutely welcome.

Have fun !!!
<o ="">

05-30-2008, 04:55 AM
737 users know that the IRS System has two knobs, with four positions each: OFF - ALIGN - NAV - ATT

I had forgotten one, sorry !


Paul G
05-30-2008, 05:54 AM
What's a knob or two, among friends?!

05-30-2008, 08:04 AM
Hey there Paul ...

maybe you meant "what are three positions or four, among friends ?" ... ?


06-06-2008, 12:51 PM

just to add my 2 cts worth idea: have you ever tried Thomas Richter´s very neat program called "Cockpit Systems B737" yet?
There you can find also the IRS part with offsets for the 2 kobs.
It´s really worth buying it. No messing around with offsets anymore as the entire overhead can be tested.

Best regards


06-09-2008, 03:42 AM
... I've recently bought Thomas' 737NG, and am now focused on the Autoflight Annunciators function.

Having no physical overhead (I keep PMSystems on a flat display hanging over the pedestal, coupled with a few GoFlight modules), I must depend on the graphic development of PMSystems.

Thanks for the suggestion, anyway !