# Thread: 737 OHD Systems basic IRS logic

1. ## 737 OHD Systems basic IRS logic

Somebody in another thread asked me about transplanting the IRS function from the 747 overhead logics to the 737 overhead logics.
Here’s what I did.
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:

//element knob3,-184.8,-44.0,DispSource

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.

Then, in the 737 logics:
- in the [consts] section, I added one line for the timer duration:
irstimer = 1200
(where this value is equivalent to the standard 10 mins. of a full alignment cycle).
- in the [logics] section, I added these lines, grossly taken from the 747 Systems:
IRSAligned1=0
endif

IRSAligned1 = counter irstimer 2
endif

if (IRSSelector1=1) and (IRSAligned1 = irstimer) then
IRSAligned1=irstimer - 2
endif

if (IRSAligned1 >= irstimer) then
IRSNotAligned = 0
else
IRSNotAligned = 1
endif

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 !!!

2. ## To be precise ...

737 users know that the IRS System has two knobs, with four positions each: OFF - ALIGN - NAV - ATT

I had forgotten one, sorry !

3. What's a knob or two, among friends?!

4. Hey there Paul ...

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

5. Hi,

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

Peter

6. ## Yes ...

... 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 !