IRS mode panels

[Ka8 Flyer]

Something I've been wondering for a long time:

why do short to mid range (Boeing/Airbus) aircraft have IRS position entry panels on the overhead while their long range counterparts don't?

As an example:

B737 (NG and Classic with EFIS) are so equipped while the 744 only has the three IRS mode selectors.

A319/320/321 family has the equipment while the A340 doesn't.

What about the 767? I've seen both options there. Maybe something that has to do with age? (old ones not equipped while the new ones are equipped with it?)

Regards,

Mark

[Old Smokey]

In many of the later generation aircraft that you allude to, a great number of separate control panel functions, such as IRS position entry panels, have been incorporated into the FMC/FMS CDUs. Also in pre GPS/IRS times, the facility was required to update Inertial position if drifting excessively. This facility to allow Lat and Long insertion entry to the IRS still exists in the FMC/FMS, but is basically redundant due to GPS position updating.

On the B777 aircraft, even the PA is selectable on FMC CDU #3.

That's the quick and dirty answer, I'm sure that others will come up with better sharp pencil answers.

Best Regards,

Old Smokey