Yes, this is true - they are commodies. But, here's the rub. The Gov't runs off Technical Orders (TO's). The TO has a parts list, a drawing of the board, in some cases the schematic as well as maintenance, testing, calibaration and operational guidelines. Each piece of equipment may have a thousand page TO tied to it. So, if a resistor goes obsolete - now you need to change the TO on thousands of components (in which each obsoletel resistor was used) not only across our military/govermental operaions, but also across the TO's owned by our allies. Do you have any idea how expensive it is to republish a gazillion TO's in multiple languages?
Take the humble Carbon Composition resistor. Used to be common as dirt, now they are exceeded in precision by many other technologies - however the Carbon Comp is like a pinch of playdoh - it has thermal mass to it. Unlike film resistors which have an incredably thin film of resistive material, Carbon Composite can withstand significantly larger amounts of inrush current that would destroy a film resistor. Now, does the application in which this resistor is used require the large "in-rush" capability?
It's an unholy mess. And we are flying aircraft that will be nearly 100 years old before they are retired (as in the B-52).
Thank you for explanation. Didn’t know about different types of resistors; I thought a resistor had an ohm value and that was it... I guess they need to a surge protector or “leveler” or something in front of the film resistors...
“And we are flying aircraft that will be nearly 100 years old before they are retired (as in the B-52).”
Takes your breath away, that somebody could build an airplane like that. It would be like the HMS Iron Duke serving in the Falklands... Sad truth is, I think a C-130 could do much of the job of a B-52 today (just roll the bombs out the back...). I suspect the B-52 would have a very short life expectancy in a contested airspace.