The RC-26B fleet (6 x Block 25R + 5 x Block 20) is currently in severe danger of not meeting mission requirements due to an antiquated avionics suite.  As of now, NGB has funded only the Block 25R's to receive avionics modernization upgrades, although the Block 25R fleet is still 2 years removed from full implementation & fielding of the upgrades.  If the Block 20's are not funded for and implemented with a modernized avionics suite, they will begin to be grounded within the next calendar year due to non-compliance with  air worthiness directives.    This is based on extensive statistical analysis from the System program Office (SPO) and Contractor Logistics Support (CLS) data.  Critical parts are no longer manufactured and are no longer serviceable for reconditioning.  The remainder of the avionics suite is at the end of its service life, does not meet FAA 2020 requirements, and is currently incapable of using GPS as the sole source of navigation.  The RC-26B is not worldwide deployable in its present state.  Current avionics parts can't be upgraded to meet any of these requirements without wholesale replacement due to age & diminishing manufacturing sources and Original Equipment Manufacturer (OEM) vendor support.   The currently-funded Block 25R avionics suite upgrade IS COMPATIBLE with Block 20's.  Additionally, the Block 20's have yet to incorporate the upgraded FLIR 380HD sensor turrets, even though they were purchased in 2013 and interchangeable with the Block 25 aircraft.  The FLIR 380HD sensor is a significant increase in capability for the Block 20, with minimal engineering required for fitment.