Definition
The fourth generation of GPS satellites operated by the United States, launched between 2010 and 2016 to replace aging earlier-generation satellites in the GPS constellation. Block IIF satellites added a third civil signal (L5) intended for safety-of-life applications such as aviation, improved accuracy, longer design life (about 12 years), and more accurate onboard atomic clocks compared to earlier blocks.
Plain English
A specific generation of GPS satellites that orbit the Earth and broadcast signals your GPS receiver uses to figure out where you are. The 'IIF' (two-F) just identifies which production batch they belong to.
Context Anchor
Seen in instrument flying material when the handbook explains the space-based part of GPS and how GPS capability has improved over different satellite generations.
Derivation
Block' is the U.S. military term for a production batch of satellites built to a common design. 'II' (Roman numeral two) marks the second-generation family of operational GPS satellites, and 'F' stands for 'Follow-on,' meaning these were a continuation of the Block II family with upgraded capabilities.
Why Pilots Care
They improve signal availability and accuracy for instrument approaches and reduce vulnerability to interference.
Intuition Check
Do not read “Block” as a physical block or an area of airspace here. In this context, it means a version group of GPS satellites.
Example Sentence 1
The Block IIF satellites broadcast the new L5 signal, which improves GPS performance for aviation users.
Example Sentence 2
Block IIF satellites provide the L5 signal that supports more precise vertical guidance on approaches.