PFRX means Preflight Relmat
X-1,2,3...9 or A,B,C...Z in
NASA
Similar to PFRX
A/L - Approach and Landing
AA - Astronomical Applications
AA - Adverse Action
AA - Antenna Assembly
AAA - Avionics Air Assembly
AAC - Aft Access Closure
AACB - Aeronautics and Astronautics Coordinating Board
View all in NASA