Reflectivity  This is a measurement of the ability of a target to 
Factor (Z)  reflect the energy from a radar beam. 
Relative  The bearing of a ground station relative to the direc 
Bearing  tion the aircraft nose points,or the direction of an air 
craft to or from an NDB. 
REL  Relative 
Resolution  A display indication given to the pilot recommending 
Advisory  a maneuver to increase vertical separation relative to 
an intruding aircraft. A resolution advisory is also clas 
sified as corrective or preventive. 
RET  (1) Rapid Exit Taxiway 
(2) Reliability Evaluation Test 
REU  Remote Electronics Unit 
RF  Radio Frequency. A general term for the range of fre-
quencies above 150 kHz,to the infra-red region (1012 
Hertz). 
RFI  Radio Frequency Interference 
RFP  Request For Proposal 
RFTP  Request For Technical Proposal 
RFU  Radio Frequency Unit 
RGCSP  Review of the General Concept of Separation Panel 
RIB  Right Inboard 
RIN  UK Royal Institute of Navigation 
RLS  (1) Remote Light Sensor 
(2) Reliable Link Source 
RLY  Relay 
R & M  Reliability and Maintainability 
RMI  Radio Magnetic Indicator 
RMP  Remote Maintenance Panel 
RMS  Root Mean Square 
RNAV  Random Navigation/Area Navigation 
RNG  Range 

RNGA  Range Arc 
RNP  Required Navigation Performance 
RO  Roll Out 
ROB  Right Outboard 
ROC  Rate Of Climb 
ROD  Rate of Descent 
ROI  Return On Investment