The other commentators are correct about the 5 by 5 part. I do believe the, 'in the pipe' part refers to being in transit to land. I heard the term originally from Pilots referring to the visualisation produced by the client end of a TLS (Transponder Landing System). The TLS largely automates that landing process.
Five by Five
The other commentators are correct about the 5 by 5 part. I do believe the, 'in the pipe' part refers to being in transit to land. I heard the term originally from Pilots referring to the visualisation produced by the client end of a TLS (Transponder Landing System). The TLS largely automates that landing process.