"Steven P. McNicoll" wrote:

wrote in message ...

He did not say that right. There is VOR/DME-RNAV as well as
INS RNAV, IRS RNAV, GPS RNAV, and LORAN RNAV.


IRS RNAV?

Not in the airplanes you fly, Steve. In the big ships, three IRUs that
provide the attitude platform and the basic inertial reference. If the GPS
failes, the DME/DME fails, the VOR/DME fails, and the VOR/VOR fails then a
slightly degraded, but noneless very good position is provided by the IRUs
via the FMS, which in combination is known as the IRS (inertial reference
system), which in turn is IRS RNAV when all external sensors are not
available.