ETP (Equi Time Point to my generation) - the point
at which to go on takes the same time as to return,
usually all engines operating.
PNR - the furthest point at which one can return with
mandatory fuel reserves intact. This can be all eng, or
eng(s) out, or depressurised all engines operating. The
DPNR was usually the more limiting fuel on long ocean
crossings than PNR3 on the Whale. So if you carried
enough gas to cover DPNR then you were automatically
covered for PNR3.
I recall my Oz SCPL Flt Planning days where ETP and
PNR were mixed up together in the sub-subject of Base
To Remote Strips. I could never get my head around it
and knew I'd lose 10 marks or so if it showed up in the
exam. Fortunately the pass mark was 70%.