Gin
it refers to a radio fail procedure in which a pilot's original clearance is lower than the flight-planned one. Under RLCE (as it's written), after a radio failure, the Pilot has to leave controlled airspace, climb clear of said controlled airspace to the flight planned level, and then re-enter. This is different to "Climb when instructed by Radar" in which the Pilot can climb to the flight-planned level while staying within controlled airspace.
There are other technicalities such as squawking and maintaining present flight-plan for a set period of time, which I won't bore you with.
It is an anacronism from the days when no-one flew above 20,000' which haunts us still...which brings me to my next point...I've often wondered what would happen if the flight-planned level was above F245 (which it usually is nowadays)? How do you follow RLCE procedures and climb to a flight-planned level in Class B airspace which requires a clearance?
Any Area men/ladies or Pilots want to have a go at that one?
Tori