Originally Posted by
Airmann
Just remember that once issued a block altitude all calls to ATC must state the block that you are maintaing, with no reference to your current altitude.
I read recently about the potential of both block altitude and cruise climb availability over the Atlantic. However, given the level of traffic I haven't even dared to ask. Has anyone here done so?
And with regard to cruise climb, I understand that the basic difference between it and a block altitude is that in the former once you climb you can never descend, but are there any other differences?
Cruise climb causes considerable consternation with some air traffic service providers and the ICAO Global Operational Data Link document (GOLD) repeatedly warns:
Note.— Avoid use of this message element due to potential misinterpretation
The idea with a cruise climb is to set engines to the most efficient power setting then instead of maintaining level just allow the aircraft to climb as weight reduces. The issues are that if the outside air temperature warms then (due to the thermodynamics of the engines) the aircraft will lose power and descend. Hence the warning that the aircraft should not be allowed to descend, but to stop that means adjusting engine power so defeats some of the object. This is the reason for allocation of a Block [bottom] to [top] as the aircraft is only required to stay in the block and can be separated from other aircraft. Of course it also means that you have just been allocated a huge chunk of airspace. As normally the block starts at one waypoint and extends to another.
As ATM tools improve they are becoming more capable of deconflicting aircraft on cruise climb and some authorities namely NAV Canada are more approachable on cruise climb than others some will not even countenance the idea. So that is why aircraft are given step climbs that approximate to a cruise climb but in a series of level segments. Not ideal as the engines are required to accelerate to climb power for the climb between level segments and are really only at maximum efficiency for part of each level cruise leg. [Note that when looking at the efficiency of cruise climb you need to include the potential energy gained over the cruise climb duration and its release as kinetic energy in the descent. Do not just look at the fuel flow during the cruise climb.]
As more airspace becomes 'free route' and allows 'business trajectories' that do not follow route structures (. e.g the North Atlantic OTS is due to disappear very soon.) expect the support tools for the controllers to be improved so the procedural block clearances will become less necessary. So brush up on engine performance in the cruise you can save a lot of fuel.