How do you change flight level enroute in your IFR flight plan?
I would like to file a FP starting with a low FL and go higher only where it is required on the airway. I tried adding Fxxx words in the FP but autorouter generates an error.
Choose the waypoint where you want to change FL and affix the new speed and FL.
For example, you’re inbound to RESMI in France and you intend to accelerate TO 450 Kts and climb to FL410 at that point. Within the route text you’d input….
RESMI/N0450F410
Thank you!
Has to be said that nearly all level and speed changes on an IFR FP are done just to get Eurocontrol validation. They are rarely if ever actually flown (ATC don’t usually care, and in some cases e.g. the UK they don’t see them; due to poor software they see just the initial filed level) and the speed is meaningless anyway because at European IFR altitudes (generally above FL070) one is flying at max available power anyway. You have to file roughly the right speed to get validation against Eurocontrol’s secret internal performance model for your type.
In Europe one tends to file for FL100 everywhere and increase that for the Alps 
Peter wrote:
the speed is meaningless anyway
That depends on what you mean by “meaningless”. In a procedural control environment, that information is vital to ATC and must be accurate. (Or you have to report the actual speed by radio.) Fortunately procedural enroute control is very unusual in Europe.
Just as well since GA can’t control speed; one flies at what the plane will manage at altitude x
Peter wrote:
They are rarely if ever actually flown
Some airways have high minimum FL. Do you mean I could file a FP with a minimum FL of, say 150, and then fly it at FL110 ?
Not unless you cancel IFR for that part, and even then obviously not physically (into a mountain).
Some of my Swiss flying videos are fun
No, because you are not then flying the airway.
The minimum altitude set on an airway can have several reasons. One is MEA, others depend on whether or not you can be seen on radar, or radio signals, both nav and or comms.
However, you don’t always have to fly the airways to fly IFR, just like in some countries you can fly airways VFR.
Peter wrote:
Just as well since GA can’t control speed; one flies at what the plane will manage at altitude x
Really? The POH has a performance section. In my experience the actual TAS is well within 5% of what that section tells you. (5% is the allowed tolerance on flight planned TAS under procedural control.)
