Help understanding autorouter altitudes and speeds
So I just tried the autorouter for the first time to get a taste of what to expect and a few questions come to mind. I asked for a route from Wick, Scotland to Sabadell, Spain, something I may fly when I get my plane across the Atlantic. Here’s what I got:
EGPC N0125F040 WIK/N0131F110 DCT SMOKI/N0134F150 Y904 NANEV/N0137F190 Y904 ADN/N0139F220 DCT 5640N00201W DCT MADAD DCT 5507N00140W DCT NATEB P18 POL M605 WOD L612 BOGNA DCT SITET UN859 LOMRA UN727 ROCAN UN859 PUMAL B31 BERGA/N0136F170 B31 MAMUK/N0125F140 B31 SLL VFR LELL
The routing part (airways, DCTs, waypoints, etc) is clear but I’m confused about the altitudes and speeds. Or am I just supposed to submit the flight plan without the altitudes and speeds?
After takeoff I’m supposed to climb to 4000 and keep to 125kts? Doable, but am I supposed to do it before WIK? WIK is right over the airport. Doesn’t make sense to me.
Then after WIK climb to 11000 and speed 131kts? Doable, but do they really expect me to fly slower than my normal cruise speed? I’m usually at 175 true at that altitude. Are these speeds IAS or TAS?
Toward the end we have MAMUK/N0125F140 right before the destination. Am I supposed to get down from 14000 to surface in 8.3 miles? That’s pretty much a nosedive, not even possible with the gear and speedbreaks out.
What gives? :)
Speeds in flight plan are always TAS. The speeds on your route given by Autorouter depend on altitude, your plane performance and phase of flight.
If the distance primary chosen criterion then the route can have some “strange” altitudes defined by airways or MRVA or whatever criteria is applicable.
Practical advice: file this plan and during the flight nobody will expect you to do impossible things. I have never had any problem with any route generated with Autorouter. You can always expect that actual flight deviates from planned due to other traffic, weather, local rules, transiting different zones etc. but don’t bother yourself with that just file and fly.
I won’t be able to give you an answer as good and complete as Achim or Tom, but I’ll try to give you my version and maybe save them the effort.
AFAIU the altitudes are chosen to optimise the EET (or whatever optimisation target you chose in “advanced options” based on
In you aircraft model you have entered cruise speeds (TAS) for a set of different altitudes. If you have a turbocharged engine like it seems you do (lathough the speeds are low), the higher you fly, the faster. So the router may want a high altitude to reduce flight time. The altitude and speed are inter-dependent. According to the aircraft model, at a certain altitude you may achieve a certain speed for the power selected.
What goes for the route filed goes for the altitude too. Neither is entirely binding (unless NORDO). You can receive vectors or DCTs. So you should plan your descent based on your speed and desired rate of descent, and request clearance to descend. You may decide to remain at FL110 although you filed FL190 from NANEV.
You can manually edit your flight plan to modify the altitudes, but the flightplan may not validate after having done so especially because a portion of your flight is on upper airways available only above FL195. You may not change the speed. It will be computed according to your altitude and aircraft performance model.
One piece of advice though: do not file for an altitude you cannot achieve.
Although it is partly true that ATC does not care what speed you fly at (on lower airways – because the fast and furious ones fly higher), the autorouter uses your TAS (and forecast wind) to compute the PLOG and the EET which may be a factor if you are NORDO.
Most of those level and speed changes are fiction, to get around the computer algorithms in Eurocontrol 
When you fly IFR, normally you climb until you are VMC on top and you sit there in sunshine for the whole flight. Occassionally you don’t have the aircraft performance to out-climb IMC and then you can have problems.
In most of Europe there are minimum IFR levels, usually related to CAS base since you fly mostly in CAS. Practically speaking FL080 is the base in most of Europe. Some large city area transits are higher e.g. Frankfurt FL130 or so.
ATC doesn’t care what speed you fly at. That is just to get the FP into the validation system. Eurocontrol programmers get paid €0.34 per line of code so they generate lots of it! They have performance models for everything and you get something like a plus or minus 30% leeway (but AFAIK the actual margins are secret).
One unfortunate thing about the Autorouter is that you can’t change the speed (away from the predefined aircraft perf model) and this can cause problems in rare cases where you have to come up with an ETA which falls into a narrow time slot. The most notorious example is the annual show at EDNY where they will chuck out a flight plan whose ETA misses the booked slot. In that case I use a different FP filing agency e.g. EuroFPL which is my normal backup.
I don’t even look at the altitudes in the filed plan anymore. First of all (in Germany) you are almost always asked “what level you prefer” and depending on weather i will always ask for my preferred altitude/level.
If a certain altitude is not possible – they will tell you.
I just check the routing. But even that is fiction. Two days ago i got a 250 NM “Direct to Destination” between Paris and Munich.
Peter wrote:
One unfortunate thing about the Autorouter is that you can’t change the speed (away from the predefined aircraft perf model) and this can cause problems in rare cases where you have to come up with an ETA which falls into a narrow time slot. The most notorious example is the annual show at EDNY where they will chuck out a flight plan whose ETA misses the booked slot. In that case I use a different FP filing agency e.g. EuroFPL which is my normal backup.
Why would you want to change the speed? It is picked from the airplane performance model according to your chosen altitude. If your aircraft model is correct, i.e. you have created it yourself or tweaked a pre-existing model, and you enter your desired altitude into your flightplan, your speed is correct. In addition you can enter your climb and descent speeds.
The speeds for my airplane are spot on for any altitude between ground and FL190 and the PLOG EETs are within a few minutes of reality modulo shortcuts and wind. The one thing I wish I knew how to tweak is taxi/run-up time.
It is not always fiction though! You do have to be able to fly the filed route because sometimes you have to.
Alexis wrote:
Two days ago i got a 250 NM “Direct to Destination” between Paris and Munich.
That’s very often in Germany in my experience – the other day I got direct from Luebeck to Hermsdorf. Austria and Hungary implemented direct routes if you overfly, in Croatia and Slovenia you always get it if traffic permits.
Alexis wrote:
I just check the routing. But even that is fiction.
You are right in that point. But keep in mind that in the standard way one need to enter all the waypoints generated by the Autorouter into the GPS (KLN94 in my plane), which often means zigzagging. Sometimes I get more than 25 waypoints, which is the limit for my GPS. In order to get a better routing I try to get shortcuts by choosing a higher Flight Level via the advanced options which sometimes gets me an even worse routing.
Aviathor wrote:
If you have a turbocharged engine like it seems you do, the higher you fly, the faster. So the router may want a high altitude to reduce flight time.
Peter wrote:
You do have to be able to fly the filed route because sometimes you have to.
This is the reason why I normally do enter all the waypoints into the GPS. But often it is more practical to enter just the first waypoint on a Z-plan, since many times one get different waypoints or good directs from the beginning. Even the SID changes often once airborn.
highflyer wrote:
This is not working for me. I always get lower Flight Levels like FL 090. I did ask Achim in this matter and surprisingly got the info that my performance data are wrong.
I had a max FL in my model and had the same problem. Change it and autorouter will give you higher levels.
