Bug TU-204-100C

Hey,

i think this is a bug.

when i check dxb to cdg / lhr i can fly this route with 39% max load and 850km/h with no problem - if i change the speed to 851 / 849 or anything else it says not possible.

can someone from the support team check this please.

server is riem

If you check the aircraft performance tool, you'll see the plane is on the final downward slope, meaning it's already using its maximum fuel capacity and needs to drop seats/cargo to handle the trip. Any change to cruise speed will mean more fuel use than the plane can handle.

Yes, but a one knot change in speed should not require fuel equal to 39% of payload.

That's not a bug. But ...

If you check the Tu-154M KEF-DOH or the A320neo medium JFK-WAW, both planes will - just like the Tu-204-100C DXB-LHR - fly on full fuel load (volume-wise). So, decreasing/increasing speed will cause more fuel consumption on the whole run which can't be coped by putting more fuel in, obviously. The payload would at this point neither be restricted because it's all about volume limits. I guess the current calculations run into limits here?

Because the logic would dictate that now the range would just drop but maybe it can't? = This aircraft cannot operate the specified mission.

EDIT: Now that I am thinking about it... it kinda makes sense it can't... but I had a long day... :D

Run some "back of envelop" calculation and it seems like inconsistency in AS formulas.

For T20 DXB-LHR I'm getting consumption at about 7,5l/km. When checked T20 on DXB-LGG it seems that increasing speed to 851 lead to about 50l of additional consumption. Let's say that for DXB-LHR that will be 75 liters, so additional 10 km to fly.

When on second slope of payload-range curve we're shedding payload just to keep a/c lighter, so it use less fuel in initial phases of flight. That's sole source of range increase in that phase. Comparing T20 performance on DXB-LHR and DXB-EMA seems we're shedding some 3 tonnes of payload to gain nearly 90 km of range. At 850km/h for DXB-LHR T20 still has 11.7t of payload, so still plenty of range to shed for. Should be doable.

I think you should report issue to support, maybe adding some more examples/calculations.