First of all, thanks a lot for the recent features and updates released!
This is perhaps more of a discussion, but I find that when Simbrief calculates based on optimum flight level, especially with 777F (which I fly most of the time), it often calculates an initial cruise that is below RVSM (<FL290).
While technically probably valid and optimum, I’d think that real dispatch systems would rarely do that (not in aviation myself, so free to be corrected) for operational/ATC reasons. Most of the time VATSIM controllers also ask me to adjust the filed altitude to FL290+, if I hadn’t changed it from Simbrief’s already.
Another related issue is really early step climbs; it’ll add a step climb at a waypoint where I’m still in the climb to my initial, or maybe just reached it; so initial filed could have been the higher altitude. Example for that below (S/C at ZUH);
Yes, this is correct. You are almost at MTOW for this flight, a B77F simply cannot cruise above FL290 at MTOW.
In fact, the optimum altitude at MTOW is around FL275 at MTOW, and the max altitude somewhere in the range of FL280-FL300. But SimBrief will never plan you right at the max altitude, because it is both inefficient and also leaves too little margin.
This is exacerbated by the use of metric flight levels in China. On your initial airways, you have the choice between FL276 (8,400m) and FL301 (9,200m). If for whatever reason you are too heavy for FL301, your next choice is FL276.
And on this particular flight, SimBrief also planned you a bit lower than normal due to winds it looks like.
I am not aware of any such requirements. If anything, cruising outside of RVSM is less restrictive (requires less equipment and procedures). I’m not sure why ATC would want to force you into RVSM, but every part of the world has their own procedures I suppose.
SimBrief in general tries to be conservative and gives you a bit more margin, but if ATC asks you to climb higher, simply check your FMS max/opt altitude. If you can climb, and are comfortable doing so, then do it. Otherwise tell them you are unable. You don’t need to follow the flight plan exactly, as the pilot you are free to deviate as needed once airborne.
This can happen for any number of reasons. Normally a step climb close to your top of climb is due to an airway restriction or direction change. In this case, you turn from east to west at ZUH, so you have to change altitude after this point. If for some reason you take longer to climb (due to ATC vectoring, restrictions, different weather than forecast, etc), then yes, you could still be in climb when you reach this point.
This discrepancy can also happen with real-world flight plans and is just a reality of flight planning. Flight plans are just a plan, not a crystal ball. Most real-world flights deviate from their plan in some way, and this is even more true in the simulator world, where it is often difficult to replicate real-world aircraft performance exactly in the sim.
If you haven’t reached your TOC yet, then simply request the next altitude right away. Or wait for ATC to assign you a different flight level.
I dispatch the real world 777F at work. All depends on the gross weight - if you’re trying to get to FL350 taking off at 766.0, not going to happen optimally. For example, taking off at 766, your optimum altitude is 28200ft. You can get to FL340 taking off at 766.0, but you’re going to burn a few tons more fuel. At 766, your fuel to climb to FL280 (optimum altitude for TOW) is 12.5, but 16.8 to get to FL340, all weights in lbs)
Specfiically for ops in Chinese airspace, I never plan an optimizing step climb as they arent guaranteed. I was in the cockpit JS a while back on a flight from NRT-CDG, we entered Chinese airspace at AGAVO, and we we’re exiting at SARIN. Underneath us was a KLM 777 NRT-AMS. As we were handed off to the various controllers the KLM guy was asking for higher, “unable traffic” was the terse response from ATC. I could see him directly underneath and on TCAS as it was a gorgeous day and his Blue fuselage was contrasting against the clouds below us. Once we were both NW of Beijing, he was able to get his climb as we were heading to different exits from their airspace. There is almost no flexibility in the airspace, so I accomodate that by being more conservative than other places in the world in my fuel planning.
So for example if I am entering Chinese airspace on a Europe-Tokyo at SARIN at FL331, I’m exiting at AGAVO at FL331. Obviously if the airway changes direction, I’ll plan the flight to follow. If the crew asks for higher and is cleared for it - great, but they’ll have the gas for when it isnt approved.
Some European operators have their FPS set to also not plan for optimizing step climbs in their airspace - they can set it by the FIR. At work we’d also be using a fuel rule that has just a 45 minute final reserve for a ZGGG-OMDW, no enroute required contingency fuel, but I’ll add 15 or so minutes “for ATC”, so I’m not dragging a bunch of unnecessary fuel along.
-K0922S0980 VIBOS R473 ZUH R200 LH R339 BSE A599 LINSO. Once past LINSO I’ll let it go to optimum altitudes again as the ATCs are now much more flexible.
Thanks for the response! Not sure where you got from that I was close to MTOW - this flight was at 706.7. Unless that’s considered close to MTOW already? FMS said opt was FL310 iirc. I S/C’d later to FL340 closer to OMDW, recommended alt by the FMS (causing +2min ETA but ~1t fuel save)
Regarding your other points - thanks for the clarification/info on that, you learn more every day!
Thanks so much for the info as well @dougsnow , that’s cool to hear!
