A320 REC MAX FL

[matthewgamm]

Hello,

Couple of questions:

Does the fuel burn increase if we climb higher than OPT FL, say to the REC MAX FL.
If so, approx. how much is the increase?

Reason I ask is, at times, in the climb, our planned cruise FL is not available, and the choice now is between a lower FL or close to REC MAX.
In a situation like this, is it better to accept the lower FL and be stuck there for who knows how long, or accept the REC MAX FL.
Either way, I reckon that we'd be burning more fuel than what was planned for.
How do we go about making this decision?

Secondly, on a long trip, when updating the CRUISE winds, do we insert the winds for all the FL's above us, or 2 FL's above and 1 FL below, ...
What is the recommended way of going about this, to get the most accurate OPT FL?

Thanks.

[Airmann]

For fuel you are better off flying an equal distance higher rather than lower than OPT FL. That assumes all other things being equal, namely the winds. E.g. if you have to chose one FL above or below go above, it burns less.

However, as I said watch the winds. It's all about specific range at the end. The other consideration is the reduced margin between MMO and VLS (coffin corner), if it's going to be bumpy you should stay low and give yourself a better margin.

With regard MAX REC as you can see in the FCOM it gives you 0.3g margin. Technically you can fly higher, but it's not recommended unless you're sure it will be safe. And if you go above don't go over by more than a few hundred feet. Avoid it unless your sure of conditions and if the other alternatives are significantly worse off for your flight.

Also keep an eye on planned ISA and actual at the top of climb. If you take off from an airport with a high positive ISA then at top of climb if the ISA has decreased a recalculation by the FMS may result in REC MAX going up. So during climb expect this.

Lastly if you happen to fly longer distances over areas with significant changes in tropopause levels and therefore cruise temperatures, beware. An increase in temperature will obviously result in drops of both OPT and REC MAX.

[Amadis of Gaul]

Just do what the Captain says.

[FlightDetent]

Optimum FL is dependent on the speed chosen. You can watch it change as you go selected or modify the CI. REC MAX is perfectly safe, if you know what you are doing, and I think there's only one key point to it:

Make sure you have the correct temperatures inserted for the predictions to be valid.

Other than that, provided you have modern day wind data, I'd watch for wind component difference between the two non-optimal levels. If equal, my choice is to take the higher one. Apart from what had been said already, FL340 vs. FL380 makes for a significant difference in choices available if you need to deviate around TSs.

[sonicbum]

Hello,

Couple of questions:

Does the fuel burn increase if we climb higher than OPT FL, say to the REC MAX FL.
If so, approx. how much is the increase?

Reason I ask is, at times, in the climb, our planned cruise FL is not available, and the choice now is between a lower FL or close to REC MAX.
In a situation like this, is it better to accept the lower FL and be stuck there for who knows how long, or accept the REC MAX FL.
Either way, I reckon that we'd be burning more fuel than what was planned for.
How do we go about making this decision?

Secondly, on a long trip, when updating the CRUISE winds, do we insert the winds for all the FL's above us, or 2 FL's above and 1 FL below, ...
What is the recommended way of going about this, to get the most accurate OPT FL?

Thanks.
Hi,

Check FCTM NO-070-Step climb, that will give some food for thoughts. Other than that choosing a FL between your Opt and Rec Max can increase your trip burn up to 3%. Flying 4000 ft below your optimum can increase it up to 5%.

[vilas]

Matthew
You must go through at least once through Getting to grips with performance and FCTM.
Wind entries should be made for as many levels as possible to reflect the actual wind and temperature profile. This will ensure that the FMS fuel and time predictions are as accurate as possible and provide an accurate OPT FL computation. In cruise if wind difference is more than 30kt/30degrees modification at two flight levels 4000ft below and 4000ft above the current FL should be done. FMS creates a forecast model from pilot entered winds and a creates a predicted model by adjustment with current winds.
In GTG with PERF old figures for 320-232 specific range penalty for cruising at +2000 above optimum are 1.4% and 2000ft below 2.1%. Similarly - 4000 will be 6.2%. They are different for each model of A320.