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Daniel choen

climb thrust and thrust settings.

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Hello my simmers fellows,

i would like to ask about climb thrust, so basically, what does it mean and how do i perform that? is it on VNAV? is it level change?

my second question is, how do the pilot sets a DT on the 737? i mean there's no EFB and you know the precise weight only couple of minutes before pushback, so how it goes? thanks!

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Guest BeaverDriver

On Climb Thrust, I'd just let your Autothrottle handle this. Once you have hit your TO/GA button, everything after that should be automatic. The computer will determine how much thrust you need based on your flight profile.

 

Like Matt though, I don't know what "DT" means. You should know your weight well in advance of a couple of minutes though. Yes, if you are running your APU, some fuel will be eaten, but not that huge an amount. If you are referring to your V Speeds, those too are calculated for you by the FMC assuming you've programmed it (and this isn't an airplane that you want to bypass programming the FMC in).

 

Not sure if that helps, but without knowing what DT is, not much I can help you with on that.

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Climb thrust can be set automatically via the T/O 2/2 page. Or just hit N1.

 

DT = derate thrust?

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On Climb Thrust, I'd just let your Autothrottle handle this. Once you have hit your TO/GA button, everything after that should be automatic. The computer will determine how much thrust you need based on your flight profile.

 

Like Matt though, I don't know what "DT" means. You should know your weight well in advance of a couple of minutes though. Yes, if you are running your APU, some fuel will be eaten, but not that huge an amount. If you are referring to your V Speeds, those too are calculated for you by the FMC assuming you've programmed it (and this isn't an airplane that you want to bypass programming the FMC in).

 

Not sure if that helps, but without knowing what DT is, not much I can help you with on that.

DT refers to derated takeoff, to calculact the v speed with an assume temperature.

 

i know the FMC calculate all that, but for a DT (derated takeoff) i need special calculation to know how much runway will remain and the thrust precent.

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FMC will not always calculate optimal numbers anyway. Knowing your weight couple minutes beforehand is enough, its not like it takes 15 minutes to calculate the performance. Especially if you have a laptop on you, or a tablet with perf program, or you can also have your dispatcher send you the numbers via ACARS.

 

Regarding climb thrust - in itself, it means how fast the engine goes. As you know, there are limits how fast an engine can turn. Take-off thrust for couple minutes, maximum continuous... Climb thrust is less, because if you run engine at less RPM, it will last longer. So CLB is a tradeoff between performance and cost, while MCT is pure performance so you can save your &@($* if one engine quits.

 

You change to climb thrust typically at 1500ft AAL, and the NG will do it automatically. It will hold the thrust in VNAV mode or in N1 mode, if another limit is not set.

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We work out if we can derate the takeoff when we get the loadsheet, as part of the final CDU procedure. We write down our 26k N1, then use the RTOW (regulated takeoff weight) charts for the airport to work out if we can derate. Using current temperature and wind for a specific flap setting and runway, we can find our RTOW weight, and compare that to our adjusted takeoff weight (adjusting for QNH corrections, any inop items, anti-ice). If the RTOW weight (climb or runway - whichever is lower) is more than our adjusted takeoff weight, we can use that derate. So if it turns out we can use 22k, we select that, and write down the 22k N1. Conditions permitting (no contamination, crosswind 10 knots or below etc) we can work out if we also assume a temperature along with that, using our adjusted takeoff weight on the same chart. If we can do it, we enter it and enter the subsequent reduced 22k N1.

 

We then enter the flap setting for takeoff, which is when the FMC will suggest the V-speeds. But the RTOW V-speeds are the master speeds, so we work them out on the chart using our actual takeoff weight. Usually, and if you've worked everything out right, the RTOW speeds will be within a knot of the speeds suggested by the FMC, in which case you can take the FMC speeds. If they're not, we use the RTOW speeds.

 

I'm sure all this would go a hell of alot quicker if we had an EFB that did it all for us, but there's something satisfying about going up and down a chart doing it yourself ;)

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We work out if we can derate the takeoff when we get the loadsheet, as part of the final CDU procedure. We write down our 26k N1, then use the RTOW (regulated takeoff weight) charts for the airport to work out if we can derate. Using current temperature and wind for a specific flap setting and runway, we can find our RTOW weight, and compare that to our adjusted takeoff weight (adjusting for QNH corrections, any inop items, anti-ice). If the RTOW weight (climb or runway - whichever is lower) is more than our adjusted takeoff weight, we can use that derate. So if it turns out we can use 22k, we select that, and write down the 22k N1. Conditions permitting (no contamination, crosswind 10 knots or below etc) we can work out if we also assume a temperature along with that, using our adjusted takeoff weight on the same chart. If we can do it, we enter it and enter the subsequent reduced 22k N1.

 

We then enter the flap setting for takeoff, which is when the FMC will suggest the V-speeds. But the RTOW V-speeds are the master speeds, so we work them out on the chart using our actual takeoff weight. Usually, and if you've worked everything out right, the RTOW speeds will be within a knot of the speeds suggested by the FMC, in which case you can take the FMC speeds. If they're not, we use the RTOW speeds.

 

I'm sure all this would go a hell of alot quicker if we had an EFB that did it all for us, but there's something satisfying about going up and down a chart doing it yourself ;)

thanks Tom very detailed.

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