Question regarding the B737 family

So I noticed that flights operated with the B737 family often tend to cruise at very high altitudes such as FL380 to FL410. However, when I try to do this in IF I can’t pass FL350 without my throttle going super high. I haven’t had this issue with the A320 family or any other plane. I know I’m not too heavy since I take the amount of passengers that the plane has IRL and I take around 3 tons of cargo.
What am I doing wrong?

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Depends on your rate of climb. If you are climbing at a high rate - then you won’t make it high up.

Above FL300 you should be climbing at +1000fpm max

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The b737 is designed so that you climb and cruise at 70-80% throttle but it doesn’t do a lot of wear I don’t think

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When I pass FL350 my throttle is at around 85%. If I try to go higher than that my throttle will only go higher. It’s literally impossible to climb to FL410 but they do it IRL…

85% is pretty normal tbf. It’s Acc better for the engines to be at a higher N1 according to something I heard.

It will then neutralize at cruise and your pax will hear nothing while you’re climbing

Is it normal that my throttle goes over 90% at some point when I only use 86% for takeoff? I don’t think so

I am flying right now Boston To San Francisco I am at FL400 and my throttle is 83% N1 89%

How high was your throttle while you were climbing?

I wasn’t paying much attention when I was climbing but it was smooth I think I was doing 1200 fpm from FL360-FL400

another thing you have to look at is winds cause a strong head wind will make the auto throttle climb to match your preferred speed

So far I still haven’t gotten an answer to my question. I wish to know why my throttle goes very high when I try to climb to realistic altitudes. When I means high I mean around 90% throttle, not N1.

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It’s different for every situation but the speed you set for that altitude will also change it

May I ask what route you are flying @Philippe_Gilbert

The route doesn’t really matter since it happens pretty much every time I fly the B737 family.

How heavy were you?

Well from what I’m seeing almost every 737 flight I fly, the IRL aircraft doesn’t go above FL370. Sooooo I was just wondering what route

Hey, most B737s right now, due to the current state of aviation and with the pandemic, are running quite empty, hence they can climb straight up to FL390-410. Try lowering passenger and cargo loads to get realistic weight factors. I’ve tried that and it 100% works.

The reason your throttle is going up so high is because the aircraft is to heavy. As a heavy aircraft begins its climb up to high altitudes, the air gets less dense and much colder, and so the engines have to work much harder as well to try and compensate for the same levels of thrust to keep the plane flying.



It’s not just because of the pandemic, even before they would cruise at very high altitudes.

Well that’s not necessarily the case.

I tend to cruise at FL360+ in the 737 series, mainly because I fly Southwest, and they tend to cruise up high in the 370-410 range as you mentioned. I don’t have any problems climbing that high, even on 4-5 hour flights.

Your throttle is gonna go up, I mean it needs power to get there. I usually climb at 1000fpm from FL300 upwards. Weight and trim might also be a factor. I recommend a trim of +10-15 for climb in the 737. 86% is pretty low power for a takeoff, installs do about 90-93 percent throttle. Don’t be afraid to use your engines, you have two for a reason 🙂

I use similar passenger and cargo loads to what you said in your original post, so something isn’t adding up here.