B737 losing speed on climb

There have been some topics on this issue but they have been with heavies so Im not sure if I will get the same response with a 737. I was flying from KPBI-KATL on a 737-800. I was climbing to FL380, around FL320 I noticed by speed was at 116kts. My vs was set 3800 I think. I set positive trim at calibrated my device then disengaged AP to recover from the stall I was about to enter. I pulled all the way back almost falling backwards in my chair and the nose was still pointing down. I eventually recovered and set my vs to 1000 clicked vnav and set auto throttle. After that the speed was just stuck at 167kts. It just wouldn’t gain any speed. In some previous topics people said to step climb but that seems like that is ment for heavies. This has happened to me about 4 times already. It’s only happening with the 737. What am I doing wrong?

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Your VS was 3800 all the way through? 😳

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3800 fpm is way too much for a 737. Also, your airspeed decreases at higher altitudes.

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There’s lots of factors that could be in play here. The main one is once you’re above FL280, climbing at 3800 ft/min will make you stall just about every time. You should climb no faster than 1500ft/min past FL280.

You also will probably not be able to maintain airspeed at FL380 unless your aircraft is very light. Knowing your load would help here.

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How heavy were you.

BTW your V/S should only be at 2800 at the most, I do that all the time and its fine

Step climbing is not only for heavies, it’s for any aircraft that’s too heavy for their altitude. Looking at the details you described, you were probably too heavy for your altitude. Also like others have mentioned, 3800 V/S is way too high for a planes nose/pitch to be. If you remember, what was your speed while climbing, both under fl280 and above fl280?

3800 too high

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Use Simbrief or fpltoif.com (with the Simbrief feature) and you’ll have a good idea of what altitudes you need to be at and the appropriate V/S. Or if you wish to you can dig up the 737 FCOM (flight crew operations menu) to get good numbers but that would probably be a lot work.

Stall recovery needs the opposite action, push forward to gain air speed rapidly. Pulling back only worsens things.

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The reason why you stall is because you are very low in speed and your plane can no long climb. So why continue trying to hard to lift the nose up? The plane is trying to gain speed and recover so just let it gain speed and recover.

Also you may want to turn on the seatbelt sign so the passengers don’t fly to the ceiling.

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I imagine the seatbelt sign would be down the priority list a bit in that scenario!! 🥺

So the basic stall recovery actions are push forwards (nose goes down and air speed increases) then full power (this minimises the altitude loss which could be critical near the ground).

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The real issue here is about using vertical speed as the primary flight control input… That’s not a good idea.

The vertical speed should really follow as a cosequence of the main control inputs, which for climb are pitch and power. Setting these appropriately will allow a good VS to follow naturally.

Too heavy for that steep of a climb. If it were a shorter flight with less fuel, it would be grand. But that’s quite a steep climb for that long of a flight.

Vertical speed at 3800?!! That’s too high! I think it’s the main reason for the stall and at FL280 your speed decreases so you have to reduce your VS to about 2500 or less.

And in case of stall Push forward, regain speed and gradually pull up.

Sounds like everyone above has covered everything… v/s should never be set to 3800 unless you are following an odp (obstacle departure procedure) which requires that climb gradient, and you have the aircraft performance/ weight and balance in order to achieve that. The only thing i would add is if you get into a stall situation add some more power as you push the nose forward. In the cessna we always add full power to recover, however I dont know the procedures they do irl in the 737-8.

My standard t/o climb strategy on almost any aircraft is this (this is quite realistic too):

Step 1: Increase your throttle to around 80% for long runways, 85% for medium and around 90% for short. This is quite realistic and is used in case an aborted take off is needed, less throttle = more time to react.

Step 2: Rotate off the runway and slowly lift the nose to about 15 degrees. You can use the HUD the help you (15 degrees is the third green line on the HUD)

Step 3: From 1,000ft to 2,000ft (on an airliner) slowly begin to raise the flaps. Do this slowly because obviously the flaps will create less drag as they retract and cause the plane to speed up considerably. At this point, also begin to lower the nose to 10 degrees and allow the plane to speed itself up to around 230 knots.

Step 4: Make sure your plane is on route and allow the plane to speed up at lower altitudes to allow for room to slow down higher up. I usually do ~247 knots below FL100 then increase to around 270 knots above FL100.

Tips:

  • Consider the wind, if it’s blowing hard directly at you, you might need to turn to speed up the aircraft.
  • Ensure your plane is light enough to do what your telling it to do. Many long haul flights need to climb slowly or step climb to reach their desired altitude and almost always considerably increase their altitude a third or halfway through a flight after burning a large amount of fuel and making the aircraft lighter.
  • It’s normal for an aircraft to be going 220-240 knots airspeed at FL380 because the ground speed is usually much higher, closer to 400 or 500 knots.
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Sounds like you’re trying to use the VS as IAS hold. Everyone is right that as altitude increases, indicated speed & climb rate decreases. This is due to less air moving over the wings at higher altitudes.
In the sim you can manage your VS by adjusting it in relation to your indicated speed, but this must be done throughout the climb. Many of us in the community have talked about our desire for IAS hold which would change the VS automatically whilst holding a selected airspeed or mach. I hope this helps clear up somethings. Keep the blue side up!

Hey, the problem here seems to be that you are too high on the V/S, doing 3800FPM at FL320 is not a viable option. Almost no airliners takeoff at 3800FPM, which lets you know that climbing at 3800FPM at FL320 isn’t good for your engines nor your speed😂. I can give you a recommendation on what climbing methods you can use for the 738.

I normally do

1300 initial climb V/S
2800-3000 climb to 10,000
2400-2600 climb to FL200
2000-2200 climb to FL280
1000-1700 climb to cruising altitude

Also, regarding my speeds, I do

250 to 10,000
292 from 10,000 to FL280
and M.78 from 10,000 to cruising altitude

Hope this helps in your upcoming flights.

From experience, I know the 737 climbs between 3000-3500fpm. However, the aircraft pitch decreases the faster you go. FPM does not necessarily mean your pitch will be the same pitch you had at 2500ft - it means how much alt you are gaining per minute despite your pitch (Ex: you could be at FL280 and have a low pitch but still having the same FPM when you were at FL150 with lower speeds). The two possibilities are: 1) You did not increase your speed resulting in a high pitch leading to a stall at high alt 2) Your aircraft load was too much for the altitude you were trying to maintain. In general, a stall at a very high alt is hard to recover from, resulting in an irreversible nosedive. I know for a fact there is nothing wrong with the 737 because I have been in your positions before, and I have learned from my mistakes.


If you have any more questions feel free to PM me. Have a nice day and safe flying! :)

Best,

American

(For the experience I mentioned on my flight from EWR - TPA United 737-900 I asked the pilot flight parameters he mentioned 3700FPM and decrease to 3400 once at or above FL100)