737-800 Pitching Up

Heyo, the other day I was flying solo in the 737-700, at regional airports, seeing if I can land a 737 there. I turned on APPR as I approached, and turned on autopilot for speed. I noticed, after being perfectly aligned for APPR, so I wouldn’t dive or climb, APPR drove the aircraft vertical, and reduced engine power. Is this a glitch? It’s a good thing I stopped it on time somehow.

Hey, just to clarify where you aligned to both the runway which is shown with the middle line at bottom of the HUD, and also the Glide Slope, which is the rectangle on the right whilst using HUD.

Sometimes if you are aligned with the runway on the HUD but not the glide slope then this can happen, just wanted to clarify?

Yeah. I was on the glidescope and was aligned with the HUD.

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Oh right, not to sure then that would be? What was your speed before you engaged APPR?

Just at 182, and I set the speed to 190 1 minute before turning APPR, but never recovered, even before the insane climb.

So right when you touched the Appr button, the aircraft went flying up?

Exactly 9 seconds after turning it on. I time how long it takes from turning on APPR to touchdown, because I am currently researching the perfect speed to land in different aircraft.

I suspect your plane stalled, the A/P sometimes goes 10 knots below your set speed which causes problems mainly if there is a sudden increase in altitude or pitch let’s say which there usually is on final approach. I suggest you work out how to use the flaps to avoid stalling as easy and it might be best to set your speed a bit higher than you want in case or control it manually.

I was using flaps. And the 737 with a 17% Load shouldn’t stall.

Okay. It’s just an issue with the speed while the A/P is active. I find myself controlling my speed manually now as I get too close to stalling then I would like while using the AP set speed.

Yeah, but the speed was at 182 when it dived up, and instead of trying to recover, it actually reduced power. I also want to know why it stalled and pitched up exactly.

What flap setting?

Maximum flaps

You should not have max flaps at such high speeds. More like 140 KIAS. Even then you wouldn’t use max flaps except for short field operations where you would then use flaps 40.

Adding on to @Chatta290 comment, the average landing speed for the 737-800 is between 140 KIAS and 150 KIAS depending on weight.

Also regarding the flaps, landing at those speeds mentioned above, you would need Flaps 30, but should never need to use Flaps 40.

Also another interesting fact about the 737-800, they apparently very rarely ever use Flaps 15.