MCP SPD digits jumping too far during SPD change

[Iain]

Hey all

I have a strange bug that I was sort of aware of recently but done some testing last night on my flight of rubber ducks with a DHL 733 Cargo from Leipzig to East Midlands.

When changing speed in the MCP, let's say we are at 200 and dialing back to 190 shortly before GS intercept, I want to change to 190, I drag or scroll, digit by digit from 200 to 190, but every time I get to around 193, with 3 more clicks to go, the speed jumps to 183 on the next click,  I then need to increase it back to 190.  Happens every time, with scroll or drag.  180 to 170, jumps to 163, 160 jumps to 145 then scroll back up to 150. 

I have it on video, can post it this evening if it helps explain it.   I'm pretty sure it's not my mouse, as all other MCP functions work digit by digit.  Can't confirm if it also does this at higher speeds, but can test that later.

 

Cheers

[Litjan]

Hi Ian,

I have not seen this type of behaviour - there is a bug with the animation of the FLT ALT window when using the mouse-wheel, but not on the MCP SPD selector.

I sometimes have a "reversal" problem, where I drag to the right to increase, then drag back left to decrease a bit - but the value keeps increasing. Annyoing, but most likely an X-Plane bug (we use 100% default X-Plane manipulators).

Also make sure you can rule out "command speed limiting" - which interferes with your selection to avoid moving the speed cursor into over- or underspeed situations. Often the minimum speed is limiting and may change due to current angle of attack, flap setting,  etc.

Cheers, Jan

 

[Iain]

Ok, good points, let me check again this evening or tomorrow and will send some feedback.

[Iain]

Well, I was flying ASL Stansted to Dublin yesterday, wind shear etc, had either 3 go arounds!  Think I recorded them, so might put a video together to show off my lack of go-around skills ( I need to read up on the exact procedure), but I was able to repeat this digit jumping with the MCP, only happens on finals, it really doesn't seem to be related to the underspeed limits, but it's definitely nothing to bother about.  Will try and post a video and can also show this small "bug" and see what you think.  Any links to the correct way to do a go-around in the IXEG?

[Litjan]

We limit the speed that you can dial in on the MCP - like in the real aircraft. The lower speed is dependent on stall speed, which changes with the angle of attack. If a plane is operated in gusty conditions, this angle of attack varies - and so does the maneuvering speed.

Your normal Vref will give you 1.3 times the 1g stalling speed. So if you stall at 100kts at 1g (just level flight, no "pulling up") your approach speed will be 130kts.

If you fly in gusty conditions, you must add speed on top of this (don´t want to dig this out, but I explained the formula at least 5 times already ;-)), up to 20kts.

So in moderate windy and gusty conditions you should fly the approach at Vref+20kts. If your speed is set at that speed, it is unlikely that the minimum speed should shoot that high (and change your selected speed).

To go-around: Push the TO/GA buttons (twice for full go-around power). Raise your nose to +15deg pitch and retract your flaps to 15 degrees. Once a safe climb is established, raise the gear.

Cheers, Jan