solved A/T during final and FMC calculated landing speed

[Kristo1]

Hey,

I have a few questions I haven't really bothered to check up on for quite a while. But I did a few flights today and thought I might inquire a bit. My first question is about the auto throttle. When I'm on final the letter B usually appears next to the speed readout for my auto throttle, disallowing me to set the speed any lower than than around 190 kt. It usually goes away again right before touchdown, but this will often cause me to come in too fast Do you have any idea why this restriction is there and what I can do about it? I know that the throttle is usually controlled manually during final, but that doesn't work too well for me since I don't have a throttle lever on my joystick to control speed, so I prefer to use the auto throttle until right before I hit the ground. 

Second question is related, and is about the calculated FMC speed. If I set the configuration for flaps full in the FMC it will usually give me a landing speed way lower than what I'm used to with the airbus. Maybe around 115 kt. If I actually try to fly in with such low speeds the airplane usually crashes in front of the runway. So I will often aim at a landing speed at around 135 kt, which seems to work better, in spite of being to opposite of what I'm being instructed to do. But what am I doing wrong here? 

A final question is unrelated, but I prefer to fly at dusk/dawn or night and the lighting in the cockpit isn't terribly believable under these circumstances. For instance if I'm flying away from a setting sun, it seems to light up my cockpit through the back wall, leaving it way too bright, until the sun disappears behind the horizon, when it goes completely dark, almost in an instance. Is there any plan for fixing this, or a custom fix? And if not, is there any payware out there with great cockpit lighting effect for dusk/dawn/night flying?

Thank you so much in advance if anyone responds!

      

Edited March 1, 2018 by Morten

[mmerelles]

About your first issue. This is the A/T system protecting the aircraft during a dirt configuration (takeoff and approach)

-If you want to increase the speed, you need to retract the flaps as per the flap schedule, otherwise A/T will not allow speeding the aircraft beyond current flap setting capability not to rip the surfaces.

-If you want to decrease speed, you need to extend the flaps as per the schedule, otherwise A/T will not allow the aircraft to reduce speed below the minimal current flap maneuverability speed no to stall and crash.

note: make sure you do not use any hardware lever as an axis, unless you use a detent plugin or similar. Otherwise your potentiometers nois/spike will keep moving the flap position no matter you are not touching at them

 

About your second issue. Calculated VREF speed for landing is based on aircraft GW (Gross Weight) for the given flap options. If you are getting such a crazy low speed values, this would indicate you did not load anything on the aircraft during pre-flight.

Before departure:

1. Go to GROUD SERVICES menu

2. Select REFUEL TO xx tons of fuel as required for your trip

3. Adjust ZFW to around 50 tons or similar (this is pax + cargo)

4. press Instant to load everything.

 

This will result on an average packed aircraft and you will see what IXEG flight model is all about, you will actually feel the weight during TO pull and landing.

 

note: for the purpose of landing on calm days, you have to configure VREF +5 knots on the MCP SPEED DIAL during approach to cross the runway threshold at that speed and you bleed off those 5 knots during flare while you retard the throttles to a VREF touchdown.

Landing on windy conditions require more complex calculations to the VREF +XX, you can experiment later on this once you materized the above.

 

hope this heps

Edited February 27, 2018 by mmerelles

[fffirefly]

Well I won't comment on your first two questions as a great job has already been done.

As for the third, this must be an x-plane thing as I have experienced the same in various aircraft.   Sometimes the sun is reflected on the panel but when you go to an external view the sun is below the horizon.  Don't have a fix but I'm sure they are aware of it.

[Litjan]

Hi Kristo1,

1.) You are experiencing the speed reversion mode of the autothrottle. The flashing 8 is showing that the autothrottle is stepping in to save your aircraft (either limiting your speed to prevent overspeed or adding thrust to save you from stalling).

You should never see this in normal operation. Read up on the "flap-speed schedule" and adhere to it. Technically there is nothing preventing you from using the autothrottle to control your thrust all the way to touchdown, even in manual flight. Just be aware that it will automatically retard your thrust levers when you pass 27ft radar altitude.

2.) If the FMS calculates "wrong" landing speed it is usually due to the user putting in wrong data. Make sure that your GROSS weight is correct. A common error is to put in the Zero Fuel Weight in the Gross weight field - then the FMC´s computed weight will be "too light" by the amount of fuel it senses in the tanks. You can always doublecheck your FMC speed computation by looking at the placard over the window. Add at least 5kts to this "Vref" to get the "Vtgt" (target speed).

3.) This is actually and X-Plane bug. They are aware of it, but it seems to be (like many other lighting-related bugs) not easy to fix.

Cheers, Jan

 

[Kristo1]

I did a test flight now and it seems the low vref speeds were indeed due to the fact that I have been loading my aircraft too light all this time! I also tried adhering more strictly to the flap-speed schedule, and it made for a much more stable approach. So, thank you so much to all of you for your thorough answers and lets hope x-plane fixes the cockpit lighting bug at some point

Cheers!