hello all

i have a problem with my ngx at T/D , which is when i arrive to T/D point and aircraft start to descent , the descent is not stable , what i mean the Vertical speed is go from VS-1500 to VS-1800 and again from VS-1800 to VS-1500 and again again ( the value of VS is only example , it's also make that with VS-2000 and higher ) .... ,  which make the descent is unstable , i found my friend also have the same problem but the only diffrance i buy the aerosoft cd and he buy it from the internet

------

additional information :

this problem is with 95% of routes , the aircraft is full updated , the routes from route finder , i try the weather completely clean and zero wind speed and the problem still existing , airac 1308

i hope you can help me

Thanks

 

This is strange. I only get this when FSX decides to unrealistically change the wind direction/speed during the descent. Do you have any turbulence affecting the airplane?

This is strange. I only get this when FSX decides to unrealistically change the wind direction/speed during the descent. Do you have any turbulence affecting the airplane?

 

i try it with zero wind speed and full clear skys and the problem still existing :(

Does it happen at a specific altitude? It is natural for the climb/descned rates to vary as you pass through different altitudes. Also, it is natural for the V/S to decrease in magnitude when you need to either slow down or speed up. Maybe this is your problem? This would be easier to diagnose if you had a short video illustrating the phenomenon. That way we could see if what you're seeing is normal or maybe some sort of bad install.

The autopilot of the NG will generally oscillate, especially if you have a fast descent. A plane pitching 2 degrees up and down during descent might be uncomfortable for the people in the back, so what i do is reduce the speed for the descend. For example, my cruise speed is .785, so i'll set the descend speed on the CDU to usually 270/.76 or if i want a slower descent 260/.75

I'd also look at your flightplan and the related altitude constraints: these don't always result in an even rate of descent.

 

I notice at times that as I pass a waypoint, I jump from perhaps being below the planned descent to above or vice versa.  You may be best to control vertical speed directly and set it to 1,600 or 1,700 FPS and see where you end up on approach. 

Start a descent now (Altitude Invtervention or Decend Now) about 3-5 miles prior to TOD which will start a shallow -1000 fpm descent.  It will catch the path within a couple miles and smoothly capture the profile.

 

Make sure you retard your Physical Throttles and also press F1 on the keyboard to verify throttles are fully retarded.

 

See if that smooths out at the TOD.

@Kjjj11223344 : no not at a specific altitude , it always make that when i start to descent at any altitude , but i notice that when i am cruise very high ( like FL380 or FL390 ) the VS become more aggressive like VS-2400 to VS-2800

The speed of descent i let it control by the FMC ( VNAV & LNAV ) and i remember it's always be something between 300 to 313 IAS

----------------------

@mrtk311 : i let the VNAV and LNAV control everything , the speed of my descent is control by VNAV and value is always something between 300 to 313 IAS , ( i see it in the Decs Page in the FMC )

----------------------

@ailchim : i let the FMC by VNAV and LNAV control everything until i capture the localizer on the approach , The VS and IAS control with VNAV , i don,t make anything , because i fly a very high Technology aircraft and i put a route so i let my VNAV & LNAV control everything of my flight

----------------------

@sgreen91 : the throttles always be on idle while descent, but with control of VNAV not me

 

 

 

@Kjjj11223344 : no not at a specific altitude , it always make that when i start to descent at any altitude , but i notice that when i am cruise very high ( like FL380 or FL390 ) the VS become more aggressive like VS-2400 to VS-2800

The speed of descent i let it control by the FMC ( VNAV & LNAV ) and i remember it's always be something between 300 to 313 IAS

----------------------

@mrtk311 : i let the VNAV and LNAV control everything , the speed of my descent is control by VNAV and value is always something between 300 to 313 IAS , ( i see it in the Decs Page in the FMC )

----------------------

@ailchim : i let the FMC by VNAV and LNAV control everything until i capture the localizer on the approach , The VS and IAS control with VNAV , i don,t make anything , because i fly a very high Technology aircraft and i put a route so i let my VNAV & LNAV control everything of my flight

----------------------

@sgreen91 : the throttles always be on idle while descent, but with control of VNAV not me

You can program the VNAV through the CDU, instead of the MCP to follow a slower speed, this will make your T/D earlier though. And a much more smooth descent.

The lowered speed should help, but it still shouldn't oscillate like this even with high speeds.I use cost index 500 on many flights, and my descent is smooth. And this is with real weather, FSX turbulence affecting the aircraft, etc. Of course, sometimes FSX randomly creates a 180 degree windshear which throws the plane off a little, but other than that and the occasional turbulence, my descents/climbs are smooth. Unless, maybe what I consider smooth you consider oscillation  ?  I have noticed that once you're passing through FL300 or so, that when you're climbing, the climb speed seems to increase for a while if under level change or VNAV speed (this is consistent on every flight, and I assume it has to do with the speed of sound changing significantly around this altitude which in turn makes the aircraft pitch up to maintain the current mach number). Thus, I expect that on the descent, the V/S also changes as the plane tries to maintain a given mach. Other than that, the V/S should remain fairly constant in any of the pitch for speed modes, unless the plane is trying to level off for an altitude constraint or if you have started the descent too late (in which case VNAV tries to manage your energy by changing the commanded speed, which results in varying, and sometimes rather high, rates of descent).

The lowered speed should help, but it still shouldn't oscillate like this even with high speeds.I use cost index 500 on many flights, and my descent is smooth. And this is with real weather, FSX turbulence affecting the aircraft, etc. Of course, sometimes FSX randomly creates a 180 degree windshear which throws the plane off a little, but other than that and the occasional turbulence, my descents/climbs are smooth. Unless, maybe what I consider smooth you consider oscillation  ?  I have noticed that once you're passing through FL300 or so, that when you're climbing, the climb speed seems to increase for a while if under level change or VNAV speed (this is consistent on every flight, and I assume it has to do with the speed of sound changing significantly around this altitude which in turn makes the aircraft pitch up to maintain the current mach number). Thus, I expect that on the descent, the V/S also changes as the plane tries to maintain a given mach. Other than that, the V/S should remain fairly constant in any of the pitch for speed modes, unless the plane is trying to level off for an altitude constraint or if you have started the descent too late (in which case VNAV tries to manage your energy by changing the commanded speed, which results in varying, and sometimes rather high, rates of descent).

 

i always start descent at the T/D point , what the normal speed you are using when you descent !? ( what i mean what is the safe/normal/average speed you put it in Decs page in fmc before you start your descent )  , because i always use the value that the fmc given to me without change it !? ,  and if i try to change it what should i change IAS or Mach !?

i always start descent at the T/D point , what the normal speed you are using when you descent !? ( what i mean what is the safe/normal/average speed you put it in Decs page in fmc before you start your descent )  , because i always use the value that the fmc given to me without change it !? ,  and if i try to change it what should i change IAS or Mach !?

I always start exactly at T/D also, unless Vatsim ATC tell me to begin my descent earlier than the FMC tells me. But 90% of the time I start at the T/D point also. As for speed, I always use whatever the FMC commands also (again, unless the current situation demands otherwise, such as if I am being radar-vectored, or if I'm above or below VNAV path and need to get back on it). As for an actual IAS or MACH number, that depends on the cost index that you use. But like I said before, I use cost index 500, so my descent/cruise speeds are always very very close to the over speed red line. As for using IAS or Mach, if I remember correctly, I think the plane automatically switches over between the two when passing a certain altitude. However, you are free to use either one really, but I think it is better to use IAS when you're cruising and just beginning the descent and IAS when you're at lower altitudes, obviously. But like I said, I think it's mostly your preference (don't quote me on this how as I am not a real pilot, however you won't necessarily be doing something bad to the plane by using IAS vs Mach.) Whatever speed you maintain, however, it shouldn't be oscillating excessively as you describe, and if it remains stable, as it should, your V/S should remain relatively stable also.