Has anyone attempted a manual descent using a different mode than VNAV?

[Anxu00 176]

This plane hand-flies very well but I always seems to be in over speed when using V/S and select a descend.  I have read in the system doc that the throttles need to be managed but there is no example.  Aside from V/S mode which other mode can I use for a manual descend?

 

Thanks in advance.

[dmbusmc 46]

Hi Vu,

 

I've done quite a few. The basic modes are VNAV, V/S, and PITCH HOLD. You can even use all 3 interchangeably. To give a good example, last night I flew KPUW-KSEA, and was expecting 16L, and Set up VNAV accordingly. Then, low and behold....runway change and got assigned 34R. That put me in a pinch since it gave me a lot less time and distance to descend. So, I switched to V/S, set it at -2200, managed my speed by reducing the power a little more, got the chart out, etc.

 

As for managing your speed and throttle, it's all on you and the situation. There is no real set way to do it other than the very basics- need to slow down? Reduce the power. Need to speed up? Increase the power. The best way to do it is go by 5's on your torque, set the power, and leave it for a few seconds and see what it does.

 

For an example, your at FL200 and 265kts, and are going to descend at -1800 fpm.

 

- Once you begin your descent, pick an airspeed you want to hold and bug it, say 260 kts to 10000 ft.

 

- Next, pick a power setting on the torque. At 850 RPM, pick for example 25%. Once you begin your descent set your power to 25% and leave it there, and see what it does.

 

- If you find your speed is still increasing, decrease your power to 20% torque. Leave it, and see what it does.

 

- On the other hand, if you find your speed is decreasing below 260 with 25% torque, increase it to 30%, and see what it does.

 

- Once your airspeed is stabilized, then you can fine-tune it more to be more exact.

 

Keep in mind that performance changes with lower altitudes, and you will have to adjust as necessary. This applies for any mode of descent. Keep in mind though if you use PITCH HOLD that both your v/s and airspeed will change with power settings, so that will be the most difficult to manage.

 

Hope this helps!

[Andydigital 93]

I've not tried it myself yet but I am pretty sure you can use IAS mode too, that will adjust pitch to keep a set speed, if you pull the PL's back to almost idle you should get a good rate of descent with a speed set at 220 to 240 or so. Guess what I am going to try now in FSX, lol.

[dmbusmc 46]

I've not tried it myself yet but I am pretty sure you can use IAS mode too, that will adjust pitch to keep a set speed, if you pull the PL's back to almost idle you should get a good rate of descent with a speed set at 220 to 240 or so. Guess what I am going to try now in FSX, lol.

 

You can, I totally forgot about that ^_^ .

 

For that, power will change your V/S, more power= decreased -V/S, less power= increased -V/S, and airspeed remains constant.

[martin-w 3,234]

Anxu00, on 29 Apr 2013 - 6:00 PM, said:

 

This plane hand-flies very well but I always seems to be in over speed when using V/S and select a descend. I have read in the system doc that the throttles need to be managed but there is no example. Aside from V/S mode which other mode can I use for a manual descend?

 

Thanks in advance.

In regard to the title of this topic...

 

Of course! It's basic piloting. Very simple in vertical speed mode. Generally speaking you will find up to -1800 feet per minute is fine. Simply throttle back accordingly, so as not too overspeed. No different to any other aircraft.

 

IAS mode is also permissible but personally I haven't tried it yet.

[Anxu00 176]

Thanks all for sharing your experiences.  There were not much aircraft data about Vne etc. only two tables with take off and landing performance with various flaps setting.  It's a certainly a fun plane to fly.  

[747-fan 19]

I usually fly on Vatsim, and live ATC tends to clear you down to STAR waypoint appropriate altitudes in good time. I've rarely had to ask for descent.

I usually descend on IAS mode, having low RPM set and throttle at near idle I tend to end between 1800-2200fpm. It changes the lower you go. That's why I prefer IAS, it guarantees you keep a decent speed with the engines at idle and adjusts VS to suit. It also guards you from overspeed and stall speed. Just remember that VNE lowers the lower you go.

I have no idea if this is a correct procedure but it keeps things simple to me and I've never had any VATSIM or IVAO complaints.

[Q_flyer 766]

I believe most Q400 SOP's use IAS in the climb (eg... 185 after flap retraction, and 210 after 10,000'), but VS in the descent.

 

As far as I can see, a lot (possibly most) Q400s don't have VNAV, and have 'INOP' where the VNAV button would be. (This is the case with most of the FlyBE fleet).

 

So we're lucky to have it fitted to our Majestics :wink:

 

Oh and ............ Remember your ALT SEL :smile:

[ajaybala 66]

i just bought the plane yesterday. i did not read anything but using common sense looked for the apu, started it and then went on to start the engines using the starter switches. did not compute init ref or even turn on the fms. just set flaps 5, added power and rotated at 110 knots. to me it seems that the controls are not as responsive as the aircraft seems to follow the motion of the yoke with a delay of maybe half a sec or more. this behaviour forced me to think ahead and i turned for final into khqm and landed at about 100 knots with the throttles halfway. so this bird does require some serious power applied while landing. landing was a breeze, un- managed, with the flaps fully applied. sorry about the lack of pictures as i have yet to master the fine art of taking screenshots. happy flying.

[Nathan3219 113]

I never use VNAV. Never.

 

Here's what you do. Cruise altitude - altitude you are going down to * 3.

Example: At CI06 you have to be at 2000. So, if you are crusing at FL260 then you do (26-2)*3=72. So 72 miles out.

 

Now to find out your FPM down. GS in kt / 2 * 10 = xxxx vertical speed.

Example: Cruising at 320 kts ground speed. So, 320/2=160, and 160*10 is 1600. So you would go down 1600 feet per minute during your descent.

 

 

I hope you might find these equations useful

[Fabo 213]

I am also used to not using VNAV. I flew the Tu-154 a lot before I switched to FSX and got used to computing my own TOD. I will just need a couple flights in the Dash to find the sweet spot... I used to be able to routinely do power off descends from cruise down to 1000ft AAL just by eyeballing the proper TOD and playing with speed a bit. I expect to get to a similar point with the Dash.

[Skysurfer7 34]

3° flight path:

FL / 3 = dist. to start decent

ex:cursing at FL240, 240/3=80, start decent 80 nm out

 

To check during decent, if on a 3° flight path:

Dist x 3 = FL you should be at

ex: I'm 50nm from runway, 50x3=150...I should be at FL150

 

Sinkrate = half the GS x 10,

ex: my GS is 240kts, 240/2x10=1200 f/m, or 24/2=12 & just add two 00's =1200 f/m

[Morph 9]

Not quite correct.... :Nerd: For 3° descent path:

 

FL / 3 = dist. to start decent

ex:cursing at FL240, 240/3=80, start decent 80 nm out

 

To check during decent, if on a 3° flight path:

Dist x 3 = FL you should be at

ex: I'm 50nm from runway, 50x3=150...I should be at FL150

 

Sinkrate = half the GS x 10,  ex: my GS is 240kts, 240/2x10=1200 f/m,

or 24/2=12 & just add two 00's =1200 f/m

 

 

 

You basically just re-quoted what he said? lol 

[Skysurfer7 34]

You basically just re-quoted what he said? lol 

Really? there's a difference between FL/3 = dist. to start decent & FLx3 /10.......LOL!

[sandpatch 9]

Many aviation thumbrules here: http://www.peter2000.co.uk/aviation/misc/B737mrg_thumbrules.pdf