ASN + PMDG + Descent Issues

[ALF1 15]

Correct me if I´m wrong real life Jocks, but isn´t V/S a bit old fashioned ? Mostly a thing of the past on the old autopilots. It is the pitch mode I use the least, almost always when I am doing a non precision approach and using the vertical profile in the ND.

[JoeDiamond 67]

Correct me if I´m wrong real life Jocks, but isn´t V/S a bit old fashioned ? Mostly a thing of the past on the old autopilots. It is the pitch mode I use the least, almost always when I am doing a non precision approach and using the vertical profile in the ND.

 

V/S has it's uses.  Often if I am only climbing or descending a couple thousand feet I will us V/S to keep the climb/descent smoother.  LVL CHG will try and bring the power all the way to max or idle which would be overkill in that situation.  V/S is a very basic mode but I certainly wouldn't call it old fashioned.

[downscc 1,327]

 

 

V/S is a very basic mode but I certainly wouldn't call it old fashioned.

 

Agree, it definitely has its uses. For example on a downwind I'm at 8000 cleared to 4000 ahead at the turn to base, perfect time to dial in a leasurely 500-800 fpm descent to keep the ride smooth for the pax. It's also a handy alternative for those times the pitch modes goes into VNAV SPD, using V/S and managing the speed myself instead of letting the automatics do it.  Finally, there is the step climb that I almost always will use V/S to transition to the next level but this is the only time I ever use V/S in a climb and then I have an eagle eye on N1 to ensure I stay on the side of excess power available and away from no excess power available where speed decays.  To me using V/S in a climb at thrust limits is just crazy, I wouldn't fly with that pilot again.

[JoeDiamond 67]

Just my technique but I would never use V/S for a step climb as you have no speed protection. You would be much better off using VNAV in that situation. I would not recommend using V/S for any climb up at high altitude.

 

I don't use V/S much to climb, mostly for descents. If I'm climbing in V/S I'm down low and I'm not climbing more than 1000-2000 feet.

[BlueStar 323]

VNAV makes it easy.  It seems like just yesterday we were going to Flight Idle at TOD and descending at .80/300.  The TOD was calculated by the FE using an E6B.  Fuel planning was 3,000/engine/hour and was always seemed to make a good estimate.   

[pcubine 143]

but isn´t V/S a bit old fashioned

Old fashioned or not, if it works for me I will use it.

I would never disconnect the A/T to be able to descend at idle

I think you misread my post. I don't disconnect the A/T to descend at idle. At certain points during the descent, I disconnect A/T to prevent the FMC SPD from becoming active.

[kevinh 409]

I have done that in the past but I really don't want to begin accelerating with 240 kts. several mile away. Giving it thrust to prevent FMC Speed from kicking in is that same as FMC Speed kicking in.

That's what I started with four years ago and I guess old habits just die hard.

FMC speed is only coming in because speed is getting too low on the VNAV profile. So adding thrust isn't accelerating you as such it's keeping speed where it should be. I don't try and fight against it.

[Driver170 42]

If i'm low on profile, i reduce the ROD by using V/S until the correct profile has being re-established. Then re-engage VNAV and continue monitoring the profile.

 

If i'm vectored off the STAR, the use of LVL CHG makes the CDA descent path control quite difficult since allowance must be made for distance covered during any speed changes and it takes experience or careful thought to be able to estimate this accurately. Use of V/S and the green altitude range arc makes flight path control very easy while speed control can be easily achieved by use of speedbrake and flaps if needed. But LVL CHG is the better choice for me at times when max descent rate is required.

 

For the final approach i certainly use V/S so in order to finesse G/S capture.

 

Thats my take on V/S much of the time.

[pcubine 143]

So adding thrust isn't accelerating you as such it's keeping speed where it should be

I realize it is not accelerating but only trying to maintain the target speed as shown on the PFD. I question why it begins to accelerate to 250 knots when in 3-4 miles the target speed is going to drop to 240 knots and the NGX is already at 243 knots. I guess I just don't agree with profile for this STAR and Approach. FOOXX FOUR, ILS 19R at KTPA.

[kevinh 409]

Surely the best option is speed intervention in that case.

[pcubine 143]

Surely the best option is speed intervention in that case.

I will try that next time. Thanks.

[Budbud 227]

The only time I use V/S in climb (in the sim) is if I have a altitude restriction at or below for which the climb in VNAV SPD would lead to a level off shortly before the waypoint.

In that case, I would go for V/S to reduce a bit the climb rate in order to go smoothly through the alt restriction to prevent the aircraft to level off, reduce engine thrusts then spool again to thrust ref to continue the climb.

It seems to me a bit more bumpless and smoother.

 

Otherwise, I use the V/S mode quite often on approach when there is a portion of radar vectoring to transition from the STAR to the final approach, to avoid getting too low too fast.

For some approaches, the STAR will bring you to FL100 30-40nm away from the IF, and then you would have radar vectoring to join the IF at for example 3000ft. In this case, I would like to avoid flying 10-20nm at 3000ft.

[ALF1 15]

Oh I definitely wont do this Budbud, giving up the autoflight capability at a critical time not for me.

 

Try the FLYZA3 departure on runway 15L out of KIAH. I am definitely engaging VNAV and let it do the work.

[Budbud 227]

 

 

Try the FLYZA3 departure on runway 15L out of KIAH. I am definitely engaging VNAV and let it do the work.

 

I see what you mean and I should have been clearer in my previous post.

 

I never use V/S for initial climb either or below the MSA. I use it only for higher climb usually above fl100 for altitude restriction like to cross at or below fl160 for instance on some departures and it depends of course on the geographical situation, high terrain aroung...

 

In the FLYZ 3A, I agree with you that using V/S for both the first altitude restriction of below 4000ft and 5000ft is definitely a no-go to me as well.

[ALF1 15]