During descent, I often have trouble with descending to an altitude by a certain waypoint. It is really stressful as I am constantly changing the V/S to be on track. VNAV and LNAV for some reason never seem to achieve the correct altitude by the waypoint in the FMS. When I am being vectored I can not descend on time, and on my own with the FMS, VNAV and LNAV can not descend and maintain speed as designated in the FMS.  Any tips to make the last 15 minutes of my flight less of a stressful time and as "relaxed" as the other half of my flight?

It would be helpful if you told us what plane you’re flying so we can provide some feedback.

16 minutes ago, cmpbellsjc said:

It would be helpful if you told us what plane you’re flying so we can provide some feedback.

PMDG 737.  Probably should ask these questions in the PMDG Forum.

SPD HOLD + LVL CHG. Use spoilers to control descent rate.

2 hours ago, cmpbellsjc said:

It would be helpful if you told us what plane you’re flying so we can provide some feedback.

737

Numerous ways todo this. No way is 100% correct.  But leaving it in VNAV will provide protections and protections are our friend.  So first step is to do the math to see I'd you are truely behind.  3:1 is the descent profile that works well around 290KIAS programmed for most aircraft.  That's 3 miles to descend 1000'.  If the target altitude is below 10,000 add another 5 miles to decelerate.  If you're on target let VNAV go a bit longer.  If you're only a bit. Behind try the speed brakes alone.  If you're even further behind you can Speed Intervene and crank that speed up.  This way you don't dump all your protections in the descent.  Also, if you're really really behind you can always just dump the gear.  Oh yeah don't forget if this is a controller online that goofed up you can always say unable for constraints.  No harm no foul honestly.

Have fun, no need to stress.  Curse outloud are the virtual controller, what we do at the real ones that like to keep us high then drop us as fast as possible.

4 hours ago, charliearon said:

PMDG 737.  

How did you know? It could have been a 737, 757, 767, or 747.

2 hours ago, Billkhaled said:

737

In addition to what was mentioned above don’t forget to put in the forecast winds in the descent page. Leaving it blank can make it harder for VNAV to control the descent.

Dont be shy about using the spoilers either. The last 4 flights I was on the pilots used them every time to control the descent speed. There seems to be a “sim-ism” that they shouldn’t be used or are rarely used but that hasn’t been my experience in many real world flights.

Also if you’re using the FSX ATC I wouldn’t abide too much by their instructions as the vectors and descents will often send you way out of your way and with sometimes very unreasonable descents.

32 minutes ago, cmpbellsjc said:

How did you know? It could have been a 737, 757, 767, or 747.

Because one of his more recent question(s) was about the PMDG 737.  Go figure??

Must just learn to manage forward and vertical speed and perform some simple math.  You have a lateral distance to the target fix.  You have a vertical distance to reach at or before the fix.  You have a lateral speed to manage, and a vertical speed to manage.

Say you have a distance to the fix of 84 NM and your lateral speed is 6 NM per minute.  Simple math says you have an ETA of 14 minutes to the fix.  So take a look at your current flight level and your target altitude at or before the fix.  Subtract the target altitude from the current altitude and divide by 14.  Example, if you are at FL310 and you need to reach 10,000 ft at or before the fix, then you need a VS of at least 1,500 fpm.  (21,000 (ft) / 14 (minutes).

You then just need the proficiency in the aircraft type to manage your available controls to hit the marks you need.  Proficiency comes with practice.  Get away from only flying routes until you gain proficiency in type.  Do not shy from just taking the aircraft up and gaining experience through repetition.  ex. climb to FL310 and then practice until you can manage a descent to say 250 kts IAS with a 2.000 FPM rate of descent.  Take notes and develop a profile of what you need to do.  Most quality simulator aircraft come with operating manuals that contain information pertinent to this. Climb back up and repeat.  Repetition is learning.  

Edited August 17, 20187 yr by fppilot

Two easy general rules of thumb for descents:

For distance from the field to start your descent, take the altitude you need to lose, in thousands of feet, and multiply by 3.  So if you need to lose 25000 feet in the descent, 3 x 25 = 75nm needed for a 3:1 descent.  If you're on the approach side of the field, add 10-15 nm to be down in time to start the approach.  If you have to go to the far side of the field for the approach, you can reduce the distance for descent by 10-15 nm.  When in doubt, start a little early

For the descent rate needed to hold a 3:1 descent, multiply groundspeed by 5.  So if you're at 400 Knots groundspeed, then you need ~2000 fpm to maintain that gradient.  The rate will change as groundspeed changes in the descent (changing winds, TAS etc).

So if I'm at FL380 and a GS of 440 knots headed to a field with a final approach fix on my side of the field at 2000 ft, I need to lose 36000 ft (38000 - 2000), and so I should start down no later than 118 nm from the field (3 x 36 = 108 + 10 miles since the FAF is on my side of the field).  I'll need an initial descent rate of at least 2200 fpm (440 x 5) to hold that descent gradient. 

Of course there can be need for adjustments, but these rules are a solid starting point...you can adjust up/down as circumstances demand.

Regards

 

6 hours ago, charliearon said:

Because one of his more recent question(s) was about the PMDG 737.  Go figure??

Lol, good catch. Didn’t see the other thread.

8 hours ago, cmpbellsjc said:

Dont be shy about using the spoilers either. The last 4 flights I was on the pilots used them every time to control the descent speed. There seems to be a “sim-ism” that they shouldn’t be used or are rarely used but that hasn’t been my experience in many real world flights.

If you speak to some older airline pilots, it wasn't unknown for them to drop the gear to add a bit of drag too. That sort of thing isn't exactly in the book and would doubtless be frowned upon these days, but with the 737 being quite slippery on the descent, one can understand why it might be done, so you're in good company with pilots who know the Baby Boeing can be tricky to get down. In fact, good old Mike Ray, former United Airlines Captain and friend to jet simmers everywhere mentions having done this a few times in real life in one of his training books, although he was largely referring to the turbojet versions of the 737 in relation to that.

Edited August 17, 20187 yr by Chock

Hell, even the Flyjsim 727/737 is slippery 🙂 Kudos to Ryanair for flying the 737-200's for so long!

 

8 hours ago, w6kd said:

Of course there can be need for adjustments, but these rules are a solid starting point...you can adjust up/down as circumstances demand.

exactly ...... groundspeed/winds, arrival chart profile, atc etc.