3 to 1

[Gorilla]

At least in the 738, VNAV bites in terms of passenger comfort. The nose is all over the place, 1000 fpm to 3500 fpm and back. IMO the best bet with many VNAV transports is to use the VNAV path cues as guidance, but to maintain the path with V/S.

Anothe bad VNAV scenario. VNAV descent is programmed for .78/300. The computer generates a path. You start down. ATC calls "Slow to 260 for sequence." You plug in /260, EXECUTE, then watch as the airplane buries the nose to try to get to the recomputed path. DRAG REQUIRED, etc. The descent is botched. I like VNAV for everything except descent from cruise to vectoring altitude.

 

[PapaK]

I agree with 3/1 plus 10. It has worked in every jet that I have flown. The VNAV in most jets is usually defaulted to 3.0 degrees It;s usually amendable if you dig down a few layers in the software. It works particularly well if you insert the predicted winds in the descent. Some of these units can't deal well if the headwind/tailwind is over 50 kts so in that event, we often adjust the bottom-of-descent point altitude constraint by adding or subtracting mileage.

Airbus demonstrated a minimum fuel concept package on an A-300 back in the late '80's. All components of aircraft configuration were controlled by computer in order to achieve absolute minimum burn in the descent, approach and landing. The computer adjusted bleed valves, pressurization, lowered the flaps as needed and eventually lowered the gear (in a timely enough manner that the "three green" illuminated at about 100'!). All this to save 300-400 lbs of fuel. Newer aircraft with FADEC controlled engines and VNAV save nearly as much without the anxiety and loss of operational control. Ain't progress wonderful?

I use VNAV almost all the time, but I always have the 3/1 plus 10 calculated as a benchmark. The art of the deal is in utilizing the appropriate degree of automation for the situation.

 

[sleddriver71]

In the King Airs I typically use a 3 to 1 descent from cruise unless terrain dictates something steeper. When I fly the PC-12, I use a 6 degree descent. It works just fine, pull the power back to idle, flight idle and set in the appropriate descent rate depending on ground speed. I like to stay high as long as possible, especially in a single. I would fly steeper descents in the King Air but the pressurization can't keep up in ours and it just becomes an unpressurized airplane when you pull the power back to hi idle. You would think with two engines supplying bleed air it could do at least as good of a job of pressurizing. It may have everything to do with the aircraft all being about 30 years old. I've never flown a King Air 90 with low time, maybe they work as good as the PC-12 in this regards.

 

[Guillotine007]

1:1 descents are the most fun on approaches. dealing with pax and atc, 3:1 is probably the way to go though