Rate of descent?

[Alan_A]

I think I know the answer to this question (it's "no" ) but I'll ask it anyway - is there a rate of descent that keeps babies and default ATC equally happy? In the Strat I generally aim for 300 fpm on the way down, and mostly do without ATC. Today, on one of my first extended Connie flights, I decided to take advantage of its more nimble performance and brought it down from cruise at 1000 fpm. ATC was thrilled. Babies weren't.

Judging from the C-69 Flight Operating Instructions, 4-600 fpm seems to be the desired target. Wondering if any of you are being more aggressive or less aggressive?

While there are things I like about default ATC (quality of voices, ease of use) I could be persuaded to do without it, and shift over to PF3 or ProATC-X, or just handle my own flights and contact tower for approach. So if that's the solution, I'm good with it.

But let me know if there's something I'm missing.

As always, thanks in advance.

[blillpers]

I've found the 500fpm range to be about right. That way you can maintain cruise rpm and only reduce throttle a little bit to avoid any shock cooling.

[Tupolev114]

I have found if i reduce MAP slowly at around 1 every 3 seconds till i get to 15in, and reduce to as low as 1500rpm depending on how steep i want to descend, I can get max just over 1000fpm down while not getting any shock cooling or the like but generally i will descend at around 500fpm from 150nm to 100nm from destination

[Medtner]

The rate of descent of the cabin pressure is the key here.

Early in the descent, from cruise altitude, you can drop down faster (remembering to keep the engine warm and happy, though). When getting closer to the airport you should aim to be low enough to be able to have 500fpm, give or take, for the approach. By that time the engineer have gotten the cabin pressure to such a point that your rate of descent is felt by the people in the back.

So in short - you can do faster descents when you have cabin pressure to work with. Check the gauges back there for reference - I do, and when it equalizes with my actual altitude I will need to be gentler. That works perfectly.

[CAPFlyer]

You should have no complaints for descent down to ~3000 feet MSL at 1000FPM or higher. The cabin can keep the descent for the pax well within spec. You should also be willing to accept the speed climb as you descend. I descend at cruise RPM and square the power and let the speed rise. I never get into the yellow this way, despite 1000-1200FPM descent rates. It also protects the engine from back loading too badly when the VFE shifts the blowers into LOW as you pass through 13,000 feet. Just make sure to give yourself about 5-10 miles of level flight before you start the approach to get the plane slowed down as you change to Approach Power (2300/23"). Then, I hold 23-25" MAP @ 2300 RPM on the glidepath and she'll find her way just fine at ~600FPM descent and the babies won't complain a bit.

[Gypsy Baron]

On descent you also need to be aware of the cabin altitude vs. the aircraft altitude. If you
descend too fast the aircraft altitude will 'overtake' the cabin altitude and from then on
the cabin altitude will descend at the rate the aircraft is descending and anything approaching
1000 fpm will evoke the chorus of babies crying.

When I fly I pretty much always take care of the FE functions and on ascent and descent I set
the cabin rate of change to 500 fpm instead of the VFE setting of 400 fpm. This allows me to
climb faster without exceeding the maximum differential pressure and descent quicker without
overtaking the cabin altitude. That is as long as I REMEMBER to set my descent cabin alt goal
when I have reached TOD

Paul

[Paughco]

You should have no complaints for descent down to ~3000 feet MSL at 1000FPM or higher. The cabin can keep the descent for the pax well within spec. You should also be willing to accept the speed climb as you descend. I descend at cruise RPM and square the power and let the speed rise. I never get into the yellow this way, despite 1000-1200FPM descent rates. It also protects the engine from back loading too badly when the VFE shifts the blowers into LOW as you pass through 13,000 feet. Just make sure to give yourself about 5-10 miles of level flight before you start the approach to get the plane slowed down as you change to Approach Power (2300/23"). Then, I hold 23-25" MAP @ 2300 RPM on the glidepath and she'll find her way just fine at ~600FPM descent and the babies won't complain a bit.

What he said. That's how I do it, although I usually pull power back to the bottom of the green arc and then start the descent. Larry the FE handles cabin pressurization during the descent while I fly the airplane.

Seeya
ATB

[Medtner]

This is one reason why the Connie is waaay easier than the Strat. The Strat needed much power to keep the cabin pressure in control. Hour-long descents resulted.

[addman]

This is one reason why the Connie is waaay easier than the Strat. The Strat needed much power to keep the cabin pressure in control. Hour-long descents resulted.

Indeed, I always do the FE stuff myself and the Strat was a real handful on descents. I can't say I miss those turbos. Connie is a dream in comparison, not easy but simpler.

[Alan_A]

Thanks, guys - great advice as always.

I'll have to keep better track of cabin rate of descent. I was always so cautious in the Strat that it never became an issue.

Yesterday I had a couple of very brief baby episodes in the upper reaches of a descent out of 15,000. It might have been that I simply overtook cabin rate of descent at that point, or it might be that turbulence (heavy at times) pushed me past the 1,000 fpm target. In any event I'll aim for more precision next time. As a general rule I like to keep the FE on the job (IRL I've always done a lot of delegating but it sounds like tweaking the pressurization settings on descent might be in order.

Does anybody know offhand the minimum rate of descent that default ATC will allow before it starts harassing you? As stated, there are things I like about it. On the other hand, if it doesn't mix well with propliner flight profiles, I'm happy to do without and go back to filing VFR or swapping in PF3. In general I'm starting to cut the modern trappings loose as I get more into the rhythm of Connie flying.

Thanks again, and thanks in advance for any ATC wisdom.

[Medtner]

Thanks, guys - great advice as always.

I'll have to keep better track of cabin rate of descent. I was always so cautious in the Strat that it never became an issue.

Yesterday I had a couple of very brief baby episodes in the upper reaches of a descent out of 15,000. It might have been that I simply overtook cabin rate of descent at that point, or it might be that turbulence (heavy at times) pushed me past the 1,000 fpm target. In any event I'll aim for more precision next time. As a general rule I like to keep the FE on the job (IRL I've always done a lot of delegating but it sounds like tweaking the pressurization settings on descent might be in order.

Does anybody know offhand the minimum rate of descent that default ATC will allow before it starts harassing you? As stated, there are things I like about it. On the other hand, if it doesn't mix well with propliner flight profiles, I'm happy to do without and go back to filing VFR or swapping in PF3. In general I'm starting to cut the modern trappings loose as I get more into the rhythm of Connie flying.

Thanks again, and thanks in advance for any ATC wisdom.

The ATC will need you to be faster than about 400 fpm. This probably depends a little on the speed as well. I try to aim for close to 1000 fpm when in IFR (before the cabin pressure needs to be concidered).

[G-BJPS]

Guys, if we change the cabin rate of descent ourselves to say 600fpm, and then enable the FE, will he change it back to 400?

Alan, 600fpm is the magic number to stop ATC harassment

[CAPFlyer]

The FE will change it back after a while, yes. But he doesn't set pressurization very often so it'll let you build up some separation if you're concerned about red-lining the differential.

Also, the IFR minimum climb and descent rate in the modern air traffic systems is 500 FPM. If you're VFR, that doesn't exist.

[G-BJPS]

Cheers CAP!

[Alan_A]

Alan, 600fpm is the magic number to stop ATC harassment

Ah! Good to know. I'll try that and see if it works as a happy medium.

Did well today with a VFR filing and a 500 fpm rate of descent, but obviously I wasn't putting ATC to the test.

One observation - I got the crying baby while on the glideslope, on final out of 2000 AGL with cabin pressure already equalized to outside air pressure. Rate of descent was 500 fpm, though it might have gotten a little steeper at a couple of points (heavy weather today, flew the ILS to minimums). Was the baby still reacting to pressure changes at that point, or is there a rate-of-descent trigger too?