Slam Dunk Descent Rates

[3WE]

A general question about airliner abilities to descend.

Ok, you are on a downwind at 10,000 feet AGL, "opposite your touchdown point and have virtually nothing between you and landing.

(It's a little unusual, but you guys have told stories of stuff like this actually happening from time to time).

So, can you "completely" cut power (typically) or do you need to carry some power for pressurization / whatever.

What kind of descent rate can you achieve (clean). (Just a rough range)

What kind of descent rate can you acheive with flaps, spoilers. (Just a rough range).

Or does it really all come down to comfort? (And what range of descent rate is that?)

[flyboy2548m]

I'll give you a general answer, since the question you asked is pretty general even for you: airliners can descend very quickly, if necessary. As for comfort, most pax can't really tell the difference between 3,000fpm or 6,000fpm. Heck, without looking at the gauges, even I can barely tell the difference.

Hope this helps.

[AndyToop]

...can't really tell the difference between 3,000fpm or 6,000fpm. Heck, without looking at the gauges, even I can barely tell the difference

Bet you could at 2000ft

[3WE]

...can't really tell the difference between 3,000fpm or 6,000fpm. Heck, without looking at the gauges, even I can barely tell the difference

Bet you could at 2000ft

There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

[PurduePilot]

...can't really tell the difference between 3,000fpm or 6,000fpm. Heck, without looking at the gauges, even I can barely tell the difference

Bet you could at 2000ft

There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Question of the day: 2000 minus 10% of 6000 equals how many feets?

[flyboy2548m]

There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Question of the day: 2000 minus 10% of 6000 equals how many feets?

Uh...1400?

[PurduePilot]

There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Question of the day: 2000 minus 10% of 6000 equals how many feets?

Uh...1400?

Good job.

[AndyToop]

...can't really tell the difference between 3,000fpm or 6,000fpm. Heck, without looking at the gauges, even I can barely tell the difference

Bet you could at 2000ft

There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Doesn't every level off start at 100% of your vertical speed?

[flyboy2548m]

Doesn't every level off start at 100% of your vertical speed?

Don't worry, Andy, 3BS is just posting whatever Gabriel sends him.

[PurduePilot]

[There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Doesn't every level off start at 100% of your vertical speed?

I think what he means is take 10% of your vertical speed and begin your level-off that much before reaching the desired altitude. If you're climbing at 3000fpm to 10000 feet, 10% of 3000 is 300 so you'll want to start leveling off at 9700 feet.

[AndyToop]

[There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Doesn't every level off start at 100% of your vertical speed?

I think what he means is take 10% of your vertical speed and begin your level-off that much before reaching the desired altitude. If you're climbing at 3000fpm to 10000 feet, 10% of 3000 is 300 so you'll want to start leveling off at 9700 feet.

I know what he think he means, its just never what he says!

[flyboy2548m]

[There's a rule of thumb- for a gentle level off, start at 10% of your vertical speed in fpm.

I don't know if it holds up at 6000 fpm descent rates, but if you start leveling at 2000, you will be done at 1300 and the customers would only feel several seconds of a slowing elevator.

Doesn't every level off start at 100% of your vertical speed?

I think what he means is take 10% of your vertical speed and begin your level-off that much before reaching the desired altitude. If you're climbing at 3000fpm to 10000 feet, 10% of 3000 is 300 so you'll want to start leveling off at 9700 feet.

Trying to arrest a 3000fpm climb rate in 300ft does not a gentle level-off make, trust me.

[PurduePilot]

Trying to arrest a 3000fpm climb rate in 300ft does not a gentle level-off make, trust me.

You'd definitely feel it, but if you did it perfectly smoothly and evenly over those 300 feet then it'd only be about a 0.065g acceleration, which is not exactly extreme.

[flyboy2548m]

Trying to arrest a 3000fpm climb rate in 300ft does not a gentle level-off make, trust me.

You'd definitely feel it, but if you did it perfectly smoothly and evenly over those 300 feet then it'd only be about a 0.065g acceleration, which is not exactly extreme.

You break my heart, Bradley. Out of curiosity, when was the last time you piloted an airplane that could do much more than 1500fpm upward? And before you say it, save your 787 sim adventures for you college buddies.

[PurduePilot]

Trying to arrest a 3000fpm climb rate in 300ft does not a gentle level-off make, trust me.

You'd definitely feel it, but if you did it perfectly smoothly and evenly over those 300 feet then it'd only be about a 0.065g acceleration, which is not exactly extreme.

You break my heart, Bradley. Out of curiosity, when was the last time you piloted an airplane that could do much more than 1500fpm upward? And before you say it, save your 787 sim adventures for you college buddies.

Sorry, I didn't mean to brake your hart--I sometimes forget that you are emotionally fragile.

You wouldn't feel prolonged vertical acceleration in a sim, so I fail to see how that would be at all relevant in this discussion.

[flyboy2548m]

You wouldn't feel prolonged vertical acceleration in a sim, so I fail to see how that would be at all relevant in this discussion.

You're right. So, how about answering my question?

[PurduePilot]

You wouldn't feel prolonged vertical acceleration in a sim, so I fail to see how that would be at all relevant in this discussion.

You're right. So, how about answering my question?

Oh, sorry, I assumed you were being rhetorical. I did some dual in a Piper Navajo three years ago and in a Seneca about two years ago. Now tell me why I broke your heart?

[flyboy2548m]

Oh, sorry, I assumed you were being rhetorical. I did some dual in a Piper Navajo three years ago and in a Seneca about two years ago. Now tell me why I broke your heart?

Good for you, Bradley. Next time you go up in the Navajo, try to "perfectly smoothly" arrest a 3000fpm rate in 300'. Let me know how it goes.

[PurduePilot]

Oh, sorry, I assumed you were being rhetorical. I did some dual in a Piper Navajo three years ago and in a Seneca about two years ago. Now tell me why I broke your heart?

Good for you, Bradley. Next time you go up in the Navajo, try to "perfectly smoothly" arrest a 3000fpm rate in 300'. Let me know how it goes.

So you're implying that inferior airmanship negates simple physics? Simple physics, of course, being very easy to add simple errors to at these early hours of the day, since it's actually a 0.13g downward acceleration now that I think about it.
Are you saying that it's impossible to change your vertical speed at a nearly constant rate?

[flyboy2548m]

So you're implying that inferior airmanship negates simple physics?

I'm just saying try it and get back to me. For the record, A/P on the CRJ when climbing at 3000fpm or more to 10,000' goes in the ALTS CAP mode (that's level-off mode to you) at just past 9,000'. So, good luck.

[PurduePilot]

So you're implying that inferior airmanship negates simple physics?

I'm just saying try it and get back to me. For the record, A/P on the CRJ when climbing at 3000fpm or more to 10,000' goes in the ALTS CAP mode (that's level-off mode to you) at just past 9,000'. So, good luck.

What are we arguing about again?

[flyboy2548m]

What are we arguing about again?

You said a 3000fpm climb rate can be arrested perfectly smoothly within 300'. I said try it and report back. Hope that helps.

[PurduePilot]

What are we arguing about again?

You said a 3000fpm climb rate can be arrested perfectly smoothly within 300'. I said try it and report back. Hope that helps.

I take "smooth" to mean "not jerky", and jerkiness is the third derivative of position with respect to time. Hope this helps.