X-ing restrictions

[pianoman]

Yeah I don't understand why people hate any descent over 2000 FPM. If you look at the pressure controller, the cabin is still descending at the same rate. As long as you roll the VS down smoothly, I think that's probably the most fuel efficient and quickest way to go. If you start down way early, your TAS drops and you can back up traffic on the arrival also.

That said it's just my technique. If the FO wants to do something else and it's not a safety/ATC issue, more power to them as long as it works.

 

[DrunkIrishman]

I use the FMS. Once it says about 2000 fpm I start to descend so that the deck angle in the cabin doesn't get too steep for the pax.

If the FMS is not an option, I multiply the alt to lose by 3 and take half of the GS and then add a 0 at the end to figure out my rate.

Alt: 37,000
Cross@10,000
GS: 500 kts
Alt to lose is 27,000 x 3 = 81 nm
1/2 of GS is 250. Add a zero to the end and you get 2500 fpm.

You will have to adjust your rate of descent when your GS changes, which it will...first it will increase, then it will decrease as you get lower in the atmosphere.

BTW, this also works for glideslope reference on an ILS. Instead of chasing your ball up and down, use the VSI as a lead reference. If you are flying at a GS 140 kts, then you should have a VSI showing 700 fpm (140/2 = 70, add a 0 to the end to get 700). If your VSI showed 500 fpm, you would know to push the nose down before your ILS ball started to move down.

 

[91100 100 set]

Okay, I'll bite.

(GS*desired slope angle*1.77)=the EXACT descent rate you need. Work it anyway you like. You want to desend at 2500 fpm? Divide that descent rate by your 1.77, then divide that number by your GS (remember that your GS will likely change with the wind and TAS changing in the descent), and presto, there's the angle to plug into your FMS.

No FMS? Then use the "times 3" rule and don't get too worked up about it, you're probably not flying an airplane where getting down to a crossing restriction a bit early will cost you much extra fuel anyway.

If we can't cowboy in these airplanes, we might as well occupy ourselves somehow. This is how I occupy myself, by being a nerd with the calculator in my shirt pocket.

 

[LAXSaabdude]

I used to use the ALT to lose * 3, GS * 5 to make crossing restrictions in the EMB-120, however this can lead to descent rates of 3000 fpm or more in the ERJ.

Actually, if you are descending correctly (i.e., flight idle descents), you should be looking at about 3000 fpm on the descent. That is normal, and, despite what some people may tell you, much smoother.

I watch some guys try to maintain a 2000 fpm descent, and they keep bringing the thrust UP AND DOWN AND UP AND DOWN AND UP AND DOWN....I'm sure the poeple in the back just love it.

Bring it smoothly back to idle, roll the VS to 3000, and just leave the thrust parked at idle. Quiet, smooth, and efficient.

LAXSaabdude.

 

[LAXSaabdude]

some of you guys sound like you're saying 3000 fpm or descent is a bad thing.. it's a jet. flight idle, or at least very low thrust ain't gonna shock cool the motors, and it saves gas, keeps you on the required glide path etc etc.

Yup, 'zackly. Fly it like it's meant to be flown. You're not flying a 402 anymore.

LAXSaabdude.

 

[CitationLover]

isn't a 1.00 epr descent the "best" descent?

 

[pianoman]

What reasons would make that the "best" descent, in your opinion? Honest question- our plane has N1, no EPR. I've always heard, at least with our jets and CAL's, that a flight idle descent without boards is kind of the holy grail. Up at altitude as long as possible, going fast and sipping gas.

 

[five-alive]

if you use your altitude times 3 that will give u a 3 degree glide path, it is up to you to maintain that. i use gs divided by 2 for rate of descent. But honestly, even if you are doing 3000fpm, so what? Back in my lear 35 days( running on fumes) we would do idle throttle descents giving us an 8000fpm descent no 3 to 1... a 1.5 to 1 is what we would use. most fuel efficient type of descent is idle throttle as long as you start it at the right distance.

Thrust idle gave you 8000 fpm? Yikes, I hope that was with spoilers. Otherwise that would be an aerodynamic equivalent of a brick with bricks for wings

 

[CitationLover]

What reasons would make that the "best" descent, in your opinion? Honest question- our plane has N1, no EPR. I've always heard, at least with our jets and CAL's, that a flight idle descent without boards is kind of the holy grail. Up at altitude as long as possible, going fast and sipping gas.

look i admit i'm ignorant in regards to this, hence the question.

however, i thought a 1 epr would be the most aerodynamically clean descent (ie the thrust output would equal the drag caused by the fan blades). i dunno though.