Question for RJ drivers without VNAV

[JetMonkey]

I remember when I was at CoEx (now XJT) we were doing these "decent vias" ten years ago. They wern't the optimums but you still dialed down to the bottom crossing restriction as now. And as someone earlier mentioned, the old 3-1 worked just fine..

 

[Flyin2low]

I remember when I was at CoEx (now XJT) we were doing these "decent vias" ten years ago. They wern't the optimums but you still dialed down to the bottom crossing restriction as now. And as someone earlier mentioned, the old 3-1 worked just fine..

Did they have crossing waypoints every 4 miles that don't line up with each other? The 3-1 method still works because the design uses 2.2 degrees, but you would fly under the crossing alt unless you leveled off every 2.347543 miles.

 

[wms]

3:1 doesnt work because the glidepath changes from fix to fix. You risk missing a window.

 

[rjacobs]

Only the FAA would design something that is "optimized" yet is only a 2.2 degree angle. What is that optimized for? Certainly not fuel burn in a jet airplane unless you count burning more gas than necessary during a descent.

 

[JetMonkey]

Did they have crossing waypoints every 4 miles that don't line up with each other? The 3-1 method still works because the design uses 2.2 degrees, but you would fly under the crossing alt unless you leveled off every 2.347543 miles.

Maybe just a couple that were that close together. The 3-1 worked out fine and I always based it at about a 2000 fpm descent rate, give or take adjusting for a headwind or good tailwinds. These new optimums give a couple thousand feet window to allow for that which helps. To me its much easier now than before when everything was a HARD altitude restriction.

 

[JustaNumber]

Maybe just a couple that were that close together. The 3-1 worked out fine and I always based it at about a 2000 fpm descent rate, give or take adjusting for a headwind or good tailwinds. These new optimums give a couple thousand feet window to allow for that which helps. To me its much easier now than before when everything was a HARD altitude restriction.

I disagree that it's much easier now, but it's possible that I'm just not that smart. Take the FRDMM1 arrival into DCA for example. There are no less than 14 different altitude constraints. You can't assure that you will make every single one without doing 14 simultaneous descent calculations, or without just blindly trusting the "snowflake." Three are "at" altitudes, one is an "at or below," and one is "at or above," while nine are "between" altitudes, making descent calculations very difficult. There are some arrivals where you need to be at one end of the range or the other, in order to make subsequent restrictions, but that sure is difficult for me at least to figure it all out.

Also, the whole point is to have all the aircraft descending at the same rate and speed (to ensure good spacing), but with these altitude ranges, it is very possible some aircraft will be at the high end and others will be at the low end, where they will have very different ground speeds. I thought having just a few hard restrictions was much easier, and kept everyone at the same altitudes for the entire arrival.

 

[doh]

Pull up the Dir to page on FMS and it will give you descent rate for all crossing restrictions. Vert speed and your all set to make all restrictions adjusting vert speed as needed

That is what I did when I flew the RJ. Best way to make the cross. For the at or below/at or above windows, I change the altitude to the middle altitude. 13,000B/10,000A I set 11,000. Keep in mind that you may have a short distance between that last B/A altitude and the mandatory cross at the end of descent. And yes, the speed restrictions dick up the whole calculation! So be careful out there!

 

[doh]

I disagree that it's much easier now, but it's possible that I'm just not that smart. Take the FRDMM1 arrival into DCA for example. There are no less than 14 different altitude constraints. You can't assure that you will make every single one without doing 14 simultaneous descent calculations, or without just blindly trusting the "snowflake." Three are "at" altitudes, one is an "at or below," and one is "at or above," while nine are "between" altitudes, making descent calculations very difficult. There are some arrivals where you need to be at one end of the range or the other, in order to make subsequent restrictions, but that sure is difficult for me at least to figure it all out.

Also, the whole point is to have all the aircraft descending at the same rate and speed (to ensure good spacing), but with these altitude ranges, it is very possible some aircraft will be at the high end and others will be at the low end, where they will have very different ground speeds. I thought having just a few hard restrictions was much easier, and kept everyone at the same altitudes for the entire arrival.

They might want us all spaced nicely, but this scheme won't accomplish that goal. They will get what they are asking for, and not what they want!

 

[JetMonkey]

I go out on a limb and say that these "optimum" RNAV arrivals we're built with VNAV capable aircraft in mind. I'm based in PHX and that was one of the first places to use these arrivals. The engineers and flight managers from my airline built some of them and we used for testing these arrivals. Having a plane with VNAV makes all the difference I suppose. I'm on the Airbus, and fifi doesn't have too much problem handling them. Once and a while it'll bite ya, but if you keep monitoring, 9 out of 10 times you're golden.

 

[WMUSIGPI]

Too bad RJ's have taken over more than 50% of the domestic flying...