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This is all dependent on aircraft as well. You have an Optimized profile, a Crossing profit, and then there is a normal or comfortable profile (I made all of those up). I think most of anything other than RJ's use an ODP for an Idle descent. In the CRJ for example it's not really practical to do this when you have step down fixes and other things like tail winds. Idle decent in a CRJ holding a anything over 300KIAS is pretty aggressive and not comfortable for passengers. At least that has been my experience. Seems like rule of thumb is to descend at 3 degrees and it works well. Except for those short stepdowns and such.
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Originally Posted by Jetjock65:1340498
If you have altitude crossings for a dept/arrival the FMS will calculate for advisory vnav. this can be a crossing restriction of an assigned alt "5000", above 5000 "5000A", below "5000B", or between "6000/4000". The Vnav on the mfd will show the next altitude restriction only. If you hit "DIR/INTC" you will see all the Vnav calculations for the extire arr/dept. You can then use the most restrictive of all the points. It never fails that you see 1000fpm for a fix 30 miles out, but then 4,000fpm right after. From 30 out you may just have 1,500 to meet the end restriction. Obviously, you need to hit each "hard" restriction but it works well to show the overall path to assist planning.
Thanks Highney & RedVett Exactly what I was looking for!!! No need for any of the DIR/INTC info. Just will add to confusion. Level off til TOD, divide your ground speed by 2, and add a zero for your descent rate, then follow snowflake |
Originally Posted by Trip7
(Post 1340517)
The snowflake allows you to descend to a hard altitude at a constant 3 degree slope and meet all soft altitude windows. Some places like DCA the snowflake disappears after passing a fix during the descent which simply means to level off.
My ODP arrival briefing is simple and well.... brief. I will descend to the hard altitudes using the snowflake. Once I hit the TOD the snowflake appears, and I divide my ground speed by 2 to get my intial decent rate. I tweak it from there to follow the snowflake. The beauty of the DIR/INTC is you see the speed as well as the VS required for all the fixes, much like the legs page and MFD display, yet you also see the planned VS, which can be very handy if you have a "between" altitude followed by a speed restriction and continued descent. Obviously, if you are familiar with the arrival, you may already know the speeds by memory/familiarity and not necessarily need the extra info. So in the end, it's up to you. |
Originally Posted by lolwut
(Post 1340523)
I'm amazed a bunch of professional airline pilots are flying STARs using VNAV in an airplane that is not VNAV equipped... and calling said feature a "snowflake"
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Originally Posted by Trip7
(Post 1340527)
No need for any of the DIR/INTC info. Just will add to confusion. Level off til TOD, divide your ground speed by 2, and add a zero for your descent rate, then follow snowflake I guess with us I rather just put down the USA today and have the chart at and hit the lowest altitude for the specific fix we are crossing.... Then when there's the strong tailwind from the west we don't to worry about the ones with a good amount of altitude to lose and very few miles to do such..... Who knows we all have our different approaches. Unfortunately the software in the CRJ doesn't offer a great solution in which one is better then another..... To each their own.... |
What is taught at XJET is you have to set up the VNAV snowflake by going to the VNAV Decent menu and making sure that the Mach/indicated speed is set up correctly and the 3.0 degree is indicating as well for the descent.
Example: on some arrivals you have to read the STAR where it might tell you to maintain mach until transition to 280 maintaining that until reaching 10000 feet where you slow to 250. etc. then go to the PERF menue select Vnav, scroll throught the pages, where it is titled Vnav Descent, and plug in the numbers. should look something like this: .80/280 10000 250/10000 VPA 3.0 degree once that is set up the snow flake will guide you through all the at above and at below along with in between until reaching your hard alt. you need to make sure you take your ground speed/2 add 0. example: 200 GS/2 add o. 1000 fpm should keep you in line with the snow flake with a little adjustments..... |
Originally Posted by Jetjock65
(Post 1340493)
As speedbird said: Optimized Descent Profile
Not to bust your cajones, but your knowledge Is lacking!!!! |
FYI, the snowflake and the DIR/INTC vertical speeds do correlate. The most restrictive vertical speed is what the snowflake is giving you. My personal technique is to start a descent using the snowflake, then check the DIR/INTC page to see what vertical speed I need to hold the snowflake. Works like a charm.
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Originally Posted by block30
(Post 1340701)
Can I claim target fixation? ODPs are burned into my head from my days as a II...
Naughty By Nature - O.P.P. - YouTube |
Originally Posted by Boomer
(Post 1340708)
Here's a little video to help you remember all the FARs relating to "getting down with ODPs"...
Naughty By Nature - O.P.P. - YouTube Edit; I think I am still "old school" in thinking of CDA vs thinking ODP (continuous descent approaches). I believe the preferred terminology is ODP now. (??) Tried doing a ctrl F of the AIM, Instrument Flying, and Instrument Procedures Handbooks and couldn't find anything on CDA or ODP. |
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