ODP in CRJ
 

Keep hearing about using Direct/intercept
Page of FMS to help manage these descents
Please explain!!!

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.

Banana bar

At XJT we are taught to just follow the snowflake. The snowflake respects your most restrictive crossing fix

Banana bar only corresponds to the altitude in the preselect. That may or may not be the crossing altitude you need for an arrival or dept.

The snowflake represents the next altitude in the FMS. That may not be the ideal situation with multiple step downs on an rnav.

Both the banana bar and snowflake work, but the OP is asking about the way to see it all at once. Dir/INTC shows that.

Just curious, why did you lable this thread as "ODP..." To my knowledge ODP means obstacle departure procedure. Not trying to bust your cajones, just curious. Did you mean STAR?

Right. I just adjust the vertical speed to hit the altitude you don't have selected in the alerter.

It's all about technique. Like most things involving technology, there are 5 different ways to get the same outcome. As long as an FAR isn't violated it tends to not be an issue.

It also stands for Optimized Descent Profile, which if followed exactly allows for a Constant Descent, thereby saving fuel and negating the "step-down" and level off on an RNAV STAR with multiple step downs. An example wouldbe the TRUPS1 RNAV into DCA.

-2263

MEM, DEN, IAD/DCA, and other airports got them recently, I'm sure there's a lot more to come.

They're "the latest thing".

Seems as if they're like RNAV departures at times. Spend all the time briefing them and making sure the FMS is set up correctly, only to have the controllers break you off, assign a hard altitude instead of the window allowed, etc etc etc.

Oh, yep, you're right. Thanks!!

Add clt to the list as well...

I thought the advisory VNAV (snowflake) is not temperature compensated so its not reliable (in the CRj):rolleyes:

It works pretty slick when you only use it as ADVISORY. There are corrections shown every few thousand feet in a rnav arrival, but the Vnav calculations are normally within +/- 100ft of what you really need, or what would happen with auto throttles and full Vnav certification. Not bad for 1980's technology....

As speedbird said: Optimized Descent Profile

Not to bust your cajones, but your knowledge
Is lacking!!!!

The snowflake is for descend vias. Its amazing for those actually. The snowflake "looks through" all the at or above, and at or belows and guides you through them. At XJET we are taught that if you get a descend via, you set the next lowest "hard" altitude (not the at or below, or at or above, but the first "at" only altitude). When you hit that hard altitude keep setting the next "hard" altitude. Then you look for the TOD on the MFD, and when you approach the TOD, the snow flake will appear and you descend to match that. There is no vertical speed descent rate to follow to ride the snowflake down, you have to guess and see what allows you to keep up with the snowflake. A very common mistake is thinking the green data block on the PFD correlates to the snowflake, it does not. The descent angle and the vertical speed that is on the FPD (the green "data block") is ONLY for the the next hard altitudes on the FMS, and does NOT comply with the "at or above" or "at or belows" and will get you into trouble. If you follow the snowflake you will cross usually towards the top of the "windows" on the descent vias. You also have to watch the snowflake like a hawk to keep it from getting away from you. If you have a strong tail wind on a descent via while using the snowflake you have to be mindful of your groundspeed as use of the spoilers will probably have to be used as your descent rate can get high, especially if you have a slow down associated with your crossing restrictions on the descend via. If ATC vectors you off of the descend via, ALL the data and snowflake info goes out the window. ATC often is not aware of this, so you have to tell ATC that you need a new altitude to descend to, as you could get into trouble because the FMS does not know how to guide you down. You are now kind of descending into nowhere scenario.

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!!!

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.

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"

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.

Correct, MFD data shows decent rate to meet the next altitude. Following that can result in missing an altitude or speed restriction. Best example is MEM Tammy arrival landing north transition. There is a fix that has a soft window of 16000B/10000A. 2 miles later is a hard restriction of 10000 and 210 knts. If you follow the MFD data you will be 2 miles away from the 10,000/210kt restriction at 16,000ft. Following the snowflake will allow you to meet the altitude. Speed is on you. Flight spoilers likely required.

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

Please don't take my previous post as saying you were doing it wrong. Technique is individual to each pilot. Some guys set the hard alt in the FMS and preselect each step down and use the banana bar, some don't set the hard alt in the fms (leaving between and above/below), and use the snowflake, some set the hard alt in the preselect and use the banana bar and DIR/INTC page on the FMS to meet the restrictions. If your carrier doesn't "specify" it to be done a certain way and you don't bust an altitude, it's simply your technique. If you don't bust anything, your way works just as well as anyone's. The OP asked about the way of DIR/INTC, and I think he understands it. Obviously, with 2 folks up front, both "should" be very vigilant of where you are and where you are going on the "descend via" rnav arrivals. There are many "gotcha's" on some of those that require extra attention. The one that comes to mind is the eldee in DCA that throws a 10000 to 9000 step down.... The speed reduction and short distance between fixes can "bite" when trying to slow and get down if you get a little behind.

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.

There are a few CRJs out there that have a VNAV button on the flight guidance panel and when that is selected the flight director will give guidance to follow that snowflake. The FMS also expects you to enter the destination OAT and will present a CHK APT OAT caution if you don't provide an OAT prior to the FMS entering TERM.

I have to agree with you on the DIR/INTERCEPT page..... In a place like DCA with a strong west tailwind it will get you violated quickly..... If not it will leave you diving for the next fix on the ones in which are only very few miles apart.....

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.....

Can I claim target fixation? ODPs are burned into my head from my days as a II because nobody and I mean NOBODY had a clue how to depart an airpart IFR unless it was a published SID. So teaching ODPs was a crusade of sorts for me. Consider MY cajones busted and I will be TOTD.

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.

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

Ha!! :D Funny!

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.

Is it not OPD? Optimized profile descent?

So setting the lowest hard altitude, the snowflake will allow you to meet the at or above and at or below altitudes as well? I always thought the snowflake was looking at the next altitude in the FMS.

You need to have the correct VPA set on page three of the VNAV page. Every arrival/runway configuration has an optimum VPA, not just the default 3.0. But even then it's definetly not a "set it and forget it" descent rate so you can go back to your Maxim magazine or bitc#ing about the contract.

Very true. VNAV equipped CRJs will do it without modifying VPA though.

AWAC has computed the descent angles (VPAs) for all the OPDs we fly and have it available in our documentation so it can be entered when assigned. It works well except sometimes that angle hits the very top or bottom of a window...so you have to do some of that pilot Shiz Mav.

Thanks guys!

Beware the 50 knot tailwind.....

50kts? Kid's stuff. It gets fun in the winter when you've got 90-100 knots or more pushing you along :)

We have enough freaking acronyms in this industry do we really need to double up? ODP is obstacle departure procedure. Find a new one for whatever vnav crap you are trying to complicate.

Index>database>pilot waypoint list>delete the generic fixes>leave the smut ones

New CRJ-900s only.