Mr Rumbold

Not so much a technical questions as much as a technique.. didn't know where else to post it.

When you're flying a STAR.. do you put in the bottom altitude and follow the VNAV snowflake to ensure you hit the altitude windows? Or do you put in each lower altitude and do it "piece meal" as you go?

I fly the CRJ.. whenever I jumpseat (which is usually on a 737 or A320), they put in the bottom altitude.
Most captains I fly with on the CRJ, do it "step by step", setting the lower altitude of the next window and making sure the "banana" is just ahead of that fix.. which is how I usually do it.
I recently flew with a captain who put in the bottom altitude.. he showed me the technique, etc.. and it seems a lot better. I did it on my legs and had no issues whatsoever.. I know I won't be able to always do it because many captains will freak out and I won't have time or energy to explain what I'm doing (lol)

Just curious what others (esp CRJ drivers) do.

EMAW

I know in the ERJ, we would put the first hard altitude and follow the snowflake. Then step down each hard altitude. The reason being that if you are unable to couple the VNAV to the autopilot, it will not assure that you make the hard altitudes and it's even more work and attention to make sure you cross at the exact altitude. The airbuses/737s that you speak of are more than likely able to couple the VNAV to the autopilot. That ensures that you make the windows and the hard altitudes. There is no wrong answer, as long as you make all the restrictions. It's just a matter of how hard you want to work.

PerfInit

Since you are a CRJ driver, you know that the snowflake is "advisory" VNAV only. It is a great tool, IF you understand its limitations. Having said that, the CRJ does not have a true VNAV feature. I would NOT recommend the technique of setting the "bottom" altitude in a "descend via" arrival in the CRJ. If you do this, you are setting yourself up for an altitude bust. You have ZERO protection with this technique. All it would take is a minor distraction and you could be "off the path" in a heartbeat. Putting in each stepdown is tedious, but at least it offers some automation protection from an altitude bust. Just my $.02

HeavyDriver

Our airline's procedure.

If cleared to descend via the Star without an altitude assigned by ATC. You will put the bottom altitude in the Altitude Select Window and monitor the VNAV performance.

pokey9554

The CRJ VNAV snowflake is for guidance only and does not give you any altitude protection. My technique in the CRJ was to set the next altitude restriction, or the lower of the two if it's a between restriction, and put the banana just beyond the fix so you could keep the descent going without level offs if the restriction isn't hard.

The 737 has an actual vertical navigation mode similar to the NAV mode on the CRJ, except it tracks a vertical path. It will not allow the airplane to descend below the next restriction as long as the FMC is programmed correctly. It may allow the airplane to be high on the path, and that's where HeavyDriver's procedure comes into play.

I don't speak Airbus.

With a true VNAV, many operators set the bottom altitude and monitor the VNAV performance. Without a true VNAV, I would always set the most applicable next altitude.

rickair7777

In the CRJ the best technique is to use the Range To Altitude Selected, ie the magenta banana.

Approaching a fix, first set the top altitude (the at or below), verify the banana is at or before the fix. Then set the bottom altitude and verify the banana is at or after the fix. Adjust VS as needed.

Approaching the fix, and comfortable that you have it made, set the top altitude for the next fix. Repeat the process.

This way you can descend continuously in VS, with minor adjustments as needed, and have a clear visual depiction of where you stand relative to each restriction.

The more advanced technique (still precise but less visual) is to monitor the direct intercept page. This displays a VS to make each restriction, but it only displays the top alt if there are two restrictions at a fix. If you use the depicted VS or slightly more (basically cross pretty much at or slightly below the top alt) you'll also make the bottom altitude. This has the advantage that you can scoll down to see ALL the fixes and the VS required to make one. The early fixes might require 1000-ish fpm, but the final fix or two might need 2700 fpm, so this gives a heads up well before you get there. The banana won't tell you that until you set the altitude for the fix in question.

I don't use the snowflake for STARs, only for descent planning on visual approaches.

Mr Rumbold

That's what I do.. and it works.
Like I said- had a CA who uses the bottom altitude technique and follows the snowflake; I tried it and liked it- just have to monitor..
Also, adjust the descent angle (1.9, 2.6 or 3.5 I think) to make sure there are no level-offs (i.e. verify there's only a single Top of Descent point)
In the crew room, a check airmen said this is the ONLY acceptable method..... clearly it's not but, that's what he said)

I'm assuming the Airbus and 737 and 757 drivers I've jumpseated on always use the bottom altitude method because they have better Vnav guidance(?)

PerfInit

Excellent discussion. Comparing the CRJ FMS and Autopilot logic to Airbus or Boeing is Apples VS Oranges. They are all completely different. There is No VNAV button on the FCP in the CRJ. This alone should tell you something.

AboveMins

ERJ- no true VNAV. My airline tells us to set the first hard altitude, and continually monitor the descent, backing up with mental math. I like to keep the VNAV data page up during the descent, and verify crossing altitudes in the W/T menu of perf planning. This gives you an estimate of where you will cross within a window, and allows you to plan energy management a little more effectively... Not that it's really a problem in the ERJ, just good habit I guess.

EMAW

It's not necessarily a matter of better VNAV guidance. The other aircraft you speak of have a means to couple the VNAV to the autopilot. Meaning it will fly both lateral and vertical by itself. Add in the autothrottles and all of the pilots input can be done through the Flight Guidance Panel, except for pulling the spoilers/speed brakes which may have to be done to slow down while going down.