(Stupid) E-Jet questions

[jtrain609]

I teach the system. I understand it very well. If you leave (properly programmed) constraints alone, the system will find the optimum time to descend for whatever angle you program. It will descend at a constant rate through the constraints to the final restriction. It's very smooth, and very stable. If you change the constraints it levels off early, then descends again to the next constraint, depending on how you program it. There's a reason they put at or above altitudes in there.

Obviously you have to take wind and engine A/I into account, but the best way to do that is with descent angle changes. So program a 2.5 decent angle, and it will slow down and go down. There are some arrivals where you have to pay very close attention, like the KRANN arrival into Boston when landing on runway 27. But if you make altitudes hard on that arrival, it will be much like a football bat...effed up.

So, let me just point one thing out real quickly.

The box is the box. The box is not the airplane. I've had instructors tell me things like, "The VNAV ALWAYS works perfectly!" and "FLCH NEVER chases a speed!" While these things may be true in the box, I've found them to have exceptions in the plane.

FLCH, when heavy, is asking for pitch oscilations in the 30's. Will you get to your desired cruise altitude in FLCH? Sure. Will it be smooth? It depends. Is keeping the plane in FLCH the best course of action? It's probably the safest from the standpoint of stall protection, but I'm not positive its the best solution. We climbed in VS in the -145, is that solution reasonable in this thing?

To a lot of instructors it's not, because the point is moot; to them, FLCH never hunts for a speed. So the discussion, to a sim instructor, is really about how the trainee is advocating getting themselves killed when they stall out in the climb.

 

[flyinggreasemnky]

I think you guys are also talking about two different aircraft, utilizing the same autopilot.

From what I've been told about the 190, is that it is much easier to handle in conjunction with the FMS. Whereas the 175/170 is constantly playing catch-up. Hence why @ClarkGriswold is advocating "futzing" with the VNAV profile. Where as, again so I'm told, the 190 will do just fine in that profile.

I haven't flown since epic load 23.1 so I'm not sure if the 175 flies the FREDM or KRAHN any better than when I did it last. By the sound of it, it doesn't.

The only real difference between the 170 and 190 is that the 190 is much cleaner and doesn't like to slow down so, you have to change to an even shallower descent angle. The FRDMM2 should have the descent angle to 2.0 (make sure the descent speed is at least 280 as well) and you will have no problem with smoothness or passenger comfort on the 170. Due to it being such a shallow angle, it even works on the 190 for hitting the speeds. I've flown both and seldom have to use the spoilers. Typically, they only come out if you have a tailwind greater than 50 knots.

Messing with setting hard altitudes will really screw up the VNAV quickly as it has to recalculate more and will end up diving a lot and over speeding in the dive. I've watched guys do that under 10,000 and speed up to 265 quickly because they weren't ahead of the dive they created. BTW, I usually adjust the descent angle to 2.5 just to make it easier to hit speeds when not on an optimized descent arrival.

 

[PhilosopherPilot]

So, let me just point one thing out real quickly.

The box is the box. The box is not the airplane. I've had instructors tell me things like, "The VNAV ALWAYS works perfectly!" and "FLCH NEVER chases a speed!" While these things may be true in the box, I've found them to have exceptions in the plane.

FLCH, when heavy, is asking for pitch oscilations in the 30's. Will you get to your desired cruise altitude in FLCH? Sure. Will it be smooth? It depends. Is keeping the plane in FLCH the best course of action? It's probably the safest from the standpoint of stall protection, but I'm not positive its the best solution. We climbed in VS in the -145, is that solution reasonable in this thing?

To a lot of instructors it's not, because the point is moot; to them, FLCH never hunts for a speed. So the discussion, to a sim instructor, is really about how the trainee is advocating getting themselves killed when they stall out in the climb.

Anyone who teaches (or even thinks) in absolutes is an idiot. VNAV does okay most of the time, but there are scenarios where you have to help it out. FLCH does actually pretty well compared to "speed mode" on the CRJ, but again, not always.

In theory, you'll never get debriefed for a "technique," but it's a constant struggle for any instructor to keep in mind that your technique isn't THE technique.

I debrief people when their technique can lead to confusion or TEM problems, just so they are aware of the threats, but as long as it isn't prohibited, they are free to fly as they like. But here at Blue you can fail a check ride for a TEM error, so that's a big difference compared to many carriers.

 

[PhilosopherPilot]

Messing with setting hard altitudes will really screw up the VNAV quickly as it has to recalculate more and will end up diving a lot and over speeding in the dive. I've watched guys do that under 10,000 and speed up to 265 quickly because they weren't ahead of the dive they created. BTW, I usually adjust the descent angle to 2.5 just to make it easier to hit speeds when not on an optimized descent arrival.

Yup. That's why it's a bad idea in general to make the altitudes hard. It's not prohibited, but it isn't a good technique. There are other methods that accomplish the same goal without futzing with the VNAV logic. What Clark was talking about earlier I don't consider the same as messing with intermediate constraints, since he was just talking about making the fix prior to the final fix a hard altitude. All that does is moves the bottom of descent back a few miles, which is functionally the same as creating a Place Bearing Distance fix prior to the final restriction.