Mach Number Change Over

[scandinavian13 5,192]

 

 

Anyway. I really wasn't basing my technique (completely) on a single pilot. I didn't fully understand some concepts of VNAV so I asked, he told me that he always used LVL CHNG for climb and VS for descent. Just made me feel better about continuing to do that. (Though the beating I've taken here has me looking at VNAV again)

 

Yeah, there are a lot of airlines who use the concept of "well this is the way we've always done it." In SWA's defense, part of it was from operating a mixed fleet where some aircraft didn't have A/T, so they took the SOP of not using it at all. Still, be very cautious of not using something because one person, or one operator doesn't use it. Moreover, the sim is just that - it's a sim. If you don't understand something, try it out and watch it all come together. Both tutorials use VNAV extensively, so that should've been a good resource to avoid any confusion.

 

SWA isn't generally on the forefront of technology, which puts them in these weird SOP spots. That's not to say they don't have their act together - they just aren't usually on the cutting edge of technology or procedures. As an example, when I was on my last contract, we had two RNAV RNP approach examples that we wanted to get into place to relieve airport interaction pressures (put JFK on the ILS 13L and watch N90 go down the tubes; similar with ORD/MDW interaction). The curved approaches allowed a close turn to final, which kept the airports operating independently without sharing airspace. This, of course, requires the proper equipage and certification. JBU has been operating such an approach into JFK for years. SWA, since they still have some of the old 300s and 500s floating around, and will through a planned 2020, noted that they wouldn't update those older aircraft to be able to fly the approach into MDW. You can't blame them, really (especially since the primary benefactors were the ORD departures, and not SWA specifically, who'd be paying for the equipage/training for those approaches), but it definitely points to the priority they set in their business model, and that simply isn't being on top of the technological curves. There's nothing wrong with that, but if you're not facing the same constraints, I wouldn't be seeking them out as a model for behavior in the sim.

 

 

 

Not for nothing, though, but I would use the speeds on the climb page as targets. Reference, I guess. I knew they had no interaction with LVL CHNG.

 

Well, if you're wondering what VNAV does, you at least saw the mechanics of it by using its speeds. The only major part you're missing at this point is that those speeds are calculated as an "optimal profile" based on your PERF INIT entries. Additionally, it will obey an altitude restriction on a SID, whereas in FL CH you're having to manage all of that yourself.

[ALF1 15]

So Southwest because of their mixed fleet is in sort of a unique position and doing the right thing with teir SOPs, do they still operate -200's ?

 

I believe British Airways is also in the same boat. Do all Southwest airplanes have RNAV capability ? If not what is their SOP for RNAV approaches ?

[scandinavian13 5,192]

 

 

So Southwest because of their mixed fleet is in sort of a unique position and doing the right thing with teir SOPs, do they still operate -200's ?

 

Nope. The only older gens are the 300s and 500s.

 

 

 

Do all Southwest airplanes have RNAV capability ? If not what is their SOP for RNAV approaches ?

 

Any plane with an FMS/GPS has RNAV capability. As an example, I can fly an RNAV approach in a 172 if I wanted to. RNAV RNP is the issue here though, and in that case, the SWA birds do not have that capability last I checked.

[Spin737 102]

 

 

Matt, is there a reason for this? At this point, i guess, just a curiosity.

 

Reason for FL260? Dunno. But, that's around the altitude where you'll get the highest True Airspeed for a given CAS/Mach.

 

Not for nothing, though, but I would use the speeds on the climb page as targets.

That sounds an awful lot like VNAV. VNAV is just fancy LVL CHG that does levels offs that are in the box.

 

 

Here's how I roll:

TOGA to Vclean

LVL CHG to 3000 AGL

VNAV to cruise

V/S for lower climb rates for crossing traffic and for level offs, if the plane is climbing really fast.

VNAV for cruise

DESC NOW/ALT INT to initiate descents above FL350 (The 737 can overspeed up high in a VNAV idle descent.)

VNAV for most descents and STARS

V/S for smooth and shallow descents

LVL CHG for steep descents

 

That's just how I do it. We have U10.7 on our planes and can't do a VNAV takeoff, otherwise I'd do that, too.

[ALF1 15]

Nope. The only older gens are the 300s and 500s.

 

 

Any plane with an FMS/GPS has RNAV capability. As an example, I can fly an RNAV approach in a 172 if I wanted to. RNAV RNP is the issue here though, and in that case, the SWA birds do not have that capability last I checked.

Oops yes sorry, I meant RNP. I would have thought at least some birds had the capability and wondered how they SOPd the incommonality.

I guess they dont need it. Cant imagine AS without it though.

[cbrdriver 0]

Gentlemen, here's where I get twisted.

Piglt4 arrival:

HKUNA FL270

MTATA FL250

 

A good decent to HKUNA using VNAV, but after HKUNA, speed is commanded to 210knts (on the PFD) and she doesn't descend to MTATA.

 

What am I doing wrong?

(Same question as before to my friend)

[ALF1 15]

Can you post the airport you are flying into so we can look up the STAR please ?

[cbrdriver 0]

Sry, Alberto.

 

KMCO

[scandinavian13 5,192]

 

 

A good decent to HKUNA using VNAV, but after HKUNA, speed is commanded to 210knts (on the PFD) and she doesn't descend to MTATA.

 

Did you select FL250 prior to the T/D point, or after? It will only automatically descend if you select the next altitude prior to the T/D point. If you wait, you will have to press ALT INTV.

 

The fact that it's got you hovering on the yellow bar like that means it's trying to use energy compensation to make up some of the above-profile condition by allowing more of a buffer to pick up speed in a steeper descent. This in mind, the plane clearly wants to be descending (and knows it should be), but it's not being allowed to (in this case, by pilot action, or more appropriately inaction). Note that you're in VNAV ALT and not PTH.

 

Have a look at the tutorials to get a better understanding of VNAV.

[downscc 1,327]

Where else would have an arrival named for Piglet, the little bear's best friend?

 

What Kyle said. Always look at the FMA when you are asking the question, "Why is she doing this?" An airplane is better than a woman in this case because she will tell you... anyway, the VNAV ALT is exactly why you are not descending.  You expect either VNAV PTH or SPD.

 

I have flown the piglet arrival without problem so hang in there... you'll figure it out.

[ALF1 15]

AH yes Major, I missed that!!

 

John, further explaining what Kyle said, which is right on the money:

 

VNAV ALT will show up instead of VNAV PTH while in VNAV mode when there is a conflict with the calculated VNAV PATH by the FMC. It is usually an intermediary altitude in descent or climb. For example, if VNAV has calculated a climb schedule to cruise and suddenly you are told by the controller to hold present altitude you would press ALT HOLD on the MCP  and it would show up in the FMA Pitch (on the right). If the controller instructed you to climb to FL280 on an ammended clearance from a previous clearance for a direct climb to cruise at FL 360 for example, you would set your MCP ALT at 28000, the airplane would level off at that altitude. Because this is a conflict with the calculated VNAV PTH, you would get that annunciation in the FMA (VNAV ALT). This is the equivalent that you did arriving KMCO. You set 27000 (next alt restriction) in your MCP and the airplane leveled of while in VNAV mode to VNAV ALT. You had to set 25000 in the MCP shortly after acquiring FL270 to allow VNAV to continue in its VNAV PTH. If you did not set the altitude, it will hold what you set and the airspeed deal that Kyle said. Even if you set 25,000 in the MCP, but you are too late and the level off process has started after the altitude alert horn, you would further have to hit the altitude intervene button after setting the lower altitude in the MCP to allow VNAV to continue the descent to the new altitude.

[scandinavian13 5,192]

 

 

What am I doing wrong?

 

Additionally - I have to say thanks for the screenshot. It answered a bunch of my questions up front (especially since you have the SHOW THR LEVER POS function on, too), which definitely helped track the issue down.

[cbrdriver 0]

OK, so VNAV ALT on the FMA means it's holding an altitude in VNAV mode, while VNAV PTH will tell me that she's following the vertical path calculated by the FMC.

 

And during intermediary alt holds, I need to let the FMC know to continue the descent. It's not an automatic action.

 

I still had to read tutorial one twice before I caught that.

 

Thanks everyone for input.

[scandinavian13 5,192]

 

 

And during intermediary alt holds, I need to let the FMC know to continue the descent. It's not an automatic action.

 

Correct. Do keep in mind, though, that if you have an altitude constraint (e.g. "MULRR at 10,000"), you should set the MCP ALT to that value until you're approaching it. At that point - prior to crossing it, but reasonably sure the AP is paying attention to that value - you can roll the altitude down to the next constraint so that it never hits VNAV ALT and stays in PTH. In theory, you could immediately set the "bottom altitude" of the STAR (or "top altitude" of the SID), and VNAV would hit all of the constraints in between, but just in case, in practice it's good to set the intermediate constraints just in case the AP is acting up, or ATC needs to hold you at some intermediate altitude.

 

 

 

Thanks everyone for input.

 

Glad to help.