What Heavy jet will SWA buy?

[Golden Falcon]

My understanding is that VNAV doesnt attempt to maintain a speed on an idle descent unless it drops 15 it's slow and the AT wakes up
It calculates a path based on that speed and then flies that path- and it is a deviation from that path by X amount, that constantly changes vs computer perceived, programmed and actual reality, which will recalculate paths and revert to vnav speed once outside it's parameters.

Vnav will calculate a flight idle descent path based on the speed entered by the crew, weight of the airplane, and wind forecast entered by the crew, and any applicable speed constraints, the most common cause of speed deviations was the actual wind being different than the forecast entered by the crew, VNAV mode will activate the A/T when the speed is <15kts is correct, at least on the Boeing models I have flown..

 

[wood pecker]

Deleted rant

 

[Monkey Face]

More specifically, if like to know if Boeing does in fact produce several levels of vnav that operate similarly with different levels of performance

I believe there are two versions of common V-nav, full geometric path and partial geometric path. Southwest uses partial. When using partial, it may have a slight economy advantage. I was told one can change from full to partial with changes made on the CDU/MX prompt.

 

[Jim]

If you ignore GL and the other trolls, it can still be a useful discussion-
I am no self proclaimed expert Jim- and we're all too aware of those that don't have a great understanding of vnav. And rnp. And rnav. And lnav. And autothrottles. And iPads. And EFB's. And the -800 radar. And HF. And intl.

The list goes on my man-
This historically has not been a company that has embraced technology. IMO, GK is trying to change that and is meeting criticism from senior line folks from just about every department. He has stressed it- we have to use the latest in technology -

But to that end-
Our understanding is that not all boeing vnav operates exactly the same, and there is much difference within the internal guts of boeings top of the line vnav vs ours which is essentially one of the cheapest.
Is this rumor to you or how you understand it as well?
We have been taught when speed intervention can be used and remain in path- on approach essentially on an rnp -
And speed difference it will drop into vnav speed vs path-
I'm not all that studied up, just a dumb FO with a dozen competing interests- but I do want to understand this-
My understanding is that VNAV doesnt attempt to maintain a speed on an idle descent unless it drops 15 it's slow and the AT wakes up
It calculates a path based on that speed and then flies that path- and it is a deviation from that path by X amount, that constantly changes vs computer perceived, programmed and actual reality, which will recalculate paths and revert to vnav speed once outside it's parameters.

The last two are pretty simple and I'll acknowledge that there are quite a few who fumble a bit still-

But set me straight on the one above-

More specifically, if like to know if Boeing does in fact produce several levels of vnav that operate similarly with different levels of performance

In this case it more SWA Bubba than General Lee...

I've been told by Boeing instructors that the principals of VNAV are the same, how you implement/program VNAV differs by FMS/aircraft. But

- VNAV attempts to maintain optimum glide path. It will allow speed increases of up to +/- 15 KIAS to do so. Once the speed is greater than +/- from programmed, it drops out of path into speed.

- If you get the "drag required" FMS message, optimum glide path can not be maintained within the +/-15 KIAS speed constraint. You have to add drag to remain on path either through the use of flaps, speed brakes (or landing gear...) or a combination these. This is where , in my opinion, the SWA no speed brakes with flaps rule becomes a problem. Say you are doing an arrival with both speed and altitude restrictions and to fly that speed you need flaps to be above a minimum maneuvering speed. You get the add drag message. If you don't add drag, you do not descend at a rate great enough to maintain the path (next altitude restriction). Your speed requires flaps and is often above the next flap speed so more flaps are not an option. Now it is speed brakes or landing gear if you want to continue using a VNAV decent. I've seen SWA drop their gear 40 miles out of Vegas because of this. Talk about noise/vibration/pax comfort.... Of course you can always quit using a VNAV decent mode but then you lose all the advantages - mainly being if you keep the plane in VNAV Path you will meet all the arrival speed and altitude constraints of the published arrival (assuming you set up your FMS right).

- If you are not speed restricted, you can increase your speed on the VNAV descent page instead of adding drag if a greater descent rate is needed to meet an altitude restriction.

- Unless you are in the "on approach" mode, any speed intervention will drop it out of path and into speed mode. The approach phase is normally within about 12 miles or so of landing but it varies with each approach. You can determine if you are in the approach phase via your FMS. This varies with the FMS for example with the 767 Pegasus FMS we can tell on the route page. Worst case, always change your speed on the FMS VNAV descent page until right before the FAF (within 12 miles of the field) instead of using speed intervention.

- To maintain VNAV Path, make sure all your speed and altitude constraints are programed into your FMS. Unless a hard altitude is required, an "at or above" altitude usually works best because this allows the FMS to compute an optimum constant descent angle while meeting the final hard altitude requirement. If you want to slow or are given an assigned speed by ATC, change the speed on the VNAV descent page so the FMS can recompute a new path based on that speed.

- If you use "descend now", VNAV will initially set up a less than optimum slower descent rate until it intercepts the optimum glide path at which time it will increase the rate. If ATC gives you an early decent, use descend now vice flight level change if you plan on using a VNAV descent.

- Any use of the vertical speed mode will take you out of VNAV path.

Edit:

Vnav will calculate a flight idle descent path based on the speed entered by the crew, weight of the airplane, and wind forecast entered by the crew, and any applicable speed constraints, the most common cause of speed deviations was the actual wind being different than the forecast entered by the crew, VNAV mode will activate the A/T when the speed is <15kts is correct, at least on the Boeing models I have flown..

This too. If you think you will have stronger tail winds than predicted, you can trick the system by telling it engine anti-ice on. VNAV will then calculate its path using a higher idle thrust.

2nd Edit:
Speed brakes are not an "idiot stick" for use only when you screw up or when ATC screws you up. Speed brakes are a necessary tool for VNAV and should be used when needed without "shame".

 

[BILL LUMBERG]

Well done Jim.

 

[waveflyer]

Jim, I appreciate that - as said before there are plenty who do not understand what you just wrote and operate that way-
And we all know it- and usually the biggest perpetrators know it best
They just don't want to fly like that-
There certainly has been a resistance to change.

That said- we have been taught all that. In spades actually. The only parts I'll take issue with are that it will jump out of vnav path 15kts higher or lower.
I will have to see this and won't be flying til next week- but let me look-
15 kts slow doesn't take you into speed mode- it just wakes up the autothrottles until you're back on speed.
With our Smith FMC, this happens quite a bit at these "economical CI 20" descents-
I believe that I've been plenty faster than 15 kts and the only time I feel the need to slow it is if I'll over speed- in which case it will jump out of path and we don't feel shame in pulling the stupid stick-
I'm just going to keep using that term!
Bc I have to support Bubba on that particular one
Spoilers in a 73 don't add lift, they just steal energy that could be used- if you need it - ok- and a multiple step down rnav arrival like LAX will have your energy dictated to you anyway-
They aren't nearly as effective as they are on other transport jets
At 250 flight idle gets you 1200-1500fpm in thick air-
Add speed brakes and you get 1500-occasionally 2000.
It's just a little bit of help
Gear down gets you a lot of help for the ONT and ELP of the system
This is the first airline that will use gear more liberally as a drag device-
But I'm curious about your critique of no flaps and speed brake our maintenance has issued as a policy-

We operate over 700 737's and have been the financially strongest airline in our short history-
I've flown at 6 airlines and every last one of them has it's differences - both goofy and rational-
If SWA engineers say it costs us money to use them at the same time, I'm decently smart and I don't feel qualified to not comply- not my job in this role-
I do understand that pilots miss using that tool- but I can do a pretty good visual into ONT from NorCal and still comply-
We know the airplane won't disintegrate - we're just complying with a SWA restriction they say benefits our profits-

Again- ALL airlines have their goofiness-- and the same aircraft can often have significant differences in how they operate, and how those aircraft are set up.

So jim-

I'm Vegas based
As much as I hate that airport (in summer!)- 40 miles out- gear?
Where?
I used it 20 out flying from San Diego and landing 7R
Cumulogranite and all

I'll just end with- the 73 is not a 76. Especially re: speed brakes.
I go weeks on end flying our 9 legs a day and don't use them- I do when necessary but if If I happen to be paying attention- I won't need them
Usually when I do it's bc I have programmed a faster speed and PATH creeps up toward the red and not bc I planned on it

Otherwise it's an error on my part

I appreciate the discussion though
In all things technology here, SWA pilots need to hear it even if we know it bc there are so many of us that resist

Just allow for the differences Jim

Still looking for an answer to the different levels of VNaV produced by Boeing?

Many times it does seem to be programmed correctly and will just "recalculate" and pop into SPD on it's own-
I have attributed this to the inability to predict and program vertical movement of air and the Atari like speed of the Smith FMC (which is by far the goofiest, and worst FMS I've used)

(Bubba- how's this post for brevity??!! )

 

[SWA Bubba]

Did I hurt your feelings Jim, pointing out inaccuracies? Did you even actually read what I wrote? I thought I gave a rather polite reply to you (although I did give a "troll answer" to Gen'l Lee's "troll comment, however). Let me try this again, and I'll try to be as polite as possible:

In this case it more SWA Bubba than General Lee...

I've been told by Boeing instructors that the principals of VNAV are the same, how you implement/program VNAV differs by FMS/aircraft. But

- VNAV attempts to maintain optimum glide path. It will allow speed increases of up to +/- 15 KIAS to do so. Once the speed is greater than +/- from programmed, it drops out of path into speed.

This statement is true, but only true in 'idle descent' mode. It is specifically NOT true if VNAV is in 'geometric descent.' In that mode, once VNAV path is captured and the speed range window opens on your airspeed tape, it WILL maintain assigned vertical path at the expense of speed, by going fast if necessary.

- If you get the "drag required" FMS message, optimum glide path can not be maintained within the +/-15 KIAS speed constraint. You have to add drag to remain on path either through the use of flaps, speed brakes (or landing gear...) or a combination these. This is where , in my opinion, the SWA no speed brakes with flaps rule becomes a problem.

Again, since vertical glide path will be maintained by VNAV in 'geometric descent' mode regardless of airspeed required to do so, then what you're describing above would only be the case in 'idle descent,' which generally occurs only at altitudes where flap usage is either inappropriate or forbidden (>20k'). Additionally, if you are flying an assigned airspeed slow enough to require flap usage, you are clearly in the 'geometric descent' mode. In this mode, the "Drag Required" message alerts you that you cannot maintain your requested speed (you'll be fast but on path); it does not alert you that you cannot maintain your required vertical path. "Unable Next Altitude" alerts you to that.

- If you are not speed restricted, you can increase your speed on the VNAV descent page instead of adding drag if a greater descent rate is needed to meet an altitude restriction.

Very true, and this is exactly what I suggested instead of using the speedbrakes (my comment about not wasting the energy you've already paid for). Specifically, this is easy and generally not a problem during 'idle descent' from altitude, where ATC doesn't care as much about airspeeds.

This too. If you think you will have stronger tail winds than predicted, you can trick the system by telling it engine anti-ice on. VNAV will then calculate its path using a higher idle thrust.

This is a good technique, or you could just program in stronger than listed tailwinds (or lesser headwinds), and accomplish the same thing. Whichever.

Speed brakes are not an "idiot stick" for use only when you screw up or when ATC screws you up. Speed brakes are a necessary tool for VNAV and should be used when needed without "shame".

I never said "shame." I said that unless you've planned, programmed, or executed improperly (or unforecasted meteorological or ATC factors appear), then you shouldn't need to use your speedbrakes during a VNAV descent. I feel pretty comfortable saying that there is no VNAV system in the world that plans descents predicated on any speedbrake usage whatsoever. It would defeat the purpose of VNAV, which is to save gas. If you need to use speedbrakes to arrive at a given point on altitude and airspeed, then VNAV should have started the descent earlier to arrive at that point as assigned. You'd have saved gas by retarding the engines to idle earlier.

All this is predicated, of course, on your arrival having sufficient room to do this. There are places (the busy NE & New York areas, for instance), where airspace considerations and ATC procedures for aircraft saturation require less-efficient descents/slow downs, and you very well may need to use the speedbrake to comply with ATC speed/altitude demands. However, as a rule, arrivals are specifically designed to allow descents based on normal aircraft performance (engines at or above idle, no speedbrake) to save gas. That's why there's so many "at or aboves" rather than hard altitudes. ATC doesn't want you to waste gas any more than your company does. And you can be damn sure your company isn't going to buy software that requires you to waste gas on every flight.

Hey, as the pilot, you do what you gotta' do. You monitor what the computer is doing, and then do what you need to ensure compliance. All I'm saying is that in normal conditions, you shouldn't need to use the speedbrake to comply with a published descent. I'm also not denying that a lot of Southwest guys don't have a firm handle on VNAV logic and usage yet, because clearly that's the case. It also seems like you have a pretty good handle on it. However, unless you're just not explaining very well, you do seem to have a misconception about what happens, and what you can expect, in VNAV's 'geometric descent' mode.

Hope that was polite enough for you, and you don't think I'm calling you an idiot. However, General Lee can still kiss my a$$.

Bubba

 

[SWA Bubba]

Jim, I appreciate that - as said before there are plenty who do not understand what you just wrote and operate that way-
....... <most of this post edited out for brevity> .......

(Bubba- how's this post for brevity??!! )

I dunno, Wave, you're starting to post like me now. You're gonna' have a hard time keeping up your multi-thousand post count if you spend as much time as that on each post! :beer:

Bubba

 

[waveflyer]

Bubba,
Have you flown a Heavy jet?
The mass is different and an adjustment. Just like the 73 is an adjustment for RJ pilots.
I can think of a handful of rnav arrivals where speed brakes were common and necessary on the md11, but not on the 73.
That's where I've heard SWA pilots complain about these huge ranges of altitudes at some airports programmed into rnav arrivals (ie:EAGUL-PHX) - that range is necessary when you need to design an arrival that works for ALL aircraft.

What I do wish the smith box would do is show somewhere at what altitude it is planning on crossing those fixes that have altitude ranges or FLxxxA above - it's useful info

But just add that to my wish list for this FMS- (anchor point please)

 

[waveflyer]

I dunno, Wave, you're starting to post like me now. You're gonna' have a hard time keeping up your multi-thousand post count if you spend as much time as that on each post! :beer:

Bubba

I know right! haha
Cheers

 

[SWA Bubba]

Bubba,
Have you flown a Heavy jet?
The mass is different and an adjustment. Just like the 73 is an adjustment for RJ pilots.
I can think of a handful of rnav arrivals where speed brakes were common and necessary on the md11, but not on the 73.
That's where I've heard SWA pilots complain about these huge ranges of altitudes at some airports programmed into rnav arrivals (ie:EAGUL-PHX) - that range is necessary when you need to design an arrival that works for ALL aircraft.

What I do wish the smith box would do is show somewhere at what altitude it is planning on crossing those fixes that have altitude ranges or FLxxxA above - it's useful info

But just add that to my wish list for this FMS- (anchor point please)

Yes, I have flown heavies.

I've got about 2,500 hours in heavy Boeings, although it was before RNAV arrivals and descents were common.

And I agree that it's obvious that different aircraft have different flight characteristics. Arrivals are build using industry & aircraft manufacturer input for exactly this reason. That's why you see a lot of "at or aboves" (and altitude ranges) at step down fixes, with hard altitudes generally only near the bottom--to account for a variety of aircraft. The aircraft that have a harder time getting down are a lot closer to the published "at or above" altitudes during their descent, so they can make the hard altitude at the bottom. Conversely, the aircraft who can get down easier generally stay higher above those published "at or aboves" while still being able to make the hard altitude at the bottom. VNAV is all about every aircraft staying as high as possible, for as long as possible (that its model is specifically able to), so that everyone saves as much gas as possible. However using more energy to stay higher, beyond the point where you'll need to bleed off that energy with speedbrakes, is counter to this logic. Obviously it happens, but arrivals are designed to avoid this.

BTW, as far as your wish goes, you can accomplish that: if you delete the "at or above" altitude in the FMC, it will then change to show you the calculated attitude, in small font, that you'll cross the particular fix at during the calculated VNAV descent. Caution, however, if it's close to the assigned altitude, you might do well to enter it back in to protect yourself should conditions change.

Personally, my programming wish is that, when you're in 'idle descent,' and it does revert from "VNAV Path," to "VNAV Speed," that you get more than the those words on the panel with a 10-second box around it. Maybe a beep, buzz, or something. On the other hand, I guess that's why they pay us the big bucks--to pay attention to what's happening! :0

Bubba

 

[redflyer65]

Did I hurt your feelings Jim, pointing out inaccuracies? Did you even actually read what I wrote? I thought I gave a rather polite reply to you (although I did give a "troll answer" to Gen'l Lee's "troll comment, however). Let me try this again, and I'll try to be as polite as possible:



This statement is true, but only true in 'idle descent' mode. It is specifically NOT true if VNAV is in 'geometric descent.' In that mode, once VNAV path is captured and the speed range window opens on your airspeed tape, it WILL maintain assigned vertical path at the expense of speed, by going fast if necessary.

Again, since vertical glide path will be maintained by VNAV in 'geometric descent' mode regardless of airspeed required to do so, then what you're describing above would only be the case in 'idle descent,' which generally occurs only at altitudes where flap usage is either inappropriate or forbidden (>20k'). Additionally, if you are flying an assigned airspeed slow enough to require flap usage, you are clearly in the 'geometric descent' mode. In this mode, the "Drag Required" message alerts you that you cannot maintain your requested speed (you'll be fast but on path); it does not alert you that you cannot maintain your required vertical path. "Unable Next Altitude" alerts you to that.

Very true, and this is exactly what I suggested instead of using the speedbrakes (my comment about not wasting the energy you've already paid for). Specifically, this is easy and generally not a problem during 'idle descent' from altitude, where ATC doesn't care as much about airspeeds.

This is a good technique, or you could just program in stronger than listed tailwinds (or lesser headwinds), and accomplish the same thing. Whichever.



I never said "shame." I said that unless you've planned, programmed, or executed improperly (or unforecasted meteorological or ATC factors appear), then you shouldn't need to use your speedbrakes during a VNAV descent. I feel pretty comfortable saying that there is no VNAV system in the world that plans descents predicated on any speedbrake usage whatsoever. It would defeat the purpose of VNAV, which is to save gas. If you need to use speedbrakes to arrive at a given point on altitude and airspeed, then VNAV should have started the descent earlier to arrive at that point as assigned. You'd have saved gas by retarding the engines to idle earlier.

All this is predicated, of course, on your arrival having sufficient room to do this. There are places (the busy NE & New York areas, for instance), where airspace considerations and ATC procedures for aircraft saturation require less-efficient descents/slow downs, and you very well may need to use the speedbrake to comply with ATC speed/altitude demands. However, as a rule, arrivals are specifically designed to allow descents based on normal aircraft performance (engines at or above idle, no speedbrake) to save gas. That's why there's so many "at or aboves" rather than hard altitudes. ATC doesn't want you to waste gas any more than your company does. And you can be damn sure your company isn't going to buy software that requires you to waste gas on every flight.

Hey, as the pilot, you do what you gotta' do. You monitor what the computer is doing, and then do what you need to ensure compliance. All I'm saying is that in normal conditions, you shouldn't need to use the speedbrake to comply with a published descent. I'm also not denying that a lot of Southwest guys don't have a firm handle on VNAV logic and usage yet, because clearly that's the case. It also seems like you have a pretty good handle on it. However, unless you're just not explaining very well, you do seem to have a misconception about what happens, and what you can expect, in VNAV's 'geometric descent' mode.

Hope that was polite enough for you, and you don't think I'm calling you an idiot. However, General Lee can still kiss my a$$.

Bubba

Well said Bubba.

 

[Donald]

As a matter of fact, I am typed in the 737 and have flown the aircraft.

To stay in VNAV Path, you have to stay within rate of decent parameters and speed parameters. If you are not going to do so, you have to change something. The FMS alerts you to do this. If you don't want to add drag, another option is to change speed - unless of course you are speed constrained by the aircraft configuration, the arrival, the FARs or ATC.

The other common mistake I've seen SWA pilots do when trying to change speed to stay in VNAV Path is to do so by using speed intervention and then wonder why it goes to VNAV Speed mode. Unless you are in the approach phase within the FMS logic, you need to change the speed within the FMS and not set a manually selected speed. Any other time speed intervention automatically takes it out of VNAV Path.

It also always amazes me when I sit in a SWA cockpit, hear them brief a VNAV approach and then watch them start using vertical speed modes continuously.

If you see them revert to vertical speed mode, then they are no longer performing a VNAV approach. More than likely, they have reverted to a visual.

This has happened to me before, when ATC asks for a higher speed. Ie. 170k to the marker, when the VNAV wants you at 135k. If you have a tailwind on final, the 737 simply cannot slow down and stay on path at the same time. You must level off, slow, then throw out the remainder of your drag. Not only is the aircraft very slick, but Boeing didn't include enough parasitic drag in the gear and flaps.

If you saw one or more of our guys using vertical speed, after initiating a VNAV approach, this is probably why.

 

[waveflyer]

Was an honest question bubba

My heavy time is less than yours

Yeah, I did that once and a captain pressed execute on something he was looking at and thought he forgot to-
We fumbled, for the altitude bc the jet was aiming for the top altitude,
So I had to communicate better in the situation- (and it's every FOs pet peeve when a captain is typing all over the fms as non flying pilot... Works both ways I'm sure) but it would be easier if that planned altitude or speed was in small font below or beside

A lot to ask of an Atari I know
And I'm right there with you- it really ought to be an aural warn, though to Jim's point, it's been a good year since I've had PTH reverting to SPD surprise me-
Our group is better at anticipating now that we've been in this 1900's game for 4 years.
(They say a monkey will type out every word of Hamlet in order if given a typewriter and enough time )

Donald, I almost always change the speed at the FAF to 170, sometimes 180-185 for the 7 mile out ones-
I get better performance throughout the entire approach
-----------

HEY GL,
Is this all confusing you- I know you don't have much real world experience with these things- ms flight sim isn't actually real

 

[Jim]

Wave,

I have been in a SWA cockpit at least twice that I can remember on the KEPEC arrival to the 25s where the gear came out between IPUMY and NIPZO. 20 out going into SAN seems to be a regular thing.

If you have autothrottles, they should wake up if the speed gets close to 15 KIAS slow maintaining path. But when they go into throttle hold, it doesn't always happen (ala Asiana 214). Not waking up happens occasionally on the 767 going into LAS. In this case, VNAV will drop from Path to Speed as the logic says +/- 15 KIAS. Same thing applies if the autothrottles are inop and you don't manually add power. VNAV logic is not dependent on autothrottles.

I do not know if there are different VNAV levels but the Boeing instructor I talked with said the principals were the same for all FMS/aircraft, it is the application that is different. Hawaiian 330 pilots use the same principles as I do in the 767, they just program their boxes/push their buttons differently.

And please, go back to using complete sentences....

SWA Bubba,

If the speed is close to the +15 KIAS range, I will get a "drag required" message to tell me to add more drag to increase my rate of descent. If I don't add the drag, then I will drop into VNAV speed as the speed continues to build as the rate of decent increases to hit the next required altitude.

Now in VNAV Speed and the FMS determines that the rate of descent can not be increased enough to hit the next altitude, then I will get the "unable next altitude" message. (I'll also get this message if I have my VNAV Descent speed set as high as possible and the aircraft can not descend at a great enough rate due to speed limitations which the autopilot will not exceed.)

The bottomline is that as long as I keep it in VNAV Path, I will make every altitude and speed contraint on the published arrival/approach. The easiest way (and the Boeing way) is to use speed brakes as required. The first time I ever did VNAV was for my 737 type and it was Boeing instructors teaching it at a Boeing training facility. I figure if the aircraft manufacturer says you can/should use speed brakes with flaps, then it is okay to do so. Further, as far as I know SWA is the only one with this self induced limitation. Is there some secret SWA knows that the rest of us don't, or is this a case of someone in power once saying "I believe this causes....so don't do it" and it becoming fact instead of one man's opinion?

I will grant there are some aircraft where there are limitations on the use of speed brakes with flaps. I believe it was prohibited in the DC-10 because it caused excessive roll rates but it's been 15 years since I looked at the DC-10 limitations and I'm not 100% sure on this.