Aquasky18
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Southwest Airlines zig-zag manuever on final

Wed Jul 04, 2018 7:13 pm

So this weekend I travelled from SNA to LAS and back with Southwest since my usual carrier of choice (UAL) doesn't have direct flights. I enjoyed my flight and really appreciated the fact that Southwest Flight attendants go so far out of their way to make the trip fun for everyone by using humor and taking time to make light conversation with passengers.

I also noticed that Southwest seems to have some very talented pilots, who are fully comfortable maneuvering the aircraft both on the ground (they taxi much more rapidly than United) and in the air.

Anyway, on our approach to SNA, there was another aircraft (DL B737-800) in front of us. It was close enough in front of us to where I could clearly tell the aircraft type and carrier even though I just glimpsed it out my window as we turned from base leg to final. When we turned however, we didn't complete our turn on runway heading, rather the pilot flying continued turning (rather steeply) to the right until we were about 45 degrees nose right of runway heading. then he banked left, and turned to about 45 degrees left of runway heading, then back to the right again in a zig-zag pattern. When I looked out the window each time we turned back to the left, I could see the PAPI lights, and saw that we were above the glide path (4 white light with the innermost one slightly pinkish). After four steep turns in this zig-zag pattern, the pilot turned back to runway heading, pulled the throttles to idle, and pushed the nose down rather steeply (more than I've ever experienced). After the aircraft was re-established on glide path (I'm assuming), the rest of the approach and landing was completely normal.

My question is: what was the purpose of the zig-zag pattern after the turn from base-leg to final ? My best guess was that it was to create additional spacing between us and the aircraft in front of us rather than having to go-around since they looked too close to be clear of the runway by the time we touched down, but I've never experienced anything like it on United, or any other carrier I've flown. Is this a practice that is unique to Southwest? If not, what does ATC say that tells the pilot to initiate this maneuver, and how did we get vectored onto approach so close behind another aircraft in the first place?

Thanks in advance to any Southwest pilots, ATC controllers or anyone else with knowledge of this maneuver who can shed some light on my curiosity .
 
ilovelamp
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Re: Southwest Airlines zig-zag manuever on final

Wed Jul 04, 2018 9:44 pm

It’s not unique to Southwest but they statistically trend higher for this than other carriers. Why? Because they also accept and ask for visual approach clearances at a higher rate, too. That requires the pilots to maintain visual separation from the preceding traffic as opposed to ATC. So, what tends to happen is Southwest will turn base or final too quickly in hopes the preceding traffic is flying at a faster approach speed. To mitigate a go-around crews of any airline can ask for “S turns” on final to create the needed spacing like you suggest.
 
Woodreau
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 3:02 am

You can also see how far ahead the other aircraft is on tcas. You normally don't want to get inside 3 miles of the aircraft in front. Once you get inside 3 miles, atc tends to get antsy.

There are stabilized approach criteria that have to be met by 1000' agl (airline dependent) until you get below 1000' you can maneuver as necessary to get where you need to be vertically or laterally with the runway and other traffic.

Also Las Vegas can be relatively challenging if you're high and fast. The ground slopes up towards the 26s. So if you're relying strictly on the radar altimeter you'll end up configuring for landing too late
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Redbellyguppy
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 4:59 am

One way to manage energy if you're fat on it is to land flaps 40. However to slow to flaps 40 extension speed you have to level off and slow, since the plane doesn't really go down and slow down at the same time if you're fat on energy. This will make you high, however, you can descent quite rapidly at flaps 40 and as long as you can get back on profile by your stable approach criteria of 1000 ft to be on speed, on glideslope, sink rate less than 1000 fpm, and spooled, its legitimate.
 
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ikolkyo
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 6:41 am

Sounds like an S-turn and it is indeed to create some space. Definitely not unique to WN however.
 
mmo
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 11:47 am

Try flying into JFK during peak hours. Every operator would be proficient at doing s turns on final for spacing!!!
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ChrisKen
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 4:21 pm

mmo wrote:
Try flying into JFK during peak hours. Every operator would be proficient at doing s turns on final for spacing!!!

If large number of operators are having to perform 'S turns' for spacing, I'd be looking at re-training the approach controller.

ATC is there to provide a 'safe & efficient' flow of traffic. Cramming as many as you can down the approach, usually fails at the latter (& arguably the former).
 
mmo
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 6:31 pm

While that might be true as some airports, JFK handles a large number of foreign carriers. Sometimes, their speed control is a little lacking. It's not the approach controller, but the Thrust lever interface is the real problem.
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TWA772LR
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Re: Southwest Airlines zig-zag manuever on final

Thu Jul 05, 2018 7:43 pm

I flew in to SAN on UA once and we did this exact maneuver. It's quite quite a ride!
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BravoOne
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 1:42 pm

Old airline pilot saying. "There is no approach that can't be saved by a few steep turns" Followed up by a...."A pro would rather be dead than look bad" Gallow humor.
 
BoeingGuy
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 6:10 pm

mmo wrote:
While that might be true as some airports, JFK handles a large number of foreign carriers. Sometimes, their speed control is a little lacking. It's not the approach controller, but the Thrust lever interface is the real problem.


I don't understand this. All modern day airplanes by Airbus or Boeing have full authority Autothrottle/Autothrust systems (Boeing calls it the former; Airbus the latter). Doesn't matter if it's a foreign carrier or not. I don't understand how the Thrust Lever Interface on foreign carriers is the problem.
 
GalaxyFlyer
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 6:14 pm

The interface in question is the pilot/knob one; nothing to do with the automatics.

GF
 
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tb727
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 6:23 pm

Do Boeing airplanes do a form of groundspeed-mini like the Airbus?
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BoeingGuy
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 7:59 pm

tb727 wrote:
Do Boeing airplanes do a form of groundspeed-mini like the Airbus?


What is groundspeed mini? Boeing airplanes do display Ground Speed on the Navigation Display. That is calculated by the Internal system (IRUs).

There is no Autoflight mode on Boeing airplanes that track Ground Speed.
 
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tb727
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 10:05 pm

It's a calculated minimum ground speed on final once you are in managed speed mode(which is what we land in). It is based off the winds you put in from the ATIS and automatically bumps you bug speed up.
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Starlionblue
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Re: Southwest Airlines zig-zag manuever on final

Fri Jul 06, 2018 10:10 pm

tb727 wrote:
It's a calculated minimum ground speed on final once you are in managed speed mode(which is what we land in). It is based off the winds you put in from the ATIS and automatically bumps you bug speed up.


Nitpick: Ground speed mini starts with the ATIS wind entered in the PERF page. However on the actual approach the speed target is constinuously computed using winds experienced by the aircraft.
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tb727
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 1:13 am

Starlionblue wrote:
tb727 wrote:
It's a calculated minimum ground speed on final once you are in managed speed mode(which is what we land in). It is based off the winds you put in from the ATIS and automatically bumps you bug speed up.


Nitpick: Ground speed mini starts with the ATIS wind entered in the PERF page. However on the actual approach the speed target is constinuously computed using winds experienced by the aircraft.


Yeah, my GS mini dissertation was cut short by a toddler but I think the Boeing guy gets the drift.
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Max Q
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 6:07 am

Do you think that GS mini is a worthwhile feature as compared to ‘half the steady and all the gust’ max of 20 knots additive ?
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B747forever
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 6:37 am

ilovelamp wrote:
It’s not unique to Southwest but they statistically trend higher for this than other carriers. Why? Because they also accept and ask for visual approach clearances at a higher rate, too. .


What is the benefit of a visual approach? Why is it more common with Southwest?
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WPvsMW
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 6:49 am

It's "being your own boss", vs. waiting for instructions.
 
mmo
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 1:57 pm

Max Q wrote:
Do you think that GS mini is a worthwhile feature as compared to ‘half the steady and all the gust’ max of 20 knots additive ?


On a Boeing, with auto throttles engaged, you don't set the gust and steady state components. You set the desired bug speed and that is all.
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e38
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 5:06 pm

Quoting MaxQ (Reply # 18), "Do you think that GS mini is a worthwhile feature as compared to ‘half the steady and all the gust’ max of 20 knots additive ?"

MaxQ, yes, GS mini is very worthwhile. There is no computation involved at all. You simply enter the steady state wind from ATIS into the Perf/Appr page of the FMS and the authothrust takes care of everything.

e38
 
KingOrGod
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 7:10 pm

Woodreau wrote:
You normally don't want to get inside 3 miles of the aircraft in front. Once you get inside 3 miles, atc tends to get antsy.


Not this one :mrgreen: It is, however, controller dependent, but in the case of J following J and M following M I generally let the crews do as they please... I know for a fact 1.9nm on the same runway works :)
 
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tb727
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Re: Southwest Airlines zig-zag manuever on final

Sat Jul 07, 2018 7:11 pm

Max Q wrote:
Do you think that GS mini is a worthwhile feature as compared to ‘half the steady and all the gust’ max of 20 knots additive ?


I think it's a pretty neat feature, it's cool to watch it work. You can still add a few knots if you feel the need as well.
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Max Q
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Re: Southwest Airlines zig-zag manuever on final

Sun Jul 08, 2018 2:27 am

mmo wrote:
Max Q wrote:
Do you think that GS mini is a worthwhile feature as compared to ‘half the steady and all the gust’ max of 20 knots additive ?


On a Boeing, with auto throttles engaged, you don't set the gust and steady state components. You set the desired bug speed and that is all.



Depends,


On the 757 / 67 when performing a full autoland with AT engaged there is no need for a speed additive



However on a manually flown approach
autothrottles must be disengaged prior to the flare as they will not go to idle and the normal speed additive must be used



Haven’t flown the 777/ 787 but from what I understand the autothrottles are used all the way to touchdown whether flying manually or autoland and no speed additive is necessary
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mmo
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Re: Southwest Airlines zig-zag manuever on final

Sun Jul 08, 2018 7:30 am

Max Q wrote:

On the 757 / 67 when performing a full autoland with AT engaged there is no need for a speed additive



However on a manually flown approach
autothrottles must be disengaged prior to the flare as they will not go to idle and the normal speed additive must be used


I think if you look at the FCTM, you will find if you use autothrottles you don't have to use the speed additives. That holds true on a visual or a manual ILS. Obviously, you have to disconnect the autothrottles at the start of the flare as there is no retard on the A/T. However, I have never read or seen anything about adding the speed additives in those cases. On the 744/748, 777,787 you do have the retard function.
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Max Q
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 4:14 am

mmo wrote:
Max Q wrote:

On the 757 / 67 when performing a full autoland with AT engaged there is no need for a speed additive



However on a manually flown approach
autothrottles must be disengaged prior to the flare as they will not go to idle and the normal speed additive must be used


I think if you look at the FCTM, you will find if you use autothrottles you don't have to use the speed additives. That holds true on a visual or a manual ILS. Obviously, you have to disconnect the autothrottles at the start of the flare as there is no retard on the A/T. However, I have never read or seen anything about adding the speed additives in those cases. On the 744/748, 777,787 you do have the retard function.





That is not correct,


Once you’ve disconnected the autothrottles you no longer have any speed protection provided by that system


So it’s pointless to fly an approach manually using AT then have to click them off in the flare, you will then have no speed protection unless you choose to add it at that point !


The autoflight system, on the 757/ 67 unlike the 777 and more modern Boeing’s is not designed for this and since 1997 when I started flying the aircraft we have always
used the conventional speed additive for
wind when flying manually



On a full autoland (within wind limits) none is required of course as the AT’s will go to idle in the flare



Perhaps your operator has a different approved procedure



I can only speak for the major US carrier
I’ve flown the 757 and 767 for
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mmo
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 5:34 am

Maybe it is semantics. Let me ask you a question. If you were to fly the approach with autothrottles engaged at Vref with no additives and manually retard the thrust levers towards idle and simultaneously disengage the autothrottles, what is the difference between that and your limitation of disconnecting the autothrottles before the flare? Clearly, you aren't beginning the flare at 200' but more between 30'-50'.
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Max Q
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 6:54 am

mmo wrote:
Maybe it is semantics. Let me ask you a question. If you were to fly the approach with autothrottles engaged at Vref with no additives and manually retard the thrust levers towards idle and simultaneously disengage the autothrottles, what is the difference between that and your limitation of disconnecting the autothrottles before the flare? Clearly, you aren't beginning the flare at 200' but more between 30'-50'.



While I get your point it’s simply not
an approved procedure for us


And for good reason, autoland wind limits are significantly lower than manually flown limits


Of course that’s not an issue, when conducting an autoland you’re in a low visibility situation which means almost invariably there’s not much wind (if there was you wouldn’t have low viz )


The Older generation AT system on the
757 / 767 can easily cope with these lower wind conditions for the approach, flare and touchdown


Unlike the more advanced AT on more modern Boeing’s it’s not designed to cope
with much stronger, gusty winds on a manually flown approach to landing and Is not certified for that at my airline, or indeed in any scenario other than a full autoland



We don’t do that, interested to see if any one else does


I’ve seen the AT in use on the 777 and it works well all the way to landing on a manually flown approach (with occasional ‘encouragement’) but it was designed that way


I wouldn’t trust the AT on the 75/6 in that scenario, besides we’re not approved for it so it’s academic.
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mmo
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 10:26 am

First of all, I am not talking about an autoland. But I am talking about a hand flown approach using A/T. Dusting off the cobwebs, I seem to remember that was a technique particularly useful when going into a snow covered runway. I seem to remember doing that on a number of occasions during winter ops. But, I only flew the 757 for just about a year so it could be my feeble memory. My last flight on the 757 was in Dec 1985
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Max Q
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 11:32 am

mmo wrote:
First of all, I am not talking about an autoland. But I am talking about a hand flown approach using A/T. Dusting off the cobwebs, I seem to remember that was a technique particularly useful when going into a snow covered runway. I seem to remember doing that on a number of occasions during winter ops. But, I only flew the 757 for just about a year so it could be my feeble memory. My last flight on the 757 was in Dec 1985
The best contribution to safety is a competent Pilot.
 
Max Q
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 11:36 am

mmo wrote:
First of all, I am not talking about an autoland. But I am talking about a hand flown approach using A/T. Dusting off the cobwebs, I seem to remember that was a technique particularly useful when going into a snow covered runway. I seem to remember doing that on a number of occasions during winter ops. But, I only flew the 757 for just about a year so it could be my feeble memory. My last flight on the 757 was in Dec 1985




It appears you didn’t read my post


I discussed full autoland and flying a manual approach using the autothrottles
using my company procedures, addressing your post comprehensively


And respectfully, suggest you do the same.
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mmo
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 12:18 pm

I have. I suggest you might want to read my post. It appears you didn't.
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wnflyguy
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 1:46 pm

I've seen this done by Heavyweights into LHR all the time! So it's definitely not just a Southwest thing.

Flyguy
my post are my opinion only and not those of southwest airlines and or airtran airlines.
 
BravoOne
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Re: Southwest Airlines zig-zag manuever on final

Mon Jul 09, 2018 3:06 pm

There is nothing new or unusual about his maneuvering, other thna in todays ATC enviornment it's not applied as often as say in the previous years.

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