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  • S-turns on final: how common?

    So I'm not a totally inexperienced traveler, but not on a plane every few days either. I've flown maybe 200 legs ever on commercial carriers.

    Yesterday I was on this flight from KDAY to KIAD: http://flightaware.com/live/flight/U...24ZZ/KDAY/KIAD

    The flight was generally uneventful, and as we neared Dulles we made some pretty tight turns which I did not find surprising in the vicinity of a busy airport. We got lined up on final, going what I perceived to be pretty fast and pretty low (< 3000 feet in my totally uninformed opinion), when all of a sudden the pilot does an "s"-turn! As he got lined up again at the end, I caught sight of the PAPI showing 4 white lights and a few seconds later we went around.

    I know something like that would be unremarkable if done by someone in a 172, but I've never experienced it before on a commercial flight. Is doing an s-turn on final considered acceptable practice in commercial passenger flying?
    Be alert! America needs more lerts.

    Eric Law

  • #2
    Sometimes an s-turn will help you with separation from a preceding flight, and instructions for it will be given by ATC.
    I would assume in the situation you described that they probably got vectored onto finals too high and the s-turn was an attempt to lose more altitude (initiated by the pilots or ATC, most likely the latter). When the pilots could not lose enough altitude during the s-turn (hence the four whites on the PAPI), they went around or were sent around for a second try.

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    • #3
      It's done frequently into La Guardia.

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      • #4
        I've never experienced s-turns in a commercial airliner, and in the Tomahawk I've done a couple as practice, but in practice when I needed to lose more altitude or increase spacing with a plane ahead in the pattern I did a 360.

        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
        --- Defend what you say with arguments, not by imposing your credentials ---

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        • #5
          Back when my local commercial airport was a busy, runway-starved hub, ATC would ASSIGN s-turns to airliners on final and well inside the outer marker sometimes when they were trying to get someone out.

          You probably experienced something that usually doesn't happen, but conversely isn't rare either.

          The other thing I remember were "takeoff" commands of "come up on your power/be ready" and perhaps even- rarely a command to start your roll....

          This was not takeoff clearance- and I think there was unspoken situational awareness- there's a plane getting real close behind you on final and I know the just-landed plane on the runway ahead will be off and clear in a few more seconds- so start your takeoff roll, I'll issue official takeoff clearance in just a sec, and if something bad happens you can gently apply your brakes and the landing plane can gently go-around (and hopefully it's not Boeing Bobby as it would be a very big deal to him).
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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          • #6
            Yeah I figured it was to lose speed/altitude, I was just surprised with all the recent emphasis on stabilized approaches that it was done so close to the runway. I didn't exactly have a stopwatch in my hand but I'd swear it was about 5 seconds between the end of the turns and when we crossed the threshold.

            The funny part was after we'd gone around (very quickly - to a different runway) and touched down, they got on the brakes harder than I've ever experienced in an airliner. The FA actually came on the PA afterward and said "And *that's* why we wear seat belts!" Anyhow I thought it was because they'd landed on a shorter runway but I looked it up afterward and all the runways at Dulles are 10,000 feet +/- a bit. So I think the pilot was maybe a little pissed off? That or he was just having fun with his "sporty" ERJ-145.
            Be alert! America needs more lerts.

            Eric Law

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            • #7
              Originally posted by elaw View Post
              Yeah I figured it was to lose speed/altitude...
              No!!!

              It is more intended to delay the arrival so a plane can depart or allow a landed plane exit the runway.

              I don't want to say "absolute never" to burn altitude nor to slow down, but I think it's more intended that I need a bigger gap in the arrivals to get a departure out.
              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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              • #8
                Originally posted by elaw View Post
                ...I was just surprised with all the recent emphasis on stabilized approaches that it was done so close to the runway...
                LOL!

                I tend to agree- you're supposed to be flying this beautiful ILS-nailed-constant-speed deal and here you go screwing it all up by hand flying and sight seeing the subdivisions underneath and along the final approach course...

                However, as Evan would recite there's strict definitions that kick in at 1000 and/or 500 feet that make you "stabilized" vs "unstabilized".

                And here's where you get into a nasty circular argument- Shouldn't a pilot with any sort of decent airmanship be able to pilot a plane from something other than the ILS??? (I mean c'mon- they need to fight turbulence, so certainly they can handle a little S-turn at 400 feet...right???).

                Counter-argument: Crashes kill people and deviations from SOP (including some painfully mundane deviations) have caused crashes before- so maybe we need to be crazy-strict about things.

                (And, all that being said is it ok to go S-turning at 700 feet? 1200 feet? Inside the outer marker???)
                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                • #9
                  Originally posted by 3WE View Post
                  LOL!

                  I tend to agree- you're supposed to be flying this beautiful ILS-nailed-constant-speed deal and here you go screwing it all up by hand flying and sight seeing the subdivisions underneath and along the final approach course...

                  However, as Evan would recite there's strict definitions that kick in at 1000 and/or 500 feet that make you "stabilized" vs "unstabilized".

                  And here's where you get into a nasty circular argument- Shouldn't a pilot with any sort of decent airmanship be able to pilot a plane from something other than the ILS??? (I mean c'mon- they need to fight turbulence, so certainly they can handle a little S-turn at 400 feet...right???).

                  Counter-argument: Crashes kill people and deviations from SOP (including some painfully mundane deviations) have caused crashes before- so maybe we need to be crazy-strict about things.

                  (And, all that being said is it ok to go S-turning at 700 feet? 1200 feet? Inside the outer marker???)
                  For some operators, in non-long-final approaches, the stabilized criteria is met if only minor control corrections are needed to keep the plane in the desired track (which can be curved) and the wings are finally leveled by 300ft AGL.

                  I don't know if that applies to S turns though.

                  In any event, 5 seconds before the threshold they would have been at some 100ft. Regardless the stabilized approach criteria, that's too low for my taste in an airplane doing 130kts, 700fpm and with a span of 60ft.

                  I'd like to see what MCM and BB have to say about this.

                  --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                  --- Defend what you say with arguments, not by imposing your credentials ---

                  Comment


                  • #10
                    Originally posted by 3WE View Post
                    No!!!

                    It is more intended to delay the arrival so a plane can depart or allow a landed plane exit the runway.

                    I don't want to say "absolute never" to burn altitude nor to slow down, but I think it's more intended that I need a bigger gap in the arrivals to get a departure out.
                    Well... I can't be 100% sure but I really got the sense it was to lose altitude. Per the PAPI we were pretty high, and I didn't see any other aircraft on or near the runway. Although I'll admit my eyesight isn't the greatest and the far end of the runway was ~2 miles away!
                    Be alert! America needs more lerts.

                    Eric Law

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                    • #11
                      Well Gabriel I'm pretty sure you can guess my sentiment on it :P.

                      First, general answer is no, its a silly idea.

                      However, I will leave a small 'out'. If it was being done relatively high for traffic separation purposes, then it 'may' be ok. If they're visual, up a few thousand feet, and the controller can see they need more separation that can be gained by a bit of a 'jink' that still has them back on final, stabilised, then perhaps.

                      I wouldn't be trying it in a large jet (just accept the go-around), but maybe in an E-Jet its more practical, I don't know.

                      I personally wouldn't be using one because I got high or fast - just put out everything that can drag, and if that doesn't work, go around. But then I don't fly an E-Jet.

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                      • #12
                        Originally posted by Gabriel View Post
                        ...In any event, 5 seconds before the threshold they would have been at some 100ft. Regardless the stabilized approach criteria, that's too low for my taste in an airplane doing 130kts, 700fpm and with a span of 60ft...
                        FWIW, the S-Turns I observed- while well inside the outer marker were not spectacularly low...I would guess (and it's just a guess) they were well above 500 feet, with their speed well maintained and using their eyes, altimeters, VASI, and ILS to keep on a dang good glideslope.

                        Superb airmanship, stabilized approach criteria met officially, exceptional landings without so much as a head turning.

                        By the way- I need to see if I can find an approach plate for an old LDA approach that the airlines used to do on our closely placed paralell runways....there was a localizer that was somewhat significantly off-set and you made a fairly low s-turn to line up with the runway.....

                        Actually I think I remember riding an LDA DMA and the final turn did turn heads....I seem to recall that you were required to wait till about 400 feet.
                        Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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                        • #13
                          That's actually what I thought it was at first! A side-step approach where they follow one runway's ILS most of the way in, then shift left or right and land on an adjacent parallel runway. That is, until the plane turned back the other way and got lined up again with the original runway.

                          I suppose in hindsight a side-step doesn't make much sense. I think approaches like that are used when an airport has multiple parallel runways but not all have ILS capability... or maybe when one of the ILSs is out of service. But I suspect Dulles has all the ILS hardware anyone could ever want.
                          Be alert! America needs more lerts.

                          Eric Law

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                          • #14
                            A sidestep is a very different thing to doing s-turns!

                            Sidesteps are relatively small heading changes, with a small change to the vertical path. If it is likely, it will be pre-briefed. It is one turn to intercept, and another turn to line up.

                            Similarly, a landing manoeuvre from an offset localiser is, again, a published, briefed, known procedure. Yes, the turn can sometimes be significant, and relatively low, but its all 'organised', and one turn.

                            S-Turns to lose height/speed are big turns involving a significant heading change (otherwise there is no point).

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                            • #15
                              Originally posted by MCM View Post
                              Sidesteps are relatively small heading changes, with a small change to the vertical path. If it is likely, it will be pre-briefed. It is one turn to intercept, and another turn to line up.
                              I'm hair splitting on you- accept my apologies.

                              The LDA approaches I recall had 2 to 3000 ft offsets. There was some decent maneuvering to get back on the centerline- I recall a lot of crisp bank changes...

                              Yeah, it was within the realm of competent, no-big-deal airmanship, and in the realm of fighting a good, crisp, gusty crosswind.

                              But that concept of "minimizing deviations" from a perfect 5 mile final with everything set, trimmed and aiming straight down to the landing point...it is a deviation and does require good ole Mark IV human alignment techniques with a fair number of nominal, last-minute adjustments, not all that different than turning a 1/4 mile final in a Cessna.

                              So...not a big deal, but then again so what if you are 20 knots fast and 200 ft high at some "gateway"....if you are ahead of the plane, you might be descending slightly faster and slowing the whole time to cross the fence perfectly "on the mark"....heck, no turns at all required for that case.
                              Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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