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  • Effects of wind shear

    In the next AAIB bulletin you will read of a heavy landing in G-CIZA, my latest Minisport. This is how I reported it to the AAIB (apologies for the capital letters but this is their requirement)

    AFTER A NORMAL TAKEOFF AND CIRCUIT PATTERN I LINED UP FOR A FINAL APPROACH AT IAS 60 MPH WITH FULL LANDING FLAP DEPLOYED. COMPARISON BETWEEN IAS AND GROUND SPEED BY GPS INDICATED A WIND OF 15 MPH AT CIRCUIT HEIGHT. THE APPROACH CONTINUED NORMALLY UNTIL I WAS OVER THE THRESHOLD OF RUNWAY 21 WHEN FROM AN ESTIMATED HEIGHT OF 20 FEET THE AIRCRAFT DROPPED UNEXPECTEDLY ONTO THE RUNWAY. THIS HARD LANDING CAUSED THE PORT SIDE UNDERCARRIAGE LEG TO SHEAR OFF. THIS RESULTED IN FURTHER DAMAGE. I OPENED THE CANOPY TO DEPART THE AIRCRAFT IN THE USUAL WAY.

    AFTER EXITING, I NOTED A COMPLETE ABSENCE OF SURFACE WIND.

    Assessment of the cause:

    LOSS OF AIRSPEED IMMEDIATELY BEFORE LANDING. WITH WIND AT CIRCUIT HEIGHT SHOWING AS 15 MPH (GPS CALCULATION) AND WITH AN IAS STEADY AT 60 MPH ON LATE FINAL I THINK THAT THE ABSENCE OF WIND AT THE SURFACE INDICATES WIND SHEAR AS A POSSIBLE CAUSE OR CONTRIBUTORY FACTOR

    I wondered if anyone else has had an experience of this kind? The aircraft is being transported to the Czech Republic for repairs by the way

  • #2
    Effects of wind shear

    Random thoughts......if circuit height is 500 feet plus, maybe even 1000 feet, what is the wind at this height to do with what is happening at ground level maybe a minute or so later ? But if you were observing adequate airspeed on the ASI all the way down final approach, that is to say a stable and well established flight path.......seems last seconds unpredictable wind shear caught you out. I've had a hard landing......but in my case was down to visual misinterpretation/spatial disorientation difficulty

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    • #3
      Effects of wind shear

      Patrick Burns wrote: Random thoughts......if circuit height is 500 feet plus, maybe even 1000 feet, what is the wind at this height to do with what is happening at ground level maybe a minute or so later ? But if you were observing adequate airspeed on the ASI all the way down final approach, that is to say a stable and well established flight path.......seems last seconds unpredictable wind shear caught you out. I've had a hard landing......but in my case was down to visual misinterpretation/spatial disorientation difficulty
      Yes, I was happy with the approach speed all the way down, allowing it to reduce to 55mph just over the threshold, the last time I looked at it. The stall speed of the aircraft is 40 mph, fully flapped, so higher than the average microlight.

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      • #4
        Effects of wind shear

        I do see this sort of thing as a bit of a problem with the lighter SSDR machines which while difficult would be good to address with type difference training of some form.

        I do not consider myself an expert pilot but I found it a challenge to step down from 390Kg machines to the SSDR machines and had to put a lot of effort into my approach to flying the smaller and very light machines so someone who has come from the Rotax 912 world would I guess have just as interesting time if not more so in adjusting to the type.

        The energy management and air control required in the light planes take you beyond the skill set you have for the more manageable heavier machines exactly like someone training on a microlight after flying the standard GA type of plane.
        I was talking to a fellow pilot who was of the same view having converted from GA and during the first few hours thought he had made a big mistake until he got into the swing and now is of the opinion that its the best thing he could have done.

        I believe we also need to factor in pilot age to the learning curve and be realistic as to how long it will take which has little to do with hours flown previously. The obvious difficulties of learning while in a single seater bring us back full circle in the training to the early days and I think the fact that the machines present themselves as little toys sort of gets us off on the wrong foot.

        I believe that SSDR will not have a problem with construction and design as most still use the guidance of Section S and so we have basically finished up with a French type of approval where the planes are self certified but we may have a problem with pilot error due to the lack of effective differential training being available.

        Glad you survived Rick
        Mick Broom
        Member 909
        Shadow G-MWTN

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        • #5
          Effects of wind shear

          Mick Broom wrote: I do see this sort of thing as a bit of a problem with the lighter SSDR machines which while difficult would be good to address with type difference training of some form.

          I do not consider myself an expert pilot but I found it a challenge to step down from 390Kg machines to the SSDR machines and had to put a lot of effort into my approach to flying the smaller and very light machines so someone who has come from the Rotax 912 world would I guess have just as interesting time if not more so in adjusting to the type.

          The energy management and air control required in the light planes take you beyond the skill set you have for the more manageable heavier machines exactly like someone training on a microlight after flying the standard GA type of plane.
          I was talking to a fellow pilot who was of the same view having converted from GA and during the first few hours thought he had made a big mistake until he got into the swing and now is of the opinion that its the best thing he could have done.

          I believe we also need to factor in pilot age to the learning curve and be realistic as to how long it will take which has little to do with hours flown previously. The obvious difficulties of learning while in a single seater bring us back full circle in the training to the early days and I think the fact that the machines present themselves as little toys sort of gets us off on the wrong foot.

          I believe that SSDR will not have a problem with construction and design as most still use the guidance of Section S and so we have basically finished up with a French type of approval where the planes are self certified but we may have a problem with pilot error due to the lack of effective differential training being available.

          Glad you survived Rick
          Thanks Mick, all part of the learning process.

          Edited to add: Interesting though that the wing loading of a "second generation" SSDR like the Minisport is about the same as a 912 Skyranger, about 40kg/m2 at MTOW, or maybe even a bit higher. Early SSDRs had the disadvantage of being very lightly wing loaded.

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          • #6
            Effects of wind shear

            As I say , I am no expert , the wing load may be the same as the heavier planes but there is a difference when you fly them possibly due to the inertia / mass relative to the gust loads.

            I know that if I come into land , lose all lift from the wing and land it is more than capable of taking off again and reaching a hight which would start to hurt all on its own. I observed the same effect on a hang glider landing just the other day and I am convinced that if I had a 912 Rotax strapped to my backside it would not happen ( at least in the same conditions ).

            I have no airspeed fitted to the plane and find it best to go with what the plane is telling me, I have never been able to take in and process information from the instruments when landing and with age it does not get any better. Being frail I concentrate on the hard bit outside the window to limit any pain and financial loss.

            You have experienced the early planes and must have picked up on the trick of diving it to within a few feet of the ground then sorting it out knowing that from a foot up you will still have some wheels on it if it goes pear shaped.

            Safe flying
            Mick Broom
            Member 909
            Shadow G-MWTN

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            • #7
              Effects of wind shear

              Crossing the threshold there’s a lot to take in visually and I wonder whether it would be worthwhile fitting a stall warning device to give an audible warning of a sudden loss of airspeed. If set up properly it should be ahead of a lagging ASI ?

              Glad you’re OK Rick

              John

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              • #8
                Effects of wind shear

                From my hang gliding days, we were always made aware of wind gradients and rotor effects at low level ready to catch you out and hurt you and pocket. So, its mighty important to increase speed through the approach, fly parallel to ground holding off, before flaring for a stand up landing. No ASI to tell you this, just your experience in practice. Wind socks, smoke from chimneys can give visual indication of what wind is doing on ground. Seat of the pants stuff really, to be visually aware of whats happening around you. All our electronic gizmos are turning us into airline pilots, without the benefits of long clear runways and high mass inertia.
                Glad your okay.

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                • #9
                  Effects of wind shear

                  Unfortunately wind is a funny old thing... it does NOT abide by any rules:-)
                  I fly from a small "postage stamp" on the exposed side of a hill in "the windiest place in Europe".. NE Aberdeenshire.
                  Some 9 years ago, when I first started flying from here, I put up 2 windsocks... one either side of my strip in order to "get a better idea".......................... result. 99% of the time they were pointing in totally opposite directions............. solution............... take em both down and decide which way the "wind was blowing" on each landing just before the threshold... not good... B***(*ger.. try the other strip..... still no good. go somewhere else.
                  As Mike says, please do not rely totally on gismos.... in such situations... degree of butt clenching is a better instrument
                  Glad you are ok Rick

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                  • #10
                    Effects of wind shear

                    Interestingly this morning is "calm" for here.
                    My "limp" windsock at some 5 metres agl is showing a "steady" wind from 230 deg, my anemometer at 10m agl and some 75m away from the sock is varying between 292 and 360 deg and a fairly steady 5 to 10 knots, with only +- 1.5 knot gusts at +- 20 degrees from the "steady state".
                    The wind turbines on the hill 1 mile to the east indicating about 270, the ones 3/4 mile to the South indicating 180 whilst the ones 1.5 miles to the SE are indicating closer to 180 and rotating significantly faster!

                    Bear in mind it is an exposed site surrounded by hills...:-)

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                    • #11
                      Effects of wind shear

                      But its Scotland , not a real place ;-)
                      Mick Broom
                      Member 909
                      Shadow G-MWTN

                      Comment


                      • #12
                        Effects of wind shear

                        Grateful for the observations chaps, and thanks for kind wishes.

                        One message I take is that in an SSDR with a highish stall speed it would be good strategy to have airspeed in hand. It is however easy to balloon an SD1 because of the difficulty of getting airspeed within a critical zone before flaring and settling due to lack of airframe drag/slippery design and major ground effect from ultra-low wing. Just a few surplus mph will muck things up. For me the other deterrent factor of surplus airspeed would be the short strip at 280 meters or so, so a critical touch down point.

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                        • #13
                          Effects of wind shear

                          Rick

                          Enjoy the plane and the challenge when it returns.

                          I am sure you will find it one of the best experiences of your life getting to grips with your new toy, it looks like a lot of fun and if I had some money would be on my toy to have list.

                          It took me 70 hours to consistently nail the Chaser which was the best thing I have done for a long time, lots of sideways out of control scary moments which took a bit of managing as I acquired the skill, all in easy stages, mind that was after a twenty year lay off so was a bit rusty ;-)
                          I even got to brush up my engine failure practice.

                          Fly safe
                          Mick Broom
                          Member 909
                          Shadow G-MWTN

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                          • #14
                            Effects of wind shear

                            hullo again Rick and returning to text of original post, there is the subject of calculating wind at circuit height using GPS/ASI.........whatever the aircraft track was at the time of your calculations, you would know only the headwind/tailwind component speed along that track at that height........it wouldn't inform you the actual wind vector, at any height. Hum,ho, is that right ? (I don't know).

                            I suggest that circuit height figure might just give an idea as to perhaps the best direction in which to attempt to land but not of any value as to what to expect on short final approach.
                            I have not read any words about a windsock so I presume there was not one there. As to what we might learn from this accident, you have written a few pointers today at 0958hrs.
                            There is also a saying..."set yourself up for for success"......and I turn my thoughts to how to do that. Well, there could be a pre-flight search for forecast surface wind at the landing spot, there could be an inflight search for nearest METAR, there could be a search for smoke indications in the immediate area, there could be a mobile phone call to a nearby contact, e.g fellow pilot, farmer, nearby garage, etc for local wind info. In the absence of any definite wind info and faced with the prospect of approach to land to a very short runway, there is the possibility to utilise the preplanned alternate destination.

                            And so on.

                            Rick you have written the idea to have adequate airspeed in hand on the short final, but mitigated by the need for the right speed at point of touchdown. With benefit of hindsight would you have handled the circumstances surrounding the accident any differently?

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                            • #15
                              Effects of wind shear

                              Whitehill Farm is too short! :-)

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