Windshear Whiplash on Final
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Windshear Whiplash on Final
I was really lucky in my ASW-27 at 70% CG when I had a windshear induced stall while moving to flap L at ~300 above threshold. I lost 269' and was fortunate to recover over lower ground before having to dodge a topsoil pile in the neighboring gravel pit.
Applying headwind component = TAS - GS, examination of the recorded flight data reveals 3 windshears, each over a 2 second interval, of -17, +23, -28 kt (application of Pythagorean sum of squares of a triangle on the final shear yields 6 kt of apparent headwind giving -34 kt -- twice the recorded wind of 17 kt).
Recovery action was flaps negative and stick forward.
The usual stall practice at 3000 AGL with a 1 kt/second deceleration has little resemblance to a low level windshear stall.
More details on:
https://www.dropbox.com/sh/lq9osn15b...wuYvScXya?dl=0
The more usual course:
The usual tendency is that the pilot must have screwed up somehow. Perhaps the real lesson is to maintain adequate margins, but when and how do we know extra margin is needed?
Always adding speed to get through a shear of twice the wind can make for long landings.
Applying headwind component = TAS - GS, examination of the recorded flight data reveals 3 windshears, each over a 2 second interval, of -17, +23, -28 kt (application of Pythagorean sum of squares of a triangle on the final shear yields 6 kt of apparent headwind giving -34 kt -- twice the recorded wind of 17 kt).
Recovery action was flaps negative and stick forward.
The usual stall practice at 3000 AGL with a 1 kt/second deceleration has little resemblance to a low level windshear stall.
More details on:
https://www.dropbox.com/sh/lq9osn15b...wuYvScXya?dl=0
The more usual course:
I watched one of those early ASW 20 fatal spins. It was from slow straight and level flight, not thermaling. The wing dropped sharply and the glider entered a conventional, nose-down spin. The recovery began almost
immediately (approx. 1/4 turn) but unfortunately there was not sufficient altitude (this began at approx. 300 ft AGL) and the pilot was killed when the glider impacted the ground slightly nose down (i.e., the recovery was almost
complete) but still sinking. Undocumented tail ballast was probably a factor... Pilot incapacitation due to dehydration may also have been a factor. The final blow, so to speak, was the lack of a headrest in this very early '20 and a battery pack behind the head that came loose. The pilot was an experienced, high-time competition pilot and instructor...
immediately (approx. 1/4 turn) but unfortunately there was not sufficient altitude (this began at approx. 300 ft AGL) and the pilot was killed when the glider impacted the ground slightly nose down (i.e., the recovery was almost
complete) but still sinking. Undocumented tail ballast was probably a factor... Pilot incapacitation due to dehydration may also have been a factor. The final blow, so to speak, was the lack of a headrest in this very early '20 and a battery pack behind the head that came loose. The pilot was an experienced, high-time competition pilot and instructor...
Always adding speed to get through a shear of twice the wind can make for long landings.
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RatherBeFlying
That is what scares me watching some pilots approaching at their VREF speed in very strong windshear conditions.
I landed a Citation in winter going into Doncaster the winds were 45 KTS gusting to 70 max 80 KTS at night.
Shop fronts were being blown in Lorries blown over as well as trees
Doncaster the winds were 10 degrees off the runway unlike Liverpool and Manchester.
the windshear down the approach was horrendous I was holding 170KTS but the IAS was leaping from 120 to 170 KTS with huge wing drops.
I held that speed till coming into very short finals and the air smoothed a bit flying it on at 120KTS instead of the usual 105 KTS
The worst bit was taxiing in as it took two of us to hold the controls
Shutting down the poor marshaller was blown clean off his feet.
This was the most challenging approach I have done but it emphasised that had I selected normal approach speeds and VREF the aircraft would have stalled. They were unforecast winds to that strength when we left and were almost identical at the alternatives albeit with a much bigger crosswind component than at Doncaster.
Remember with strong headwinds your landing distance will be much shorter so you can afford more speed on touchdown and learn to fly the aircraft on rather than a conventional flare and VREF doesn't not have to be 1.3 X the stall in a given configuration it could be 1.4 or 1.5 if you fly it on
Pace
That is what scares me watching some pilots approaching at their VREF speed in very strong windshear conditions.
I landed a Citation in winter going into Doncaster the winds were 45 KTS gusting to 70 max 80 KTS at night.
Shop fronts were being blown in Lorries blown over as well as trees
Doncaster the winds were 10 degrees off the runway unlike Liverpool and Manchester.
the windshear down the approach was horrendous I was holding 170KTS but the IAS was leaping from 120 to 170 KTS with huge wing drops.
I held that speed till coming into very short finals and the air smoothed a bit flying it on at 120KTS instead of the usual 105 KTS
The worst bit was taxiing in as it took two of us to hold the controls
Shutting down the poor marshaller was blown clean off his feet.
This was the most challenging approach I have done but it emphasised that had I selected normal approach speeds and VREF the aircraft would have stalled. They were unforecast winds to that strength when we left and were almost identical at the alternatives albeit with a much bigger crosswind component than at Doncaster.
Remember with strong headwinds your landing distance will be much shorter so you can afford more speed on touchdown and learn to fly the aircraft on rather than a conventional flare and VREF doesn't not have to be 1.3 X the stall in a given configuration it could be 1.4 or 1.5 if you fly it on
Pace
Last edited by Pace; 8th Jun 2015 at 11:39.
