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Close one at Frankfurt

Old 3rd Sep 2023, 03:22
  #21 (permalink)  
 
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Eyeballing the QAR traces, there's a ≈2 second spike in the AoA topping at 20.92. I suspect a vertical updraft pivoted the vanes entering the updraft. It would take ≈1 second before the entire 55m of aircraft would be completely in the updraft. The graph eventually shows AoA stabilised at -10, which raises the question of how well the vane position in the graph is calibrated to wing AoA.

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Old 3rd Sep 2023, 22:58
  #22 (permalink)  
fdr
 
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Originally Posted by RatherBeFlying
Eyeballing the QAR traces, there's a ≈2 second spike in the AoA topping at 20.92. I suspect a vertical updraft pivoted the vanes entering the updraft. It would take ≈1 second before the entire 55m of aircraft would be completely in the updraft. The graph eventually shows AoA stabilised at -10, which raises the question of how well the vane position in the graph is calibrated to wing AoA.

presenting time domain data on a distance X axis is somewhat unusual and can lead to odd assumptions. Normally the AOA probe has Kalman filtering for short period damping of the output for displays, however that is system dependent if the DFDAU is picking up raw or filtered data. The data also has biases that are applied to correct raw sensed angles to present AOA relative to flap geometry, and IIRC, normally that is the data that is picked up by the DFDAU, which would suggest it is filtered.

As far as a "spike" from an up draft, that presumes a... 20-30 m/sec vertical rate from some source at low levels, and what the source of such a flow is unclear. The local velocities are around 10 m/sec, and the main characteristic of a microburst is a flow field that has a downburst core, that results in outflows that translate from vertical to horizontal due to the boundary conditions of the land or sea surface. That does frequently result in a toroidal vortex structure above the gust front, which has a counter flow rotation to the downburst/outflow vectors.

Still consider the THS is likely way out of trim, the B767 could be quite entertaining if trim was not used at lighter weights on using lots of thrust change, and is not unusual in that regard, merely notable.

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