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Old 30th Aug 2009, 05:16
  #5 (permalink)  
Join Date: Apr 2000
Location: South of YSSY
Age: 68
Posts: 437
I have observed a similar phenomenon a few times whilst paxing in 737s with the winglets; a visual "discontinuity" about one third up the leading-edge of the winglet at cruising altitude. On descent it moves away (can't recall which direction) and becomes invisible.

I assumed this to be a change in refractive index of the air due to shock-wave/compressibility issues, and after we landed I mentioned it to the aircrew as I disembarked via the for'ard door. Although they hadn't actually seen it themselves they said they'd try to observe it next time they deadheaded in a company aircraft.

Nice to see you actually managed to photograph it. It seems the phenomenon is only visible under certain conditions of sun's angle relative to the aircraft, plus speed and altitude etc.
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