ATR Wingtip Vortex Phenomenon
Last week, on the way across the LTMA a Blue Islands ATR42 passed overhead at FL170. We were in a thin layer a few thousand feet below, ISA+7.
It was interesting to see a thin but clear wintip vortex extending aft from each wingtip for about three wingspan lengths. The AC was straight and level. Is this a usual phenomenon on ATRs? I've only noticed it before on aircraft manoeuvering agressively (high AoA) and flaps/wingtips of aircraft on approach (high AoA) in humid conditions, never at cruising speeds.