Aegean Sea UFO
This strange, dark tail or plume above the Aegean Sea was filmed by Kerry Forides, a passenger on a flight to Greece.
The object initially arced upwards and then appeared to take a more horizontal flight path. The plume then seemed to dissipate.
The video sparked excited conversation and disagreement on the web, with people on YouTube and Reddit debating over the source of the plume, its trajectory, and possible earthly explanations.
A number of people suggested that it's simply an older jet such as a GE J-79 or F-4 Phantom II, both of which had turbo annular combustors. These types of flame tubes were notorious for producing black smoke, the result of unburned (and inefficient) combustion. This smoke was not welcome, as it left a prominent dark plume and resulted in visibility from great distances.