[graham.d (OP)]

When flying back from Zurich to London City Airport on swissair LX456 yesterday (3rd December 2010), I observed the following:

Things I am sure of:

It was a little before noon (GMT) after a late take off because of aircraft de-icing, The Avro aircraft has a high wing and I was in a window seat a little forward of the starboard engine. Looking out (which I assume was north) there was a vapour(?) trail heading southwards. The trail was very dark (almost black) which seemed unusual as all the surrounding clouds were white. It was also very dense and did not extend back indefinately. I was trying to work out what it was when the pilot made a small course correction to the south and my view was then obscured by the engine.

Things I am not certain of because I am aware of the fallibility of observation:

The trail was some distance away (several miles) but was getting closer quickly. It was higher than our aicraft by a few thousand feet and I guess we were at around 30,000 feet. The dark vapour seemed to be very turbulent and thick encompassing whatever was causing it.

So what was it? I have never seen any aircraft produce such an effect. I did wonder whether it could have bee a meteorite burning up but there was no fireball that I could see. Any ideas?

[Geezer]

S. Claus testing out his new sled perhaps, or he may have been picking up a few items from the Gnomes.

[RD]

... there was a vapour(?) trail heading southwards.
The trail was very dark (almost black) which seemed unusual as all the surrounding clouds were white.

Possibly the shadow of an aircraft's vapour trail cast on a cloud ... http://www.thenakedscientists.com/forum/index.php?topic=26134.0

[graham.d (OP)]

Definitely not a shadow; there were no clouds immediately near this trail in any case. The vapour was more like smoke - very dark and thick.

There were no fat blokes in red or reindeer either :-)

[JimBob]

It could have been a jet that was having a flame-out in one of its engines. Jet fuel is similar to kerosene and burns very dark when not fully combusted. Ever had a kerosene lamp?

[graham.d (OP)]

Thanks JimBob. That sounds plausible.

[RD]

S. Claus testing out his new sled perhaps, or he may have been picking up a few items from the Gnomes.

Can't be: he's got the sack for using blue material ...
  http://news.sky.com/skynews/Home/World-News/Bad-Santa-Father-Christmas-Fired