Contrails

[forthbridge]

Hey all

Just saw a twinjet at altitude pass overhead on about 330 degrees. For some reason, for about ten seconds it's contrail vanished (today seems to be short contrails, nothing stretching way back), then reapeared for a few seconds, 'puffed out' and then appeared normally again. Never seen this before: is it a normal happening?

[Garry Russell]

Not unusual

The layers of air are not uniform and what is happening is that it is flying a uniform level at about the point where the contrails are forming and in some areas that is a bit higher than the flight level so it goes off and then lower and it comes back in and perhaps even lower so the trail is a little longer then shorter then off etc.

So if you drew a graph the level where contrails form would be peaks and troughs with the aeroplane flying through the middle in a nice straight line.

It could be though that in your part of the world the weather dictates it might not be so common as in other parts.

[forthbridge]

Cheers Gary, makes sense

Must admit, so many A/C pass overhead, you get used to seeing the contrails and don't really look for anything odd. It just so happened I was sitting in the shed with the door open and the A/C was approaching directly in my line of sight so I had a good view! Funnily enough, as it went overhead (on chacking radar 24 it was a Canada flight), followed by an Icelandair, it prodiced what I'd say was 'loud' noise from the engines (by comparison to normal) so I suppose the air's doing some odd things up there at the moment, although it's clear as a bell!

[Garry Russell]

Sometimes the high overflight are barely audible sometime quite loud....all depends on conditions