How about a real close up of the phenomenon. Note how close the contrails are, just behind the engines. Compare with the pic with the Turkish airliner below.

Here a nice effect in the sky where the shadow of a contrail is shown in the cloudy layer below. The mid day sun is right above slightly to the left giving this interesting sight.

In order for this cloud to appear the humidity, temperature and pressure must be just right. These conditions can only be met at high altitude. This picture shows a jet without a contrail behind, whereas at higher altitude another jet has left its trail. This means that the altitude for aviaticus to form on this particular day, was inbetween these two aircraft.

Aviaticus clouds normally dissipate within a quite short period of time. If the right atmospheric conditions are met, however, they can remain in the sky for a long time and, furthermore, grow in size extending horizontally.

On this particular day, during high pressure weather conditions, these aviaticus clouds were formed but didn't dissipate. With time they grew and together they almost turned a blue sky into overcast conditions.

In fact, some environmental groups have raised concern with a theory that this man-made cloud formation could increase the green house effect by increased cloudiness.

Just before sunrise with pinkish colours in the sky, a jet is flying below.

Just as the sun is setting, the passengers in this jet are enjoying the view.

A beautiful example of the atmospheric red shift at sunset with the contrail of a passing jet.

A close up of a Turkish Airlines Airbus A340 flying at 36000 feet, showing how close the cloud formation is to the aircraft's engines. This is, however, depending on the surrounding conditions.

Again, over the North Atlantic going west, a Lufthansa Boeing 747 leaves its trailing aviaticus in the sky.