Condensation trails (contrails) form when aircraft engine exhaust rapidly cools to form ice crystals.  Contrail formation is dependent upon the atmospheric temperature and humidity, aircraft engine type and thrust setting, and aircraft fluid dynamics. 

Pilot Alert System:  designed, manufactured, tested, certified and maintained by Ophir.

The Pilot Alert System (PAS) is a light detection and ranging (lidar) system designed for detection of contrail formations behind the B-2 Stealth Bomber. The PAS system features include

• sensitivity to aerosol backscatter coefficients better than 1x10^-5/ m sr 
• aerosol/soot density mapping from 0 to 300 meters
• 10 meter range resolution
• aerosol/soot profile computed once every second
• real-time indication of contrail/soot presence