Ice is the most dangerous natural element affecting the security of commercial carriers. As soon as the presence of ice is detected, adapted flight procedures - switch on deicing system, increasing engine power, exit auto-pilot mode, etc. - must be promptly performed.

Therefore, it is critical that the crew's decision-making process be supported by easily available and reliable information about ice build-up.

If ice detection is performed on the latest aircraft generation by using Electronics Sensors, authorities require that Visual Icing Indicator (Ice Cue) be installed. As a result of recent accidents, this recommendation has been restated by FAA.
It is to be noted that such indicators - propeller cone, windshield wipers, wings edge, thin metal plate - are often not lighted and cannot be used at night without an external dedicated spotlight and are positioned behind and far from the cockpit.
These devices do conform to authorities recommendations, but they are troublesome and creates unnecessary workload to the crew, especially during critical flight phases such as landing. More importantly, their legibility is often not reliable.