Enhanced Vision Systems

Susceptibility to ice formation may be another concern. Most equipment available today comes with self-contained heaters. When the system is activated, power is delivered automatically to the electrical elements and the viewing window temperature is maintained at around 70 F. In fact on cool days the lens of the sensor may be warm to the touch. If the heaters fail and the aircraft is in an icing environment, infrared energy will be absorbed by the ice and the effectiveness of the system will be degraded. The indication within the flight deck will often be a progressively fading image on the display. In this case the flight crew should turn off the enhanced vision system and the sensor unit should be sent to an authorized repair station for analysis.

The material used to construct the thermal eye is also a concern. In most cases the sensor is sealed from the factory and may be filled with an inert gas such as nitrogen to eliminate moisture. In the event the case is opened the gas charge will be lost. Germanium is one of the common photo optical materials used in the construction of the sensor.

If the lens is ever broken, use extreme caution when handling broken Germanium pieces or dust. It is recommended to wear gloves and a mask during any cleanup operation. Although Germanium does possess excellent properties regarding infrared radiation detection it is also susceptible to damage when it is exposed to direct sunlight for prolonged periods. There is a sensor currently in use that is manufactured from barium strontium titanate and is immune to heat and sun damage.

An electrically actuated lens cover may be employed to provide protection to the eye when the system is not in use. A recommended practice is to not operate the system when the aircraft is parked and pointed directly at the sun, and with the system selected off the lens cover should automatically close to provide protection against damage. Technology is in place to provide ongoing calibration to a sensor that has been exposed to direct sunlight. In the event of uncorrectable damage the only solution is to return the unit to the manufacturer for repair and detailed calibration.

As this type of system does work based on variations of temperature there are factors that may impact the system’s image quality. Some of the variables include the size of the target, background temperature, visible moisture, and even relative humidity. If the video image appears clear on a cool morning and a bit washed out on a hot and humid summer afternoon, there may not be a malfunction with the system.

As was stated earlier thermal imaging systems most often are made up of a cockpit-mounted ON/OFF switch as well as a video monitor and elsewhere in the airframe is a power supply and the sensor. Repairs are for the most part limited to sending out Line Replaceable Units (LRU).

By the way, for those of you wondering, no animals were hurt or killed during the writing of this piece. And about the shot that rang out, there was no gun involved. Someone in the hangar made a mistake troubleshooting an engine fire extinguisher. Sorry for the adrenaline rush.