Aeronautical Terms beginning with I

Ice Crystals

Ice crystals, which are often in high concentrations near convective weather systems and lower concentrations in stratus or cirrus clouds, can accrete within turbine engines and cause power loss when in high concentrations. Ice crystals are not typically detected by either conventional ice detectors or airborne radar, and typically do not accrete on external airframe surfaces.

Icing Envelopes

Icing envelopes used for the certification of aircraft for flight in icing conditions specify atmospheric icing conditions in terms of altitude, temperature, Liquid Water Content (LWC), and drop size represented by the Median Volume Diameter (MVD). The envelopes use the term mean effective diameter, but this equates to the MVD for the instrumentation and assumptions current at the time the envelopes were established.) There are two classes of icing envelopes: continuous maximum and intermittent maximum. The continuous maximum is for stratus-type clouds, and the intermittent maximum is for cumulus-type clouds.

Impingement

The striking and adherence of a water droplet on an aircraft surface. The impingement rate is the rate at which droplets of a given size collect on a particular surface. In general, impingement rates are higher for larger drops and smaller components, such as a very high frequency (VHF) or a Global Positioning System (GPS) antenna.