Aircraft Icing

Ice formation on aircraft can disrupt the smooth flow of air over the wings and prevent the aircraft from taking off or decrease the pilot's ability to maintain control of the aircraft. Despite a variety of technologies designed to prevent ice from forming on planes, as well as persistent efforts by the FAA to mitigate icing risks, icing remains a serious concern. This statement provides info. on: (1) the extent to which large commercial airplanes have experienced accidents and incidents related to icing and contaminated runways; (2) the efforts of FAA to improve safety in icing and winter weather operating conditions; and (3) the challenges that continue to affect aviation safety in icing and winter weather operating conditions. Charts and tables.

A series of passes on 6 December 1979 through multilayered-supercooled stratiform and stratocumulus clouds by the Air Force Geophysics Laboratory's instrumented C-130E cloud physics research aircraft is used to evaluate a Rosemount Ice Detector. The response of the detector to icing conditions is compared with measurements from a J-W liquid water content meter and the Knollenberg Axial Scattering Spectrometer Probe (ASSP). A procedure to adjust for zero drift of the J-W instrument is developed. Comparison of liquid water measurements from the J-W and from the ASSP indicate that these data are highly correlated and similar in magnitude. A procedure for extracting useful information from the Rosemount Ice detector has been developed. The icing conditions in the cloud systems studied are typical of the range of conditions in winter stratiform clouds. Liquid water (LWC) values of 0.3 g/cu m and median volume diameters of 15 micrometers were most frequently observed. The results of the analysis show that the Rosemount Ice Detector is a sensitive indicator of the fluctuations of liquid water in clouds with LWC not exceeding 0.8 g/cu m -3.

Data on the meteorological parameters pertinent to the aircraft icing problem are so summarized as to give the frequency of occurrence of observed icing situations according to two of the parameters. The summarized data indicate that statistical relations exist between some of the parameters. A method, based upon the collection efficiency of an airfoil and the frequency occurrence of icing situations with various liquid-water contents and mean-effective droplet sizes, is proposed for the selection of design criterions for ice-protection equipment. The method provides a convenient means of calculating the percenteage of icing encounters in which the water collection exceeds the design rate.

Title of supplementary volume: De/anti-icing optimization.

Required reading for every pilot, this resource identifies different icing types -- including new phenomena such as supercolled drizzle droplets. Covers both ground and airborne icing for VFR and IFR pilots in high- and low-level operations.

Icing tests were conducted to document ice shapes formed on three different two-dimensional airfoils and to study the effects of the accreted ice on aerodynamic performance. The models tested were representative of airfoil designs in current use for each of the commercial transport, business jet, and general aviation categories of aircraft. The models were subjected to a range of icing conditions in an icing wind tunnel. The conditions were selected primarily from the Federal Aviation Administration's Federal Aviation Regulations 25 Appendix C atmospheric icing conditions. A few large droplet icing conditions were included. To verify the aerodynamic performance measurements, molds were made of selected ice shapes formed in the icing tunnel. Castings of the ice were made from the molds and placed on a model in a dry, low-turbulence wind tunnel where precision aerodynamic performance measurements were made. Documentation of all the ice shapes and the aerodynamic performance measurements made during the icing tunnel tests is included in this report. Results from the dry, low-turbulence wind tunnel tests are also presented.