natural icing flights and additional simulated icing tests were accomplished with a uh-1h helicopter equipped with an advanced ice protection system. this testing was the third icing test program accomplished with the test aircraft, but the first to include natural icing conditions. the simulated icing tests were conducted in the national research council (nrc) spray rig at ottawa, canada. the natural icing flights were made from the ottawa international airport. seven tests in the spray rig and ten natural icing flights were made totaling 30.4 flight hours of icing testing. icing was encountered on five of the natural icing flights. the icing conditions ranged from 9.15 gram per cubic meter liquid water content at -18 c to 0.30 grams per cubic meter at -2 c. the aircraft operated in icing conditions on each of the flights from 40 minutes to a little over one hour. the number of main blade deicing cycles required under the conditions experienced varied from three to five