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I I I I I I I I I I I I I I I I I I I VHF receiver was used by the radar meteorologist to monitOlt" the pilot's transmissions to the ATe facility. By timing his trans- missions with the monitored ATe - pilot conversations, the meteorologist was able to keep interruptions to a minimum. 2.6 Project Aircraft A turbo-charged Piper Navajo was used as the project aircraft. The airplane was fully equipped for extended flights in IFR weather. Normal climb out to seeding altitude (16,000-20,000 ft) required 20-25 minutes. Table II gives the detailed charader- istics of the aircraft. Figure 5 shows the project airplane, N9094Y. 2.7 Seeding Material and Delivery System Seeding was done with droppable pyrotechnic flares. Each flare consisted of two main parts; a stationary cartridge and an ejectable plug. The plug was made of combustible material blended with a silver iodide - ammonium iodate complex. An electrical impulse simultaneously ignited and ejected the plug which fell for about 45 seconds (5,000 ft). Each burning plug generates 20 grams (7/10 of an ounce) of active silver iodide (AgI). The emitted smoke contains large numbers of small AgI particles which act as ice nuclei. Figure 6 gives the ice nuclei effectiveness of the AgI pyrotechnic. All of the ejected portion of the flare vaporized during its free-fall. The curtains of AgI smoke, created by the falling flares, are quickly mixed throughout the cloud updraft creating a rapid onset of ice crystal formation. As described in Section 3, certain days were ran- domly selected as "control" days. On these days a placebo was used. The placebo ("dummy") flares contained only fine sand which has a negligible ice nucleation efficiency. 15 - '.