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"Temperature 33°, wind from 280°, velocity 42 miles per hour."
At 4:06, the Chicago Airway Traffic Control cleared Trip 21 from the Cleveland boundary to cross the McCool fan marker (about 35 miles southeast of the Chicago Municipal Airport) at 6000 feet or 500 feet on top, whichever was the lower. At 4:07, the Chicago station of United questioned Captain Scott as to whether he wished to cross McCool fan marker at 4000 feet or 500 feet on top. Upon Captain Scott's reporting his election to stay on top, the station transmitted a message as follows:
"OK. They have reported light ice lower part of the overcast. Will advise Airways and get your clearance."
Captain Scott then elected to fly on top of the overcast, reporting as follows:
"United 21 OK. Will cross on top no matter what."
At 4:21 a change is clearance was requested and obtained from the Chicago Airway Traffic Control for Trip 21 to fly 500 feet on top, crossing McCool at 5500 feet. At 4:34 Trip 21 reported over Goshen 500 feet on top of the overcast, reporting on outside temperature of 33 degrees at this altitude. At 4:54 Chicago Airway Traffic Control advised the United dispatcher to instruct Trip 21 to hold at Lansing (about 20 miles southeast of the Chicago Municipal Airport) at 6000 feet and to expect an approach clearance at 5:25. At the time this was transmitted by the United dispatcher at 4:57, Captain Scott requested and was given the 4:35 weather observation at Chicago. This reported that the ceiling was 1000 feet with lower scattered clouds at 600 feet, the visibility was
