“Three days before the full scale Chinese attack, MacArthur flew in an unarmed aircraft at 5,000 feet directly above the safe haven created by Truman, He flew from the mouth of the Yalu along the entire length of the front to the Siberian border.”
Yes, he did. And he said he saw no evidence at all of any Chinese buildup. The problem is, thousands had already crossed the Yalu into North Korea. Also, the CCF was heavy in manpower but very light on mechanized assets, so at 5,000 feet it’s pretty easy to miss troops who blended in quite nicely with the terrain, whereas rolling stock and mechanized assets would be easier to see.
Because tracks left by such movements would be quickly covered by snowstorms.