9/11 and the ability of the US Air Force

I had one a few questions:

Why USAF in November 9, do not use the AWACS, to detect 2 planes hijacked left after 2 planes crashing into the Twin Towers, the US Aviation Authority has asked all the flights landing to the nearest

Why are not there any SAM systems around the Pentagon

Why OTH radar systems, long-range radar can detect the United States ballistic missile threats and other hostile military, can not detect the remaining aircraft in the sky after the Department of Aviation issue the command landing immediately

Has 4 flights operated by two F-15 and two F-16s took off to find 2 flight United 93 and AA77, however, why the both of radar (F-15/16) undetectable the 2 planes that, although Boeing has huge RCS