GPS. Flight Management Systems. Simulators.
Actually, the two WTC hijackers nearly collided over the water while on the "final approach" to the Twin Towers. They weren't THAT good.
It further throws into doubt their ability to master the intricacies of the instrument flight rules (IFR) in the 45 minutes from take off to the point of impact.
They weren't "in the system," i.e., flying according to IFR. The day was VMC (visual meteorological conditions), or severe clear. Just because commercial airlines are required to fly under IFR doesn't mean that a hijacker of a commercial airline is gonna follow the rules! Sheesh.
A further question raised by the inquiry was why none of the pilots concerned had alerted ground control. It stated that all pilots are trained to punch a four-digit code into the flight control’s transponder to warn ground control crews of a hijacking - but this did not happen.
Because they were dead.
And for good measure, I'm sure the hijackers either popped the circuit breakers for the transponder or just turned it off.