>how could there have been silence when the crash occurred?
Because cell phones don't transmit sound. They have vocoders (look it up) that detect the sounds
of human voices, and convert those sounds into phonetic symbols and transmit those instead
(with adjustments for various voice parameters like pitch). If there are no human voices, the phone
transmits nothing. In 2001, vocoders were pretty basic, and pretty crappy, which is why there
was a battle between US CDMA services and European GSM services (which were clearly better
at the time).