SÃO PAULO, Brazil - Officials struggled Thursday to determine why a jetliner raced down a runway before crashing in a fireball that killed at least 189 people — an accident that set off a fierce debate over whether to close Brazil's busiest airport. Security video released by the air force showed TAM Flight 3054 from Porto Alegre speeding down the tarmac more than four times as fast as other planes landing around the same time. The Airbus-320 skidded off the main runway in a heavy rain, jumped over a highway and slammed into a building Tuesday night, killing all 186...