What technologies would you use to find the black box from Air France flight 447.

The original debris was found roughly 400 miles (640 kilometers) northeast of the Fernando de Noronha islands off Brazil's northern coast, an area where the ocean floor drops as low as 22,950 feet (7,000 meters) below sea level. The sturdy black boxes — voice and data recorders — are built to give off signals for at least 30 days. This is a vary remote mountainous area.