1.   His radios were tuned to air traffic control frequencies, and they were eerily quiet.

2.   The American crew then suggested that he try to hail the plane on an air traffic control frequency, which he did.

3.   Air traffic communication frequencies are published in specialized manuals, although their unauthorized use is illegal.

4.   The pilot followed time-honored emergency procedures, he said, including broadcasting his intentions on the universal air distress frequency.