Prior to approving the Foreign Air Carrier Permit, ET
service to the US was based on what is known as an "Exemption" which had to be renewed every year. That was because there was no USA-Ethiopia air services agreement in effect when ET
first applied to operate to the US in 1998, but the service was approved anyway under Exemption Authority.
When an air services agreement (open skies) was signed 3 years ago, ET
applied for a Foreign Air Carrier Permit to replace the previous Exemption authority and avoid all the red tape of annual renewals etc. Not sure why it took so long to finally approve the final Permit since the open skies agreement was signed exactly 3 years ago, May 17, 2005.
You'll find all the related documents in the US DOT docket website. Docket numbers 3727 and 4345.