Verizon is acknowledging widespread failures in its 911 emergency backup systems during a June storm that hit the Washington region.
The report and Verizon officials say they did not know the system was out in Fairfax County until the county alerted them. It also admits problems with Arlington County's 911 system that the company had previously denied.
The report also says drained batteries, faulty generators and a failure of staff to fully explore the problem contributed to delays in restoring full 911 service.
A Verizon official says the company also erred in treating the problem as a service complaint rather than a large-scale outage.
Verizon is now auditing backup power systems throughout the Washington region.
The report is scheduled to be presented Wednesday to the Metropolitan Washington Council of Governments.