In the software used in a call routing center in Englewood, Colorado, there was a programming error in a single piece of software. Sounds minor, but this error could have had horrible implications: it knocked out 911 service to 11 million people in Washington state, North Carolina, South Carolina, Pennsylvania, California, Minnesota, and Florida for six hours in April. More than 5,600 calls in affected areas didn’t go through. How did this happen, and can we prevent it from happening again?

The outage started around midnight Pacific time. Calls routed through the Public Safety Answering Point (PSAP) in Colorado that couldn’t be routed were supposed to go through a PSAP in Miami instead, but a coding error meant that the system in Colorado had no idea that there was a problem. Instead of going to Miami, thousands of call went nowhere.

If you’re interested in the technical reasons for the outage, you can read up about it in the FCC’s full report, but the reasons for the outage are problems with the phone system as a whole. We really have two different 911 systems operating right now: the legacy systems that have run phone and emergency services for years tended to be located near their customers, not across the country. Now that telecoms are switching to an Internet Protocol-based phone system, emergency systems are switching as well.

April 2014 Multistate 911 Outage: Cause and Impact [FCC]
A preventable coding error knocked out 911 service for millions [The Verge]

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