So Google is now admitting to site speed and site uptime (or downtime) being a factor with rankings according to Google’s Webmaster Central Blog:
“Outages that are not clearly marked as such can negatively affect a site’s reputation. While we cannot guarantee any crawling, indexing or ranking, there are methods to deal with planned website downtime in a way that will generally not negatively affect your site’s visibility in the search results.”
The blog post includes recommendations about what HTTP result code is most appropriate to serve when your website is temporary down.
They say its better to return a 503 HTTP result code indicating the downtime is only temporary. Additionally you can use a Retry-After header to let Google know when to come back and crawl your site if you know how long the outage will last for.
The article doesn’t specifically say it will absolutely avoid a drop in rankings, but its a step in the right direction.
You can read the full blog post here: How to deal with planned site downtime
