"which plans" is correct and usable in written English.
You can use it to ask or refer to a specific plan. For example, "What are the details of the plan which plans to expand the business?".
See how many planned items got done, what problems are you facing and which plans are still unfinished.
Or Britain, which plans to replace six benefits with one.
But the tobacco industry, which plans to appeal, appeared unfazed.
It is impossible to predict which plans, however.
Spain, which plans a bond sale on Thursday, could be subjected to similar investor wariness.
Writer attended a lunch at the Time & Life Building, at which plans were unfolded.
The company is owned by Dollar, which plans a 1200-branch network.
To turn on Boehner: The Tea Party Nation, which plans to back a challenger in 2012.
Perfectly legal, says Polpharma, Poland's biggest drug company, which plans to produce it.
Who would make the decisions about which plans people could buy?
The Authority, which plans to have programs operating before summer, said that many tenants were exempt.
