I have a HP Officejet Pro 8500 A909a connected to a Time capsule. My iPad 2 don't recognise the printer. Why?

AirPrint will only work if the printer is connected to the network not the USB port of the Time Capsule.

Read this: http://support.apple.com/kb/ht4356

The pad will print to any airprint compatible printer. Hp makes several, but i do not see yous on the list.

Here is the list

http://support.apple.com/kb/HT4356

You can download the hp eprint app from the app store and see if that works for you.

The 909 Series OfficeJets are not AirPrint compatible. You need to upgrade to a 910 model, or get an app to use your current printer.