I recently rode in the jumpseat of an A330 during a flight. Quickly after touchdown, the PF selected idle reverse, and no further. As soon as he did so, I could hear the engines begin to spool up, and saw the EPR indications rise, before the engines went back to idle reverse about 3 seconds later. My question is, do the engines automatically begin to spool up as soon as idle reverse is selected in order to more rapidly provide maximum reverse thrust if that setting is subsequently selected?
If so, this is unusual, as all other engines will remain in idle until further reverse thrust is selected. I looked in the FCOM and FCTM, and asked the pilot flying himself, but could get no answer. The engines were Rolls-Royce Trent 700s.