After 9/11, the Fed both lowered the Fed Funds Rate and injected a big shot of liquidity into the banking system. This was done without any attention to banking stats, economic indications, etc. This was also done prior to the stock/bond markets re-opening after 9/11. Total amount (these are from memory, so please forgive me if I'm in error) was about $188+ billion injected over 9/12, 9/13 and 9/14.

Back then, remember, there were billions of dollars in personal, commercial and inter-bank checks that were waiting to be cleared sitting in planes that were grounded. Banks' books were going to be out of balance for at least a week after checks started to clear again, so the Fed stepped in and made sure there was enough liquidity for banks to continue operating until all the checks trapped in the air transport system could be cleared and returned.

Most people don't give a second thought at to what happens when they write a check. Before "Check 21" became instituted (arising out of 9/11), checks were collected by the banks that accepted them, then taken by courier to larger banks and check-clearing centers around the country. For example, all the casinos and banks in Reno used to pile all their checks into courier bags and take them down to the airport at Reno, where they would go onto one of two flights six nights a week in a Piper Cheyenne down to Las Vegas, where the checks would be processed and cleared. The planes would pick up checks processed the day before in Vegas and return them to banks in Reno on their return run. I learned of this while taking flight training in Reno, because it was a plum job for someone who had a CFI/IFR/multi rating to build hours towards an ATP license. The pilot doing the check run was paid almost nothing, but the company paid for the fuel and everything else, so you could build the required flight time on a two-engine complex aircraft.

When the air system was unlocked and planes could start flying again, the Fed withdrew the excess liquidity in the system. 

Coming out of this, "Check 21" was created to avoid another such shut-down of the banking system.

http://www.federalreserve.gov/paymentsystems/truncation/