How to restore an Spfile from autobackup older than 7 days

Whenever we issue in RMAN, RMAN> restore spfile from autobackup; then restoring from autobackup stops at seven days and then it arises message channel ORA_DISK_1: no autobackup in 7 days found. For example,

RMAN> restore spfile from autobackup;
Starting restore at 31-AUG-08
using channel ORA_DISK_1

channel ORA_DISK_1: looking for autobackup on day: 20080831
channel ORA_DISK_1: looking for autobackup on day: 20080830
channel ORA_DISK_1: looking for autobackup on day: 20080829
channel ORA_DISK_1: looking for autobackup on day: 20080828
channel ORA_DISK_1: looking for autobackup on day: 20080827
channel ORA_DISK_1: looking for autobackup on day: 20080826
channel ORA_DISK_1: looking for autobackup on day: 20080825
channel ORA_DISK_1: no autobackup in 7 days found
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 08/31/2008 01:31:12
RMAN-06172: no autobackup found or specified handle is not a valid copy or piece

Whenever you give RMAN to RESTORE SPFILE FROM AUTOBACKUP or RESTORE CONTROLFILE FROM AUTOBACKUP, RMAN begins the search on the current day or on the day specified with the SET UNTIL caluse. If no autobackup is found in the current or SET UNTIL day, RMAN checks the previous day. In this way RMAN by default checks for 7 days autobackup from the current or SET UNTIL day.

However if you want to extend your searching of autobackup more than 7 then you have to use MAXDAYS option with the RESTORE command.

For example,
RMAN>restore spfile from autobackup maxdays 30;
or
RMAN>restore controlfile from autobackup maxdays 30;

In these cases autobackup searches will be performed up to 30 days from the current or SET UNTIL day.