How to loop on table of objects(TYPE TABLE OF REF TO) with WHERE condition

Hi,

I need to loop with a where clause on table of object. But I not able to find out the correct syntax for where condition.

Sample Code:

Data: t_flight   type table of ref to lcl_flight,

         Rf_flight type ref to            lcl_flight.

Loop at t_flight into rf_flight where.

How to refer to the class attribute in where condition.

Please help.