Dear Siddharth,
Many thanks for your help in this regard. Yes, using FITV_POWL_APPROVER works on its own within its framework. I am little disappointed though, as we have MSS POWL framework and expected to handle events from other POWL queries which it receives. But in travel expenses case this behaviour is different and works a wrapper in the application itself and handles only its own events.
In summary, MSS POWL design allows to plug in the travel POWL queries but doesn't cater the purpose using SAP standard configuration and customers should aware of this. The only mechanism to make this to work is through enhancing the feeder class and capture the relevant events.
Once again thanks a lot for your help in providing the exact location pointer where to capture the events.
Regards
SP