Component:

<aura:component implements="flexipage:availableForRecordHome,force:hasRecordId" access="global" >
    <aura:attribute name="record" type="Object" description="The record object" />
    <aura:attribute name="recordError" type="String" description="An error message bound to force:recordData" />
    <lightning:card>
        <force:recordData aura:id="recordLoader"
                          recordId="{!v.recordId}"
                          fields="Subject, Description"
                          targetFields="{!v.record}"
                          targetError="{!v.recordError}"
                          recordUpdated="{!c.handleRecordUpdated}"
                          mode="VIEW"/>
        Case Id: {!v.recordId}<br/>
        Case Subject: {!v.record.Subject}
    </lightning:card>
</aura:component>

JavaScript:

({
    handleRecordUpdated : function(component, event, helper) {
        var eventParams = event.getParams();
        if(eventParams.changeType === "LOADED") {
            console.log( 'Record Loaded' );
            var flow = component.find("flowData");
        } else if(eventParams.changeType === "CHANGED") {
            console.log( 'Record Changed' );
        } else if(eventParams.changeType === "REMOVED") {
            console.log( 'Record Removed' );
        } else if(eventParams.changeType === "ERROR") {
            console.log("Error Change Type");
        }
    }
})

Output:

Note:

force:recordData loads the record asynchronously by pulling the data from the Salesforce Server. So, recordUpdated should be used to monitor when the record is Loaded, Changed(Updated), Removed(Delete) and errored out.