Does this do what you want?
[VBA]Sub copy_rows()
Dim sA As Worksheet, sB As Worksheet, rCopy As Range
Set sA = Sheets("Flap-A")
Set sB = Sheets("Flap-B")

If sB.Range("A3") = "" Then
Exit Sub
Else
If sA.Range("A2") <> "" Then
Range(sB.Range("a3"), sB.Range("a3").End(xlToRight).End(xlDown)).Copy _
sA.Range("A" & Rows.Count).End(xlUp).Offset(1)
Else
Range(sB.Range("a2"), sB.Range("a3").End(xlToRight).End(xlDown)).Copy _
sA.Range("A" & Rows.Count).End(xlUp).Offset(1)
End If

End If
End Sub[/VBA]