Uses of a DV window
In larger aircraft . the openable DV window [ Direct Vision ]
consists of a sandwich layer of heavy perspex , so that when
the rest of the aircraft is iced up or descending, clear vision is possible through that window.
Moisture formed between the sandwich layers , is removed by a vial of silica gel crystals.
The DV window is a lot more robust than on a PA28 , as the larger aircraft are pressurised.