Fuselage, Wings and Stabilizing Surfaces — Page 19, Lesson 25

Let's pick up with the fuselage and its openings — the windows and doors. I want to walk you through the Eye Reference Position first, because it's a small but important concept for the flight deck. At each pilot station, fixed markers or other guides are installed. These let the pilots position themselves in their seats for the optimum combination of outside visibility and instrument scan. That's the Eye Reference Position — it standardizes the visual attitude, especially on approach and landing. So when you sit down, you adjust your seat until your eyes line up with that marker, and you know your view of the runway and your instruments is exactly as the designers intended. Now, the Direct Vision window — often called the DV window. This is an opening window in the control cabin. Its purpose is to let the pilot land the aircraft safely should forward vision be restricted. Think of it as your backup view if the main windscreen is obscured. The DV window slides open on a track that first lets the aft end of the window tilt in, then it slides along the track until it's opened. So it's a two-step motion — tilt in, then slide back. The DV window has three specific uses I want you to note. First, it can be used in the event of a failure of the demisting system. Second, it can be opened in flight if the aircraft is depressurized. And third, depending on its size, it may also be used as an emergency exit. On light aircraft, the flight compartment windows are generally perspex — that's the acrylic material. Now let's move to the passenger cabin windows. These are designed to be 'fail-safe'. They normally have two panes of acrylic plastic mounted in an airtight rubber seal, fitted into a metal window frame. Here's the key point: the inner and outer panes are each capable of taking the full cabin pressurization load. So if one pane fails, the other will prevent loss of cabin pressure. That's the fail-safe principle — redundancy in the pressure boundary. Finally, aircraft doors. Doors may be side or top opening. All passenger doors on pressurized aircraft are now of the plug type. Let me explain what that means. When closed, the internal pressure holds the door shut, and locking pins engage with the frame structure to ensure it cannot open in flight. To open a plug type door, it is pulled inwards and rotated sideways. Some open outwards for better access. The plug door has to meet several requirements. It must be able to withstand the pressure loads if the aircraft is pressurized. It has to have a means of preventing the aircraft being pressurized with the door unlocked — that's a safety interlock. It must be easy to open in an emergency, and usually has escape slides built into the construction of the door. A visual inspection panel is also required. Unpressurized aircraft have doors of a lighter construction, since they don't face those pressure loads. And one more type — freight doors. Some aircraft have freight doors in the side of the fuselage. These usually hinge upwards and open by means of an electric motor or hydraulic power pack. The loads go through the hinges. So the hinge structure carries the weight of the door and the freight handling forces. Let me show you the window and door arrangements on the aircraft so you can see how these fit together. That's the fuselage openings — the Eye Reference Position for your seating, the DV window for restricted visibility, the fail-safe passenger windows, and the plug-type doors with their safety features.