Why do modern airliners have windscreens which open? [duplicate]

Question

I'm sure it must be nice for pilots on a hot day to pop open their windscreen while waiting on the tarmac, but is there a good engineering or safety need for them? There must be a significant amount of cost and time effort in making a windscreen both openable and safe. If the pilots really need some fresh air, they're usually pretty close to the passenger door.

I can imagine there were valid historic reasons for having them: when planes were smaller and instrumentation not so sophisticated, you might literally want to take a proper look at your propellers spinning before setting out. But why do we persist with them?

737 Max with both its cockpit windows open source

Airbus A380 with open window source

Answer 1

Not all modern aircraft have windows that can be opened. The Boeing 747 for example does not.

On the Boeing 737, the windows can be opened for two reasons:

• Emergency Evacuation: When the aircraft needs to be evacuated, there is always a way to escape from the flight deck without going through the cabin. On the Boeing 737, this is accomplished through the windows. From the 737 NG FCOMv2 (1.40.30):

  The flight deck number two windows can be opened on the ground or in flight and can be used for emergency evacuation. To open the window, depress the trigger and turn the handle back and inboard. After the window moves inboard, move it back until it locks in the open position.

  [...]

  Flight Deck Window Emergency Egress

  If the flight deck number two windows must be used for emergency egress, use the following procedure:

  • open the window
  • open the escape strap compartment (above and aft of window)
  • pull on the escape strap to ensure it is securely attached
  • throw the strap out the window
  • sit on the window sill with upper body outside
  • exit in accordance with the following illustration.

  CAUTION: Ensure the escape strap is securely fastened to the airplane.

  Aircraft without windows that can be opened, have an escape hatch in the ceiling. You can see the 747 escape hatch in the following image from the FCOM:

  

• Smoke or Fumes Removal: If there is a fire in or near the cockpit that cannot be easily extinguished (e.g. fire in the electronics behind the screens), the smoke has to be removed in order to continue to fly the aircraft. This can be accomplished by opening a window. From the 737 NG QRH (8.19):

  Smoke or fumes source is confirmed to be on the flight deck:

  Caution! Window should not be opened unless the source is confirmed to be on the flight deck.

  Establish normal holding speed. High airspeed may prevent opening the window.

  Open the first officer’s sliding window.

  On aircraft where the windows cannot be opened, there is a dedicated system to evacuate the smoke, e.g. from the Boeing 747-400 QRH (8.43):

  Smoke or fumes persists or is severe and the smoke or fumes source is determined to be on the flight deck:

  Pull the smoke evacuation handle. Pulling the smoke evacuation handle when smoke or fumes source is not on the flight deck may bring the smoke or fumes into the flight deck.