Some airlines have their flight attendants ask you and your fellow passengers to raise your window shades during take-off and landing. This isn’t about waking passengers up at the end of a red-eye or having all the shades up or down for the next flight, it’s about safety.
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The crew asks you to open your window shade because it helps them see outside better if they have to evacuate the aeroplane, and since most accidents happen during take-off and landing, that’s the time it makes the most sense to have the shades up. Besides giving flight attendants visibility into conditions outside so they can guide passengers to safety, having the shades up when it’s bright out also makes sure passengers’ eyes are adjusted to daylight if they do need to get off the aircraft quickly. Raising window shades during take-off and landing isn’t the policy on every airline, but if you’re asked to do so, you know it’s for a good reason.
The Real Reason Flight Attendants Make Your Raise the Aeroplane Window Shade [Conde Nast Traveller]