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Why are there holes in aircraft windows?

Four “interesting facts about flying” include the cheapest day to travel and why there’s a tiny hole in planes’ inner windows.

The Finnish airport operator Finavia has listed four “interesting facts about flying”, illuminating what regular travellers may have wondered at times.

Answering the first question, why is there a tiny hole in the aircraft’s inner window, Finavia says that it “plays an important role in allowing the aircraft window to breathe – to lower and balance the air pressure between the glasses”.

Aircraft windows are usually made of three acrylic panels. The outermost window maintains the air pressure. If that is damaged during the trip, the middle window acts as a spare window.

In the event of an emergency, the hole helps to keep the middle window intact until the aircraft lands. The hole also releases moisture and prevents windows from freezing and fogging up.

Drawing attention to a second point, that morning flights have less delays, Finavia explains that there are dozens of flights per day that use the same aircraft, so a morning delay can mean that flights leave late in the afternoon and evening. Even a delay of five minutes will shift the flight time for a plane’s next flight.

Dry air
Thirdly, addressing the fact that the air in the cabin is “considerably drier than most places on land”, on average below 20%, whereas the humidity in the world’s deserts is around 50%, Finavia advises, “Remember to drink water when flying!”

Finally, the airport operator says that Fridays and Wednesdays are the cheapest days to travel, at least from Finland to Europe. The most expensive travel date is usually Saturday, it adds.

Outside Europe, Wednesdays are “a good bet for cheap flights”, while for long-haul flights the most expensive travel date also tends to be Saturday.

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