Why, when boarding and landing, ask to open the porthole shutters?
Despite the high manufacturability of modern aircraft, no one is insured against emergency situations, and most of them fall on the landing and take-off stages. In this case, the main task of the pilot is to take all measures to save passengers by committing an emergency landing. Such a landing is made on any suitable territory and may be sufficiently tough.
Therefore, during the landing and take-off, flight attendants need to be especially closely following what is happening by board in order to inform the pilots on an abnormal situation. And it is impossible to do it with closed curtains. Yes, and rescuers will easier figure out what is happening in the cabin if the porthcomes are open. This is the first reason why flight attendants are asked to open the porthole shutters.
Modern reality dictates the second reason: before opening the doors, the crew must be sure that the plane is not waiting for the plane. Consequently, the aircraft will be safe, and passengers. Passengers can also prompt about suspicious movements at the airport.
There is a more peaceful reason: the eyes should get used to natural light to be easier to navigate. In addition, the open porthole allows you to see how the plane sits. Consequently, soothes those who are afraid of flights.
It is afraid that, being open, the porthole will break in the case of a tight fit, not worth. It is designed so that it can withstand the pressure between the cabin and the external atmosphere, equal to the load of about 4 tons. (We previously told why the portholes make an oval form.) Present the situation in which the pressure will be even more, it is extremely difficult. But even if the depressurization occurs, the crew will immediately decrease to a safe height, and the oxygen is enough for another 15-20 minutes of flight. During this time, pilots need to have time to assess the situation and make an emergency landing. Open portholes can be useful here too.