Why is "mayday" a distress signal?

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Why: In The Handmaid's Tale, Luke says that "mayday" comes from the French word "m'aidez."

Answer: It actually comes from the French venez m'aider, which means "come help me." The Mayday callsign was originated in 1923 by a radio officer at Croydon Airport in London. He was asked to think of a word that would indicate distress and would easily be understood by all pilots and ground staff in an emergency. Since much of the traffic at the time was between Croydon and Le Bourget Airport in Paris, he proposed the word "Mayday" from the French m’aider.
The recommended distress call format suggests the word MAYDAY said 3 times, followed by the vessel name or call sign 3 times. In the U.S., making a hoax Mayday call in the U.S. is a federal crime carrying sanctions of up to six years imprisonment, and a fine of $250,000.

Source: Wikipedia

The More You Know: Natasha Richardson starred in the film version of "The Handmaid's Tale" in 1990 with Faye Dunaway, Robert Duvall, and Aidan Quinn.