Brazilian Air Traffic Controllers Put On High Alert
Many flight instructors will warn you to be very careful
when setting your transponder. They will tell you to be especially
mindful to avoid squawking "7" in the first digit because if you
add another "7" or" 6" or "5", this sets off alarm bells, warning
whistles, and panic horns for the controller--
signalling emergency, lost communications, and hijacking,
respectively.