Don't you still need to get actual permission though to fly as a hobbyist in Class B--not just simple notification for flying less than 5 miles away from an airport? That being said--it's (ironically) easier (and MUCH faster) to call the Tower than it is to use the portal for 107 authorizations.
Airspace Restrictions
See attached screenshot.
That's true.
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Airports
Recreational operators are required to give notice for flights within five miles of an airport to BOTH the airport operator and air traffic control tower, if the airport has a tower. However, recreational operations are not permitted in Class B airspace around most major airports without specific air traffic permission and coordination.
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