Aviation consultant Ken Pasker on Monday said that's dangerous because the routes aren't charted and other pilots don't expect helicopters to be descending through the corridor.
The FAA last year barred local air traffic between 1,000 feet and 1,300 feet above the river. The new rule was meant to keep sightseeing helicopters out of the path of other small aircraft passing through New York City.
But FAA managers later signed an agreement allowing helicopters from five companies to fly above 1,300 feet and descend through the corridor near Manhattan's 79th Street.
Concern over helicopter flights flared last week after an East River crash killed a passenger.