Aeros laws in the USA

[cambioso]

Here's one for the US FAA gurus........
Here is the extract from FARs about aerobatic flight in the USA.

§ 91.303 Aerobatic flight.
No person may operate an aircraft in aerobatic flight -

(a) Over any congested area of a city, town, or settlement;

(b) Over an open air assembly of persons;

(c) Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport;

(d) Within 4 nautical miles of the center line of any Federal airway;

(e) Below an altitude of 1,500 feet above the surface; or

(f) When flight visibility is less than 3 statute miles.

Item (d) (Within 4 nautical miles of the center line of any Federal airway) is the query.
Is it permitted to carry out aerobatics beneath and clear of the base of an airway in the USA? The "within 4 miles of the centre line" implies that even if you are in the "free airspace" underneath the airway, you may not carry out aeros because you are within 4 miles of the centreline (although you are not inside the airway).....
In the UK, provided that you remain clear of the airway, you are perfectly at liberty to perform aeros beneath.
I would appreciate a definitive answer from a Qualified Guru (please no "I believe", or "I am fairly sure" etc!!).
Many thanks,
Jez.

[Mark 1]

There is a degree of ambiguity; 14 CFR 1.1 doesn't define 'federal airway'. FAA order 7400.9Z does define victor routes etc to be federal airways extending to the base of Class E unless otherwise defined.

So my inference is you effectively have to project 4NM from centre line down to ground level (or 1200' anyway which amounts to the same).

I live near quite a criss-cross of victor routes so stick to an area which meets all those restrictions

[n5296s]

+1 for Mark 1 - unlike in the UK, US airways don't have a base (well, I suppose it's the limit of Class E but unless you want to fly somewhere in the middle of Colorado that amounts to the same thing).

And as he says, round here (Bay Area) it's tricky to find anywhere big enough to be useful that fits this definition.