For example if you look at V 23-165-597, from Seal Beach CA to Ocean Side CA, you will notice that it goes through restricted area for Camp Pendleton (R-2503A & D):
I was trying to understand what is the rule as far as ATC Clearance to enter those Airspace or any other Airspace in general when you are on those Victor Airways.
Where can I find the FAA rules about these Victor Airways?
Short answer: yes, with permission. Whether or not you're on an airway isn't really relevant.
The basic regulations on restricted airspace are in 14 CFR 91.133 and they apply to all aircraft on all flights:
(a) No person may operate an aircraft within a restricted area (designated in part 73) contrary to the restrictions imposed, or within a prohibited area, unless that person has the permission of the using or controlling agency, as appropriate
The AIM 3-4-3 also makes it clear that you can enter restricted airspace (my emphasis):
Restricted areas contain airspace identified by an area on the surface of the earth within which the flight of aircraft, while not wholly prohibited, is subject to restrictions.
And it has details of how ATC handles IFR traffic:
1. If the restricted area is not active and has been released to the controlling agency (FAA), the ATC facility will allow the aircraft to operate in the restricted airspace without issuing specific clearance for it to do so.
2. If the restricted area is active and has not been released to the controlling agency (FAA), the ATC facility will issue a clearance which will ensure the aircraft avoids the restricted airspace unless it is on an approved altitude reservation mission or has obtained its own permission to operate in the airspace and so informs the controlling facility.
In other words, you can fly through restricted airspace if the controlling agency gives you permission, either directly or via ATC. In the specific case of the Camp Pendleton restricted areas, the Los Angeles sectional says that you should contact LA Center or SoCal TRACON (for R-2503D), and shows that the areas are not active 24 hours per day:
So in theory you can fly through at 3am without asking anyone, but if you're planning a flight that goes through a restricted area you should make sure you get a flight briefing and ask the briefer about that point specifically. And it wouldn't hurt to confirm again in the air before entering, in case the areas 'go hot' suddenly.
Camp Pendleton's current R-2503D zone, which extends along the California coastline to the southeast of the former Camp Pendleton MOA, is a special case.
First off, it can only be activated via NOTAM for a maximum of 20 days a year from 0600 to 2359, and a maximum of 90 days a year between 2400 and 0600 local time. So, for 345 days a year, you can fly right through this airspace at 2000AGL or higher, either VFR or IFR under guidance from LA Center. MCB Pendleton's airstrip remains Class D, and the majority of the remaining R-2503 airspace (including R-2503A below 2000 feet) is active 7 days a week from 0600-2359 local time, extensible by NOTAM.
Second, when R-2503D is active, non-participating craft may still gain entry by contacting MCB Pendleton's tower, codename "Longrifle", whose frequency has been released for general aviation. Clearance would be granted case-by-case based on the nature of activities within the airspace at the time; if denied, the detour for all routes through R-2503D is just offshore, within glide distance of land in most cases.
