U.S. Department of Transportation
Federal Aviation Operations Specifications Administration
B032. En Route Limitations and Provisions  HQ Control: 07/09/99 HQ Revision: 01a
The certificate holder shall comply with the following IFR en route limitations and provisions when conducting any en route operation under these operations specifications. Unless otherwise authorized by these operations specifications, the certificate holder shall not conduct IFR operations outside controlled airspace.
a. 
When conducting Class I navigation, an aircraft's position shall be "reliably fixed" as necessary, to navigate to the degree of accuracy required for air traffic control.

b.
  When conducting Class I navigation, the airways used and the off-airway routing predicated on airways navigation facilities shall lie within the operational service volume of the facilities defining the airways or off-airway routing.

c. 
When conducting Class I navigation, the facilities which define an airway, or an off-airway routing predicated on airways navigation facilities, shall be used as the primary navigation reference unless navigation is conducted using an area navigation system which is certificated for use in IFR flight for the conduct of Class I navigation over the routes being flown and authorized in accordance with paragraph B034 of these operations specifications.

d.
  Except for operations over routes designated with an MEA GAP (or ICAO equivalent), all navigation conducted over routes which contain route segments outside the operational service volume of airways navigation facilities shall be conducted in accordance with Class II navigation requirements.  All Class II navigation predicated on airways navigation facilities shall be conducted only within those areas where the aircraft`s position can be "reliably fixed" (at least once each hour using these facilities) to the degree of accuracy required for air traffic control.