Yes it is administrative (regulation) vs. criminal law.
In this case the 0.04 limit rule comes from FAR Part 120.37(b):
(b) Alcohol concentration. No covered employee shall report for duty or remain on duty requiring the performance of safety-sensitive functions while having an alcohol concentration of 0.04 or greater. No certificate holder having actual knowledge that an employee has an alcohol concentration of 0.04 or greater shall permit the employee to perform or continue to perform safety-sensitive functions.
FAR 120.37 is enforced administratively by the FAA. Consequences of violating this regulation may include removal from safety-sensitive functions and permanent disqualification from service.
The .10 percent
legal limit is a much more serious violation under criminal law. It is a felony under 18 U.S. Code §342 to operate a
common carrier under influence:
342 - Operation of a common carrier under the influence of alcohol or drugs
Whoever operates or directs the operation of a common carrier while under the influence of alcohol or any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802)), shall be imprisoned not more than fifteen years or fined under this title, or both.
343 - Presumptions
For purposes of this chapter -
(1) an individual with a blood alcohol content of .10 percent or more shall be presumed to be under the influence of alcohol; ...
Unlike FARs, you are subject to serious jail time for violating §342.
Criminal complaints under §342 are initiated by law enforcement officers, typically a Special Agent for the DOT.
In summary:
- Violate FAR 120.37 == lose your job
- Violate 18 US 342 == go to jail