What is the difference between the 0.02 and 0.04 BAC limits in FAA drug and alcohol testing?

Under 14 CFR Part 120, a blood alcohol concentration (BAC) of 0.04 or greater is an outright program violation that triggers removal from safety-sensitive functions, a Substance Abuse Professional evaluation, and potential FAA certificate action. A BAC between 0.02 and 0.039 is not a formal violation, but the employee must still be removed from safety-sensitive duties for a minimum of 8 hours. Falling below 0.02 requires no Part 120 action, though the separate 8-hour bottle-to-throttle rule under 14 CFR 91.17 still applies to crewmembers regardless of measured BAC.

How many times does an employee have to be tested after returning to duty following a drug or alcohol violation?

Under 14 CFR Part 120, a Substance Abuse Professional (SAP) must direct at least six unannounced follow-up tests during the first 12 months after a covered employee returns to safety-sensitive functions. The SAP has discretion to extend the follow-up testing period for up to 60 months total. These follow-up tests are required in addition to the employee's continued participation in the employer's random testing pool, so the effective testing frequency is substantially higher than normal.

Does the FAA drug and alcohol testing program under Part 120 apply to small Part 135 charter operators?

Yes. 14 CFR Part 120 applies to all operators certificated under both Part 121 and Part 135, regardless of the size of the operation or the number of employees. A small on-demand charter company with even a single employee performing a safety-sensitive function — such as acting as a pilot or performing maintenance — is fully required to establish and maintain an FAA-approved anti-drug and alcohol misuse prevention program meeting all Part 120 requirements.

Drug and Alcohol Testing Requirements for Commercial Operations

When a pilot transitions from private or recreational flying into commercial operations, the regulatory environment changes dramatically. Drug and alcohol testing is no longer a matter of personal judgment — it becomes a federally mandated, employer-administered program with strict timelines, defined thresholds, and career-ending consequences for non-compliance. 14 CFR Part 120 is the governing regulation, implementing the Department of Transportation's (DOT) drug and alcohol testing framework within aviation. Every commercial pilot working for a Part 121 or Part 135 certificate holder must understand this framework in detail, both for the FAA Knowledge Test and for professional practice.

Who Is Covered: Safety-Sensitive Functions

Part 120 does not apply to all aviation employees — it targets those performing safety-sensitive functions. These are specifically defined in the regulation and include: acting as a flight crewmember (pilot or flight engineer), performing aircraft maintenance or preventive maintenance, performing aircraft inspection, serving as a flight attendant, performing flight dispatch or flight release duties, and conducting passenger security screening. If your job directly touches the safety of a flight operation, you are a covered employee. This scope extends to contractors performing these functions on behalf of a certificated operator, not just direct-hire employees.

Operators certificated under Part 121 (scheduled air carriers) and Part 135 (commuter and on-demand operations) are both required to establish FAA-approved anti-drug and alcohol misuse prevention programs. There is a common misconception that Part 120 only applies to major airlines — in reality, a two-aircraft charter company operating under Part 135 with a single covered employee is fully subject to these requirements.

The Six Drug Testing Circumstances

DOT drug testing screens for a standard panel of substances including marijuana, cocaine, opioids, amphetamines, and phencyclidine (PCP). Part 120 mandates testing under exactly six circumstances, each triggered by a different operational situation.

Pre-employment: A covered employee must test negative before performing a safety-sensitive function for a new employer for the first time. This test cannot be waived simply because the individual tested recently for a different employer.
Random: Conducted on an unannounced, unpredictable basis throughout the calendar year. The employer uses a scientifically valid random selection method so that every covered employee has an equal statistical probability of selection during each selection period. The FAA establishes a minimum annual testing rate, which has historically been set at 25% of covered employees for drugs and 10% for alcohol under the random testing provisions.
Reasonable suspicion: Initiated when a trained supervisor directly observes behavior or physical appearance that provides specific, contemporaneous, articulable grounds for believing the employee is using prohibited substances. The supervisor must have received DOT-required training to make this call — a general feeling or rumor is not sufficient.
Post-accident: Triggered by certain accidents involving a Part 121 or 135 operation. For alcohol, testing must be completed as soon as practicable but no later than 8 hours after the accident, with a target of completing testing within 2 hours; if testing has not occurred within 2 hours, the employer must document the reasons and continue attempting to obtain the test up to the 8-hour limit. For drugs, the window extends to 32 hours after the accident. If the 8-hour alcohol window passes without a test, the employer must document the reasons and must not conduct the alcohol test — testing after that point is prohibited because the result would no longer be meaningful.
Return-to-duty: Before an employee who has violated the drug or alcohol program may return to performing safety-sensitive functions, they must be evaluated by a Substance Abuse Professional (SAP), complete any recommended education or treatment, and produce a negative return-to-duty test result. This is not optional and cannot be skipped regardless of the employee's seniority or record.
Follow-up: After successfully completing return-to-duty requirements, the SAP directs a minimum of six unannounced follow-up tests in the first 12 months of returning to safety-sensitive duties. The SAP may require testing for up to 60 months. These tests are in addition to the random testing pool — the employee is subject to both simultaneously.

Alcohol Testing Thresholds and Rules

Alcohol testing under Part 120 operates with a tiered threshold system that is distinct from — but related to — the longstanding crewmember rule found in 14 CFR 91.17.

0.04 BAC or greater: This is an outright violation of Part 120. An employee who tests at or above 0.04 blood alcohol concentration (BAC) is immediately prohibited from performing safety-sensitive functions. This is the same BAC limit referenced in 14 CFR 91.17 for acting as a crewmember.
0.02 to 0.039 BAC: This range does not constitute a program violation but still requires action. The employee must be removed from safety-sensitive duties for a minimum of 8 hours. No SAP evaluation or return-to-duty process is triggered — the employee simply sits out the minimum period and may then return if retested below 0.02, or after 8 hours have elapsed, depending on employer policy.
Below 0.02 BAC: No action required under Part 120.

Separately, 14 CFR 91.17 applies to all flight operations — not just those under Parts 121 and 135 — and prohibits any crewmember from acting in that capacity within 8 hours after consuming alcohol, while under the influence of alcohol (regardless of measured BAC), or with a BAC of 0.04 or greater. These two sets of rules overlap but are not identical. A pilot who had a drink seven hours ago and tests at 0.01 BAC has not violated 91.17's BAC limit, but is still inside the 8-hour bottle-to-throttle window and may not fly.

Memory Aid

The 0 / 0.02 / 0.04 ladder summarizes the alcohol hierarchy: Zero alcohol within 8 hours of flight (91.17 time rule); 0.02 means removal from duty temporarily (Part 120 action level); 0.04 is an outright violation (both 91.17 and Part 120). Each rung carries increasingly severe consequences.

Consequences of Violations and Refusals

The consequences of a positive test or a program violation are serious and multifaceted. An employee who tests positive, or who refuses to submit to a required test, is immediately removed from all safety-sensitive functions. Critically, refusal is treated identically to a positive result — there is no lesser penalty for simply declining to test. A refusal includes not only outright declination but also conduct that obstructs the testing process, such as failing to appear at the collection site, adulterating or substituting a specimen, or leaving the scene of an accident before testing is completed.

On the certificate action side, the FAA may pursue suspension or revocation of an airman certificate. The FAA's Drug Abatement Division maintains records of violations, and employers are required to report them. Any future employer within the DOT-regulated transportation industry must query the FAA's records and contact previous employers from the past two years before allowing a new hire to perform safety-sensitive functions. A violation follows a pilot across employers and across transportation modes. Furthermore, positive drug tests and certain alcohol violations must be disclosed on FAA medical applications — failure to do so truthfully is itself a federal offense under 49 USC that can result in certificate revocation.

Key Numbers and Rules Summary

Part 120 applies to all Part 121 and Part 135 operators, including small on-demand charter companies.
Six testing circumstances: pre-employment, random, reasonable suspicion, post-accident, return-to-duty, and follow-up.
Post-accident alcohol testing window: target completion within 2 hours, hard cutoff at 8 hours with documentation required if the test is not completed by then; drugs must be tested within 32 hours.
BAC of 0.04 or above = program violation (Part 120) and crewmember prohibition (91.17).
BAC of 0.02–0.039 = removal from duty for minimum 8 hours, no formal violation.
8 hours bottle to throttle applies across all operations under 91.17, regardless of measured BAC.
Minimum follow-up testing: 6 unannounced tests in the first 12 months; SAP may extend up to 60 months.
Refusal = positive test result in terms of consequences — no exceptions.

Common Test Traps

The 8-hour rule and the 0.04 BAC rule are independent obligations. Satisfying one does not automatically satisfy the other. A pilot could be outside the 8-hour window but still have a BAC at or above 0.04 — both prohibitions must be independently met before acting as crewmember.
Refusal is not a lesser offense. Many students assume that refusing a test is better than failing one. Under Part 120, both outcomes carry identical immediate and long-term consequences.
Post-accident windows are substance-specific. Alcohol has an 8-hour hard cutoff (with a 2-hour target and documentation requirement); drugs have a 32-hour window. Do not apply the same number to both.
The 0.02 removal level is not a violation. An employee at 0.02–0.039 must be removed from duty but has not committed a program violation requiring SAP evaluation — this distinction appears on the Knowledge Test.
Part 120 covers Part 135, not just Part 121. The on-demand or commuter context does not reduce or eliminate the employer's obligations under this regulation.
Follow-up testing supplements — it does not replace — random testing. A returning employee is simultaneously subject to follow-up and random pools, increasing their effective testing frequency significantly.