The latest incident occurred on September 6, when the first officer was removed from the aircraft before its scheduled departure for Delhi after authorities suspected that he had consumed alcohol.
The primary test reportedly indicated the presence of alcohol, while the result of the secondary test is awaited.
As the secondary report remains pending, the suspended pilot was repatriated to Delhi as a passenger.
Air India reiterates zero-tolerance policy
Air India said in a statement quoted by NDTV: "Air India maintains a zero-tolerance policy towards any violation of safety, regulatory or company protocols. Any confirmed breach is dealt with firmly and action in accordance with regulatory requirements and company policy is enforced."
"To reinforce a culture of discipline, compliance and accountability, Air India has reiterated to all flight crew the critical responsibility of operating to the highest standards of safety, professionalism and integrity.
"The airline conducts regular awareness and compliance training, mandates testing for psychoactive substances, and enforces strict disciplinary measures that may go beyond minimum regulatory requirements."
Weeks after Phuket-Delhi marijuana case
The latest incident comes weeks after an Air India Phuket-Delhi flight encountered a sudden altitude loss on August 4.
The Airbus A320 involved was carrying 137 passengers and eight crew members. The aircraft experienced a sudden altitude variation of around 300 feet during cruise, injuring 20 passengers and four cabin crew members.
Both pilots underwent mandatory psychoactive-substance screening after the incident.
The pilot-in-command's initial test returned a "non-negative" result, requiring confirmatory testing. The subsequent confirmatory test was reported as positive for marijuana.
The Aircraft Accident Investigation Bureau (AAIB) is investigating the incident. Its preliminary findings also identified a brief failure of all three hydraulic systems on the aircraft. The investigation has not established that the pilot's drug-test result caused the aircraft's altitude loss.