A pilot trained to land aircraft in low visibility (CAT III B), travelling as a passenger on IndiGo's Pune-Delhi flight on Saturday morning, was asked to operate the flight as IGI Airport was reporting a declining visibility trend due to smog. Before being let into the flight deck, the pilot underwent the mandatory pre-flight breathalyser test.

from Times of India https://timesofindia.indiatimes.com/business/india-business/cat-iii-trained-captain-flying-as-passenger-asked-to-operate-indigo-flight-as-visibility-drops-at-igi-airport/articleshow/72313106.cms