Are all peer reviews/pull requests equal?
A lot depends on the size, maturity, and customers of the group shipping code. One-person side/hobby projects wouldn't have a 2nd person to review the code. A previous employer initially had a "Deploy to Production" script that ran every 60 seconds, copying the Development folder to the Production folder - to make easier their testing in Prod.
But large publicly-held companies with more customers will often have auditors that require better controls over dev/test/UAT/Prod, and between developers and operators. Separation of Duties is essential to protecting Business Operations from disruptions caused by a single individual.
There should be some sort of lockout that requires 2 humans to put an airplane in the air - at least for major airlines, and could be mandated by law. This could range from a 2-key fuel shutoff for the engines, to different keys on the outer plane door and the inner cockpit door, to mandatory wheel boots on idle airplanes. And part of this would be a very good key management system, possibly with many physical keys managed by an airport or airline "key desk" - or maybe through electronic key-cards, RFID chips or key-fobs, or a smartphone app.