“Do your own research” is a phrase with a lot of baggage. It means more than doing your own research.
It’s a phrase that has been used online in debates over every kind of conspiracy theory, religious idea, or political stance and carries with it the unsaid presumption that alternative sources are the key to learning the “actual truth.” It’s a loaded phrase that acts as a calling card for people who are overly confident that they have the right answer but can’t articulate how they arrived at it.
I roll my eyes whenever I read or hear someone say “do your own research” because I know the debate ends there and there’s no convincing them otherwise.
This is not true at all. You’re right that planes aren’t like cars, but airlines absolutely do their own maintenance. The maintenance program is initially provided by Boeing and modified by the airline based on statistical monitoring of issues.