Passenger sees Boeing 757-200 “wing coming apart” mid-air — United flight from San Francisco to Boston makes emergency landing in Denver::A United Airlines flight to Boston was diverted to Denver because of an issue with the plane’s wing.
This is more on the airline not doing their maintenance
Where does it say that the airline didn’t send the plane for maintenance?
Airlines don’t do their own maintenance, they send them back to Boeing.
A plane isn’t like a car, you don’t just have a go at changing the oil or fixing the brakes yourself and then hope for the best, you send it to the approved place when scheduled or you don’t fly.
Where did you get your information that airliners send planes back to Boeing for maintenance? My quick search tells me that they generally don’t, and they either do it themselves, or rely on third parties called Maintenance, Repair and Overhaul (MRO) providers for heavier maintenance. In the case of United airlines, their MRO provider is called United Technical Operations, their own division.
https://www.vanityfair.com/news/2015/11/airplane-maintenance-disturbing-truth
https://simpleflying.com/aircraft-maintenance-checks/
https://en.wikipedia.org/wiki/Aircraft_maintenance_checks
The entire field of reliability-centered maintenance comes right out of aircraft maintenance in the 60s and 70s, term itself was penned by people working for united. It’s responsible for massive improvements in aircraft reliability, there’s a reason that you can point out specific events like this in the modern era.
On a different note, a lot of the guys I worked with out of uni were all aircraft mechanics who had served in the air force.