From a Washinton Post article:
"...Those limitations are known, but a new analysis estimates the tipping point at which Starlink connections could bog down: With as few as 419 Starlink customers in an area the size of Tacoma, Washington, service for all users in the area could become unusable...."
I guess from this Starlink will generally be good in flight, but be a mess near/at relatively busy UA airports when fully-implemented.