Originally Posted by
skylane
In heavily trafficked routes, yes, ATC will dictate the route and altitude (standard terminal arrivals and departures for example). Typically the pilot files a route/altitude and then ATC will either grant it or provide an alternate clearance.
To add to this, in the case of the major airline it's a computer/dispatcher that files the flight plan, and generally, the most favorable cruising altitude economy-wise would be filed (depending on restrictions). Of course the pilots have discretion and can request another altitude, but otherwise, ATC would generally assign the filed altitude if other traffic or circumstances don't get it in the way. Based on the FlightAware data it looked like a request for lower cruising altitudes was filed by UA's dispatch.
Originally Posted by
skylane
The assigned route was BNDTO5 MNURE WLEEE4. The BNDTO5 MNURE has a standard altitude of 16000.
I believe FlightAware shows the filed route rather than the assigned route. In any case, this procedure hasn't been changed since 2015 so in itself wouldn't be cause for any recent change. ATC is free to deviate and assign higher altitudes, traffic and other restrictions permitting.
WX could certainly be a factor. FAA is also trialing noise reductions with slower departures which results in slower climbs and for a very short flight would result in a lower cruise altitude (there's a story about Boston,
WSJ paywall).