[FabHK]

> This includes weather and maintenance issues but does not include bumping passengers to allow staff to take their seats.

I'm astonished at the facility with which this keeps being said.

Why are weather and maintenance (e.g. broken seatbelt) a reasonable excuse to bump someone? Well, because they're unpredictable, unavoidable, and if you didn't bump, the flight could not be safely executed, affecting a planeload of pax (and probably more, due to knock-on effects.)

Now, mechanics flying to AOG (aircraft on ground) have the highest priority on many airlines, and dead-heading crew the second highest. Why? Because if they don't go, you will have to cancel flights affecting plane loads of people (and probably more, due to knock on effects). Now, why do you suddenly and unexpectedly have to position mechanics or deadheading crew? Why, good question - frequently for weather, maintenance, sickness, and any number of similar unpredictable and unavoidable reasons.

The justification to bump pax due to seats required for mechanics or deadheading crew is exactly the same (avoid flight cancellation and inconveniencing planeloads of pax that arose for unforeseen, unpredictable, unavoidable reasons).

[fredophile]

Mechanical issues and weather can happen at any time. It's reasonable to assume you could board a plane and then weather conditions change or a fault is identified. Deadheading crew is predictable and can be planned for. United should have been aware of the need for seats for those crew members and involuntarily denied boarding to enough passengers to accommodate them.

[FabHK]

> Deadheading crew is predictable and can be planned for.

But there can be unexpected need for crew to position due to weather, maintenance, sickness.