In this video, the captain proclaims after take-off:
We were nervous about this, but takeoff went smoothly
It was his first passenger flight in the A350, but still... not exactly what I would want to hear as a passenger. This got me thinking, does it ever happen that two pilots take their first passenger flight on a given type together, or will it always be the case that if it's someones first time, the other pilot will have X amount of hours on that type?
It is never “the first time”. What he is really saying is that after many hours of flying the aircraft (or an approved simulator) this is the first time doing a revenue flight with passengers. Previous flights would have been training flights.
When a new aircraft type is first introduced to an airline, it can be expected that the entire crew is doing their first revenue flight after training.
What is not expected is that the pilots announce it to the passengers. I would not advise doing that because the passengers might not understand, and it would put doubts in their minds, as it did for you.
Just to point out the obvious:
This got me thinking, does it ever happen that two pilots take their first passenger flight on a given type together
You don't even have to know anything about aviation to be able to answer this question. You can answer this question with common sense and basic logic:
If it's a new aircraft type, then by definition, nobody will ever have flown this particular aircraft type, which means that there must be at least one flight where all of the crew are taking their first flight. It is simply not possible otherwise.
Of course, all of them will have had simulator training on that aircraft type, and all of them will have training flights and checkout flights on that aircraft type, but just by the laws of basic logic, it is impossible for there not to be a flight where the whole crew has never flown a revenue flight with passengers before, simply because there always must be a first flight.
[D]oes it ever happen that two pilots take their first passenger flight on a given type together [...]?
Yes, it does. In fact, it happened in exactly that flight you linked:
Found out that it was the first passenger flight for all of us pilots, but everything went perfect thanks to Scandinavian cooperation and teamwork.
(YouTube video description, emphasis mine)
There is no legal requirement to have any actual experience with passengers on that type. As long as all the pilots have successfully completed the type rating, which includes flight time in the actual aircraft or a level D simulator, and at least the PIC (pilot in command) has the full ATPL (Airline Transport Pilot Licence), which requires at least 1500 hours of flight experience (at least in Europe, not sure about US), there is nothing wrong with that.
Note that based on the other videos in that YouTube channel, the pilot seems to be type rated on the Airbus A330 as well, which is a very similar aircraft. An earlier video Learning To Fly The SAS A350 In Toulouse shows the transition training from the A330:
The one and only simulator session on the transition course from the A330 to the A350. It’s awesome plane.
My answer considers EASA (European) rules.
As a general rule after a transition training in simulator, there is line-flight training in real aircraft. That is flying with (experienced) instructor, although there are passengers onboard. The length of this line-flight training depends on previous experience of the trainee, but it cannot be omitted. After line-flight training there is line check (usually again on actual normal commercial flight) after which the trainee can commence operations without instructor pilot onboard.
In Europe, there is a concept of "in-experienced" crew member. After line-flight training and successfully passed line check, the pilot is considered in-experienced for at least 100 flight hours and 10 sectors. The key idea here is that two crew in-experienced crew members cannot fly together.
So, before two pilots are allowed to operate together, both shall have at least around 120-150 hours of flying the type under their belts.
There are some deviations on this, and most notably airlines can temporarily ignore the in-experienced status when introducing new aircraft types into their fleet. But what they cannot do is skip mandatory line-flight training. It is not uncommon for airlines to buy training for their instructors from other airlines which already operate the type or have instructors from other airlines flying with their newly acquired planes with company pilots.
The case of A350 is little bit different, as it is considered as a "same type" as A330 and they have common type rating endorsement. Many of new A350 pilots are already A330 pilots they can skip some of the line-flight training involved. There is some sim training in between.
With my operator I had couple of flights with instructor when transitioning from A330 to A350. There was no separate line-check or in-experienced status, as I already was active with A330. So I guess in theory it might be that two A330 pilots can fly A350 together after transition course in simulator.
Partial source: https://www.easa.europa.eu/sites/default/files/dfu/Consolidated%20unofficial%20AMC%26GM_Annex%20III%20Part-ORO_0.pdf
For the very first flight of a new type at a given airline, obviously none of the pilots will have flown it with passengers before, though that crew will have undergone extensive training in sims and empty planes. However, that is a very rare case.
In general, a new pilot (either to that type or to the airline as a whole) will only be paired with certain more experienced pilots until their training is deemed complete, so you would never have two green pilots on the same plane.
