Is he? I can see the number of hours worked as evidence of a shortage, but prima facie it is not obvious that a single controller handling both ground and air is evidence of a 'shortage' if it is routinely considered feasible in the industry. It could just be an efficiency choice for low-traffic times. Based on some googling since I'm not an expert it seems this is called 'position combining' in the US and is pretty routine across the world. Therefore, if this is a problem the primary cause cannot be US policy because non-US airports also do this thing.

Here it's being done at SFO or so it seems: https://data.ntsb.gov/Docket/Document/docBLOB?FileExtension=...

While searching I did find this other document where a GC (LC appears to be Local Control for local air traffic and GC is ground control) controller complains about combining due to short-staffing https://data.ntsb.gov/Docket/Document/docBLOB?ID=19837915&Fi...

Well, it'll be an interesting report from the NTSB at least.

An obvious issue is going to be that while it's supposed to be a lower-traffic time, if you've had delays cascading down the day - it may not be in reality. If the staffing doesn't adjust for delays shifting the time of flights, it would probably often leave you with an overworked controller.

Looking at the normal schedules - if all is on schedule there'd be no departures in the 23:00 hour but you'd still have the arrivals side running pretty heavily. However, once you factor in things not being on schedule, as they evidently were not on that night, you get:

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The 15min before the accident had 14 flight operations (per Juan Browne/blancolirio going through the ADSB playback). And that's in marginal weather and at night, which makes things more complicated.

That is 75% of the official maximum capacity of the airport - during the main part of the day where there's government-imposed caps on flights, it's capped at 74 operations per hour or about 18.5 per 15min.

As such, it seems apparent that you would need just as much staffing (or at least 75% as much) at that time to safely handle the traffic volume that was occurring that night as you did in the main part of the day.

Unless the normal staffing here was just 2 people, it seems clear that 1 is inadequate.

"...routinely considered feasible..."

What we are seeing here is the normalization of deviance.