S-Works, I believe you are right.
But it doesn't make a difference if the flight was illegal for one reason or for 2, 3 or 5 reasons.
To me, as the flight was organised in the first place, it should have been manned with a CPL (IR) pilot.

"it is good" doesn't mean he had something to pay. Other text messages (with Jack McKay) say that he would have nothing to pay, only help him score a few goals.

But withe a night rating you are still required to have visual reference with the ground. If there are no lights (ie over the sea) and no horizon or sky references then you can be definition only be flying by sole reference to instruments which specifically requires an IR or IMC rating. Under those conditions your rating to fly VMC at night is negated by there being no VMC present.

He was NOT rated to fly an N reg either IMC or at night. Check the FAA airman database yourself. He held an FAA private without Instrument Rating. Even if there turned out to be UK IR(r) or IMC/Night Rating that did not allow him to fly at night outside the UK.

Single pistons are NOT permitted to carry out commercial air transport at night anyway. So I do not see the logic that "it should have been manned with a CPL because it was organised in the first place". And "if it is confirmed that the actual conditions of the flight match private carriage operation" (unlikely) an appropriately rated private pilot would be completely legitimate.

Oggers,
I am talking about FAR 91.501(b)(4) where the operating costs are borne by the operator "for his personal transportation, or the transportation of his guests when no charge, assessment, or fee is made for the transportation". That's private carriage operation.

Either the operator flies himself the aircraft, possibly with a PPL, or he hires a commercial pilot for flying his plane.
I understand that FAR 61.113 forbids any other combination when the plane carries the guests of the operator.
Thus, if Mr McKay had rented that plane and, separately, hired a commercial pilot for flying his guest, the flight would have fit FAA Part 91 under FAR 91.501(b)(4).
Of course, the pilot must NOT be the person renting the plane.

Note: about "was the pilot trained and current for flying in IMC at night ?", I was writing about ability, not legality.

When VFR on top you cannot see the ground either. And VMC only means you will be able to see and avoid other aircraft by their lights, it does not require you see any light of the ground. When flying at night, lights (stars or from the ground) can be a source of spatial disorientation and you should only rely on your instruments. That's why artificial horizon is compulsory for night VFR, isn't it ?

No such thing in EASA land. You may be VMC on top, but, VFR requires sight of the ground, two very different sets of in-flight conditions.

SND

Please explain in a bit more detail why he could not fly an N reg aircraft at night on his FAA PPL. The argument put forward before was that he could not do so because he had no night rating on his base UK licence. Now you say he couldn't do it even with a UK night rating.

Sir Niall Dementia,
even considering you meant Night VFR, your statement that sight of the ground is mandatory is still wrong.
SERA.5005(c)(3) only mandates sight of the ground when the aircraft is below 3000 ft AMSL or 1000 ft above terrain, whichever is higher.

So you can be VMC at night and have to control your airplane by sole reference to the instruments.
A consequence of that is that you must be above 3000 ft AMSL for flying at night in conditions where the sight of the surface is impossible.

Apologies for that, I was thinking of the old rules. BUT re-read the extract above, a1and b rely on flying at speeds allowing avoidance of other traffic or OBSTACLES, OBSTACLES tend to be terrain based, they are rarely hanging around at FL90. The terminology is poor in 5005, but sight of the surface is implicit in the avoidance of obstacle wording. The UK ANO and JAR were clearer on this, SERA 5005 gives intent in it's wording, but needs clarity.

SND

Sir Niall Dementia,
the requirement of flying higher than 1000 ft above terrain (2000 ft in mountainous areas) when not having sight of the surface is also there to ensure that obstacles are not hanging around at altitude.
Grid MORA are there exactly for that purpose.

However, personally, I tend to think that NVFR is there for leisure flights performed in calm clear skies, with the moon providing an eerie lighting.
And for a journey from A to B, at night, the flight should be IFR.
And if an IFR flight can't be made safely under prevailing meteorological conditions, then the flight should be made through an airline.

Mach Tuck, you lost me.
Whom was Mr Sala the guest of ?
And who paid the flight ?
I read interviews of the agent where he stated that he bore the whole costs of the flight.
And I understand that whoever hired the aircraft (on a dry lease) became the operator.

Because, as S Works explained, his EASA medical restricted him to daytime. He had a piggyback FAA private certificate based on his UK licence and all restrictions on the base licence apply.

The bottom line of all this is that despite all the denial merchant/naysayers' rather ludicrous and pathetic attempts to excuse this as being about misunderstandings and misapprehensions of the rules it is abundantly clear that here we have an utterly lawless unlicenced PPL prepared to break any and every rule that gets in his way regardless of ratings, certificates or anything else in order to earn a few quid. Plus habitual hirers willing to employ him and his ilk on a regular basis.
Does anyone believe previous arrangenemts with Henderson were significantly different in legality?
Does anyone actually believe Ibbotson wasn't paid to carry out this job? Really?
Does anyone believe this flight even has a hint, the merest smidgeon of 'cost sharing'about it to apply a veneer of legality about it? Or that it would make it acceptable if it did?
Does anyone believe for a second that the agent didn't know full well that this was a totally buckshee arrangement, or that he hadn't knowingly contracted dozens, if not scores of these illegal trips before?
Does anyone seriously believe that this isn't the merest tiny tip of a huge iceberg of parasitic fake commercial operations going on in full public view with no effort whatsoever being made to stop it?
Wake up!
Get real people!
Puhleese!

There's an elephant in our Cessna 150 that is shattering the public's opinion of GA.
We need to do something about this!

Exactly, maybe now the public will themselves seek out legitimate operators (whom might finally see some fruit for their labours) The strict adherence to the relevant rules and the cost implications thereof has put legitimate operators at a substantial disadvantage to those exploiting the grey area- a grey area that has often been too easily navigated by VFR pilots holding a PPL. I wonder if many realise the sheer amount of documentation (rules, multitude of policies, insurance, worthiness etc.) that genuine operators have to maintain and keep current.

Unfortunately, in this case, the grey area proved to be the undoing of this flight, in more ways than one. Hopefully the conclusions of the investigation into this tragedy will shed some light, provide clarity to all, and prevent all involved in aviation from getting lost in the mist of uncertainty going forward.

Actually S-Works said "He was colourblind and had a specific licence restriction to Day Time Flying ONLY."

Was the restriction on his UK PPL or on his EASA medical? I believe the distinction is important in terms of limitations/restriction that are rolled over to the FAA PPL.