Anything but an expert - can I ask, what does "Disappeared from radar" actually mean? The plane descended from cruising level to surface level in less time than it takes for a radar dish to rotate once?

Radar is, essentially, line-of-sight. An aircraft doesn't have necessarily to be at sea level before it's invisible to radar.

https://en.wikipedia.org/wiki/Radar_horizon

So an aircraft should be visible down to sea level around 20 nm from Guernsey's radar head, and around 43.5 nm if at 500' altitude.

C52, . what was said was radar contact was lost from the radar display which the controller was looking at when controlling the aircraft.
Many possible reasons for that : you can put any filter on your display being altitude or garbling filters at low level., but that said a normal APP SSR radar , can detect transponder replies quite low over the sea . A primary radar is more likely to have a filter a low altitude to avoid picking up windmills and ships..
I do not think the aircraft "disappeared" from all radars around, and they are quite a few.
It could indeed have picked up ice, stalled and dived down quickly,
The other possibility besides icing is that it could have had a major failure , i.e electric which would explain the sudden stoppage of the transponder and absence of mayday call.

Assuming we are talking about Jersey Radar (happy to be corrected if not) then I believe it is SSR only. See Replacement of Air Traffic Control Radar

19 August 2016
A 6-month project to remove the old primary radar and replace the secondary radar system along the Island's north coast is due to begin week commencing 22 August 2016. Although both primary and secondary radar systems are currently used by Jersey Airport the reliance on the former has decreased over the years and it also conflicts with the island's 4G mobile phone system. The decision has been taken to remove this primary radar and upgrade the secondary radar.

An aircraft could still be in the Designated Operational Coverage area (“in cover”) and not be ‘seen’ for several reasons. E.g. transponder switched off or unserviceable.

That crossed my mind too!

TRUTHSEEKER ...Yes, that's what I said re. glide distance, I estimated glide distance to be about 2 miles for each 1,000 feet of height had, given that there were only two on board ... we agree then.
My point was more to do with this pilot apparently not considering staying over land for as long as possible, thus making the intended channel crossing as short as possible. This wouldn't have taken the plane far off of it's direct route, the route it looks like it took and which led to the plane being over the open sea when whatever problem occurred. It appears that had he done this (and assuming an engine failure was the problem), then he would probably have been able to make a forced landing on the French mainland ... not an easy thing to do at night of course but a far better option than being forced to ditch in the open sea.
If it was some kind of structural failure which occurred then there was nothing that could have been done of course but the chances of that occurring are statistically very small indeed.

Luc Lion ... I agree with what you say about flying IFR at a sensible height in this situation and as you say, if the de-icing equipment was u/s or the pilot unfamiliar with its use then then it would have been irresponsible of the pilot to go ahead with that IFR flight. It seems he wanted to fly VFR though and it is this which has me make the point on him staying over land for as long as possible ... see my original post ... but even this is only ok for so long ... the min. 60 mile Channel crossing still has to be made and it seems daft to plan to make that crossing at 2000 feet ... or even 5000 feet, in a single engined aircraft.

At this point it would seem that no one (outside of investigators & ATC) has any idea what the actual routing was? Mention's of Burhou Island & Casquets have been in some reports so on that basis I doubt it was just a 'point and go' flightplan. My guess is the BRILL waypoint / Casquets VRP was on the Flightplan ( depending on the STATUS of the Flightplan? ).

ATC Watcher .... There seem to be many possibilities for this tragedy and the fact that no Mayday call was made (?) is significant. One possibility could be that the pilot had a massive heart attack for example ... this would certainly explain the absence of a Mayday call. But the icing which you mention as a possibility seems very unlikely to me. If the aircraft had been at 5000 feet and then descended to around 2,300 feet as reported, and I assume it was travelling at cruise speed, is it likely that icing would have caused a stall? Yes, had he been at low airspeed, for example on an approach, I could see that as a possibility but for an aircraft to stall due to ice build up, at a cruising speed of around 170 knots+ at that height ... I doubt that ... but then I'm no expert. A massive build up of ice could cause the stall you refer to but is this massive build up likely in that location at that time and at that height?
I have no idea what the weather reports said for that time, have you read anything on this matter?

my bet , Its spacial disorientation . PPL no instrument rating , night , cloud , no visual horizon . A very sad and avoidable tragedy .

Rather close to the knucle I`d have thought, particularly given it is coming from a chartered accountant. Must remember this is a public forum and one`s got to know a willie from a winkle for the sake of the Life of Brian. One of my favourites is the chartered accountant lion tamer wannabe sketch.

TRUTHSEEKER ... You are right in saying that the exact route of the aircraft hasn't yet been established. I have assumed and perhaps wrongly, that it flew from Nantes to the reported point of its loss in a straight line, as if we extend that line it appears that it lines up perfectly with Cardiff in Wales, his destination of course.
I wasn't suggesting that there was the possibility that the aircraft had made it to land, it seems that the plane went into the sea to the west of Alderney ... I said that had the pilot chosen to stay over land for as long as possible instead of possibly making a direct flight to Cardiff and which took him over the sea for much of it, then given where the plane was reported to be when contact was lost, they would have found themselves over land or at least within gliding distance of it and capable of making a forced landing in France.
To be clear, had the pilot flown almost directly north from Nantes he'd have been at approximately the same latitude as that indicated by reports of where the plane was 'lost', to the west of Alderney, and still over land. As I've said, this would also have given him the shortest possible Channel crossing, i.e. around 60 miles, changing his heading for Portland in Dorset once he'd started his flight over the Channel.

Have the timelines become public knowledge of exactly what time Emiliano Sala was sending the whatsapp message where the message included the aircraft was shaking?
Has anyone mentioned whether they know whether Emiliano Sala took the Co-pilot seat or whether he was sitting in the club seating area?

Has Dave Henderson reappeared yet? his insight into the movements of N264DB might hold the key to a lot of unanswered questions.

keni010,
Taking the straight line ( as near as dammit ) highlights that 2 sectors of notable water crossing of 52nm & 74nm would be planned.

I have to say that up until now I wouldn't have given a second thought about doing a straightline journey between Nantes and Cardiff, I would have used the 89nm initial sector to get a bit of altitude though, however I have seen VFR pilots who would stay VFR if the cloudbase was 5000ft or less as long as the MSA was below the base of the cloud.

The big question is : " Would you think it is safer for a VFR pilot to go up into IMC than try to stay VFR below the crud? This again is a supposition because it is unknown whether Dave Ibbotson has an IMC or Instrument Rating?

There are so many unanswered questions that are being answered by differing scenario's that it might be better if we all now wait for the Authorities findings & reports to be published.

https://cimg9.ibsrv.net/gimg/pprune....b8f9ced081.jpg

On an AOC trip today an operator's pilots were asked, by the passengers, "in the light of recent events", to show their licenses !!!!

Truthseaker1
 

Plenty of pilots with commercial licenses and IR's doing dodgy charter, it's the AOC certificate the passengers need to see. While a commercial license (or ATPL) assures a certain level of knowledge and training the full legal protection is given by the AOC, and on an AOC flight if you aren't at least a CPL you're not sitting in the pilot's seat. I have no doubt the pilots of the Eclipse that flew Sala to Cardiff were commercially licensed, what I doubt is that it was an AOC flight, and therefore, probably as legally dubious as the PA46 flight.

I fly for an AOC, most of the brokers who use us have our AOC certificate and insurance on file, direct customers get a copies with their written charter agreement. That certificate takes some getting, is very easy to lose, is expensive, has specifically named personnel as post holders, all of whom qualify for the positions they hold and are accountable in law. The pilots operate to an accepted Operations Manual, and their duty and training records are subject to both internal and external audit, along with SMS, mandatory maintenance contracts, and sometimes, at our expense we are audited by organisations such as Wyvern, who audit us on behalf of large corporations and key man insurers to ensure we are up to snuff.

Basically the same procedures and licensing processes as BA, Virgin, EasyJet, Tui, FlyBe and all the rest, but in a company a fraction of the size. I'm one of the post holders and sometimes when I'm drowning in paperwork, regulated to a high shine I see the "illegal" operators around and have to fight back a huge temptation to beat the pilots to death with the Ops Manual. What stops me is that a criminal record would make AOC employment a touch difficult, and I couldn't drop my standards to where those pilots are.

SND

TRUTHSEEKER ... Thanks for that ... the only experience I have of crossing the Channel is many times from around Folkstone to Cap Griz Nez ...the old LAC (Light Aircraft Corridor) so long trips over the sea were never part of my flying ... though I did once fly almost directly from Ostend to Southend (EGMC) ... I was very young at the time and should never have done that in my opinion now. I believe in keeping sea crossings as short as possible and having the height to glide to land from mid channel for example. When I was in my early twenties I didn't really think about this much and used to cross the Channel at 3000 feet. This would only have given me around 8 or 9 miles of glide in a PA28 according to what I was told back then, though I have subsequently learned that this was probably a little optimistic? Possibly 6 or 7 miles with 2 on board and full tanks. (Tanks filled in order to get the customs drawback on the fuel.)
You mentioned in an earlier post that Casquets Island had been referred to in regard to the route taken by this plane. Overflying this island or thereabouts, would be on a direct flight path to Cardiff.