Good luck getting a response from Benson or the majority of military airfields on a Sunday afternoon. However, there is no reason why they could not provide a superb GCA if you could flush the duty ATCO out of the mess.

And like all UK Military airfields Benson have signed up to the Strasser scheme so in a genuine emergency will offer a free landing to any GA aircraft under 3tonnes not flying for hire or reward.

Even on a Sunday, I'd imagine a call on 121.5 would generate an appropriate response.

In that case I'd be self announcing and shooting I-BO if I unexpectedly hit bad weather and low minimums trying to get into Chalgrove.

Benson ATC operates when required, usually on a weekend they only have a TWR service to support UAS & AEF flying.

It is likely that with the appalling weather forcast it is most likely that Benson would have cancelled all UAS & AEF flying and so ATC would have shut up shop and gone home.

An ATC service and an ILS would have been available at Brize Norton.

What's all this talk of diversion, Benson, Chalgrove etc? No one has ascertained where the aircraft was going but draw a straight line on a chart between Turweston and WOD NDB and you'll find the crash site. Those of us who often transit that area beneath the TMA often use WOD as a waypoint.

13/31 is the only licensed runway at Chalgrove. 06/24 and 18/36 are not licensed.

The entire site has been sold by the MoD to/transferred to the HCA with intent to sell it for housing development. Link.

Why would a private GA flight require a licensed runway? The other runways do not have crosses prohibiting their use. The Licensing is for the airfield operator Martin Baker a company World famours for their own IFR let down systems! The licensing is also irrelevant to any military use of the airfield.
It would not be the first time the MOD had attempted to sell land they may not own, Halton and Wittering come to mind!

Do birds fly in fog? very carefully.
 

Sillert asked that question. With thick fog in my garden, the birds are reluctant to fly. Those species that fly in flocks do a lot of squawking to each other, fly in more circles, and closer together when viz is poor. Of course they only have VFR, and a sense of the earth's magnetic fields. The Red Kites that frequent the Chilterns and now points west, are solitary in flight as a rule.

They certainly keep an eye on other air traffic, as we have shared thermals on many occasions.

Is there evidence that the route flown was a straight line track? The M40 runs down that way and the accident appears to have occurred close to where it goes over the ridge.

I believe it was this post that first mentioned Chalgrove as the intended destination. I get the impression that since then, we've all just assumed that information to be accurate.

I find it hard to accept that an experienced instrument rated pilot in an IFR-capable aircraft would have been navigating enroute by attempting to visually follow a ground feature in the Wx prevailing at the time.

If Chalgrove was indeed his destination then I assume he wasn't flying on a clearance which leaves making the flight as you described as they only other option.

As he was outside controlled airspace then no clearance is required. In the UK you may fly IFR outside controlled airspace subject to pilot qualification.

So (and this is pure speculation) the pilot might have flown above safety altitude for the first portion of the flight and then performed some sort of cloud break procedure.

As has been stated previously this accident could be caused by many different factors - pilot incapacitation is a possibility, for example.

Agreed, that is why incapacitation looks like the most likely option as the MSA for that sector is 1400 and the official & witness weather observations were from between clag to the deck to broken 800, so no matter which way you shake it he would have to have descended below MSA in IMC to get to the bases if indeed there were bases to be had.

As fireflybob says, you don't need a clearance to fly IFR in class G in the UK. You do still need some method of visually acquiring the runway environment, whether by means of an approved procedure (there is none for Chalgrove) or otherwise, and the pilot may have been attempting to do this when the accident occurred.

Yes well aware that instrument flying in uncontrolled airspace is legal, pretty much 100% of my IMC flying up here in Scotland is done that way. The hard part is making sure as best you can that you can get a transition to VFR (above MSA) at your destination. Hoping on getting a cloud break stretches the odds out a bit.

I suppose it's possible he was flying into Chalgrove, but in 12+ years of flying out of Benson I've never seen anyone there at all.

Like you Tim I doubt Chalgrove as a destination, scud running along the M40 towards Booker or White Waltham would fit the bill but I guess we will never know for sure but the AAIB will no doubt get as near the truth as posable.

Like you Tim I doubt Chalgrove as a destination

Did he not 'check out' at Turweston? In doing so is not the intention, number on board and endurance declared in that? or have procedures changed? Or is Turweston not a manned field?

I believe under SERA "booking out" is no longer mandatory - in my opinion this is stupid but there was thread running on this a while ago with some people banging on about rights!

I know there is a feeling amongst some that this site has perfect knowledge but perhaps those at the departure airfield know perfectly well the sortie to be flown but just choose not to say... Like most accidents... they are less indicators that there was no plan, just something happened that interfered with the same.