PKPF68-77
<<… The freak meteorological conditions that appear to have confronted both pilots are described in the following extract from a letter written to the editor of The Daily Telegraph (13 December 2000) by Sqn Ldr Donald Kinch:
“In light winds and high relative humidity, layers of fog and low cloud form adjacent to the Mull to obscure the high ground completely. There are occasions when a relatively calm sea and a grey sky of similar hue merge, so that in otherwise good visibility a pilot flying in accordance with Visual Flight Rules may be unaware that he is about to enter a fog/cloud bank.”
This is an extract from an article about a Neptune crash in October 1956, reportedly about a kilometre from the site of the Chinook crash. >>
Come now, you can have a much more direct input than just a reference like this.
Where you live and with your background, this Summer why not observe the Mull from the sea (do any fishing?) – in a spell of warm afternoons, choose a late afternoon/evening when it is forecast to have the usual southerly at reasonable strength.
Under these conditions, with profiles like the Mull slopes, the lower layer of the air mass gets compressed and therefore speeds up (hence the term for the phenomenon “speed-up”) and reaches the dew point in advance of the bulk of the air mass (which, at a certain altitude, forms the orographic cloud).
Check out the slopes beneath the oro cloud (at the time of the crash, the start of the oro cloud was about 800ft – roughly at the height the a/c crashed).
As the evening cools, the effect becomes more pronounced – and the stronger the onshore wind, the further down the slope from the base of the oro cloud the ground hugging layer of mist starts – and when the wind is very strong (as it was on the day of this crash) the layer can be quite thin, such that intermittently some ground texture can be seen through it. One witness on the ground the evening of the crash described the mist as a layer following the slope, with occasional breaks such that he could see that it was so and described the conditions as common with that wind after that sort of day (this was a local who was also the Procurator Fiscal who called the FAI).
When it extends sufficiently to obscure recognisable objects (eg on the day, the lighthouse was obscured apart from its lower wall) note how hard it is to judge the distance from the landmass – you can see where it is but judging distance off is the problem.
Understanding the local weather is fundamental to understanding this crash:
it eliminates the “official” scenario of pilot error in IMC conditions;
it gives the pilots significantly more time for action to avoid the Mull in the (unlikely, in my opinion) event of control problems as they would have had no doubt as to the direction of the landmass when they made the turn to the right at the position that the waypoint was changed (as opposed to blundering about in fog when problems may have occurred).
Anyone interested in this case has had 13 summers to check this out for themselves – don’t waste the coming one.