Right then ,another anomaly;again from the Racal and Mitchell reports;
The Aldergrove QNH was given as 990 mb,Portree 990-991,and I believe as found on the a/c altimeters. The QNH input to the S-TANS is given as 998mb.
The derivation of the surface and altitude winds comes from an encoding altimeter ,fed to the S-TANS and modified by it`s QNH setting; the encoding altimeter gives a Pressure Altitude,based on 1013.25 mb,and then corrected using an algorithm,depending on altitude,but for our purposes 1mb= 29 ft.
Again assuming the ALDG/PORT QNH was pretty accurate , Sea-level pressure was 990mb,with a pressure altitude of 674 ft( ie 1013.25 datum was 674 ft below sea-level.
According to the reports Racal determined that the PA of the a/c at waypoint change was given as 900ft,which they worked out ,using the QNH set to give an a/c altitude of 468 ft. BUT,this was based on the set QNH of 998 mb.The difference between actual QNH is 8mb or 232 ft....
So ,if we take a PA of 900 ft,and a PA datum of -674 ft(below sea-level) we arrive at 230 ft above sea-level.
The Baro metric altitude according to Racal was 468 ft (above the 998 mb datum)(232 ft below sea-level).
That gives an altitude of 236 ft above sea-level ......
At power-down the PA is recorded as being 1100 ft; however this may have been affected by the actual crash conditions as the actual PA of the crash-site at 810 ft above sea-level should have been 810 +674 =1484ft.
However , there is a significant error in PA and it has been assumed that the aircraft had only climbed appx 200 ft or so in the time from the waypoint change to impact ,about 20 secs.
I assumed that the encoding altimeter for S-TANS is the main a/c one which would also possibly feed the TXPDR,or it maybe a separate one. Would anyone know if the instruments were examined in depth as part of the AAIB investigation ?
By my assumptions then,if the a/c was at about 240 ft at waypoint change,and crashed at 810 ft 20 secs later,it must have had a rate of climb of some 1710 ft/min,which according to the reports is extremely unlikely.
Now,I`m not a genius at maths(not even an `O`Level),so if I`ve got the sums wrong,please tell me,and any other answer...... Syc....