how it could be cont.
posts from Sergey Amielin blog made by Tomasz tu154 pilot
"I have confirmed information that the pilots of Tu-154 and their colleagues from the 36th Special Transport Aviation Regiment routinely used the non-WGS-84/PZ-90.02-compliant coordinates (runway threshold) given on the Smolensk instrument approach charts. They should not if the FMS was set to WGS-84. Evidently their training was lacking in that area."
"The error estimated was 180 m east-west and 30-40 m north-south. That explains why the aircraft was 40 m south of runway's extended centerline - it was pefectly tracking runway's extended centerline to the runway threshold. The crew had the distance from the threshold - the indicated distance ws 180 m shorter than the real one - but it is irrelevant to the crash - this position error is not significant enough "
"One should not expect better guaranted accuracy than 550 m (0.3 NM) with GPS RAIM anyway. Unfortunately their vertical navigation was much less perfect."
"I have made an analysis of possible Tu-154 approach profiles with use of available flight simulator and I am now leaning towards the third primary reason, not mentioned by me before - barometric altimeter setting error. I don't know who made the error - controller or pilots, if this theory is right. Simple entering QFE value 759 mm Hg instead of 749 mm Hg would put the aircraft 120 m lower than intended by the crew."
"It seems to me a bit less likely now, that the crew intentionally doubled the rate of descent, being as close to the ground as 100 m above aerodrome threshold, because it seems to be contrary to common sense of majority of airmen. Possibly, they could have believed, according to the baro-altimeters (with wrong QFE) that they were high on the glidepath (virtual, since no glideslope existed) and close to the Inner NDB."
"That's why they increased rate of descent trying to reach MDH shortly before Inner NDB or over it. Unfortunately the RA altitude callouts could have been unavailable, due to TAWS inhibition by the crew (depending on type of TAWS) caused by lack of XUBS airbase in TAWS airport database - possibly they never included scan of the RA - maybe it was intented later, after passing Inner NDB, as I previously noted, providing they had ever considered going below MDA. Maybe they never intended to go below MDH."
"On the other hand you don't try approach with 400 m visibility and 120 m MDH. The success, even without considering the tragic approach lights technical condition, was unlikely, without ducking under MDA close to the Mised Approach Point. Maybe they had reason to believe that the visibility had been better than reported. Or maybe they just wanted to close the mouth of their supervisors ungry that they didn't give a try. Definitely there was lot of pressure (even if not spoken verbally)."
"Staying high on glidepath could be misleading to the controller, who was not aware of wrong altimeter setting or anything else going bad, until they increased the rate of descent. Increasing rate of descent at about 2 km from the threshold, when you know you are in heavy jet just 100 m above the ground is a bit strange to me - however if they wanted to try really hard and had never thought about the lower terrain 1.5 km from the threshold"
"(I bet they were not aware of its existance - you don't see such insignificant things during approach in VMC), they just had concentrated on RA and artificial horizon and pressed on, however the pilot monitoring should be looking occasionally outside. Likely he saw the ground just two or three seconds too late."
"Regarding the wrong QFE the question is whether the error was made by the controller or by the crew, and exact circumstances of the error making. And no doubt, it always unsafe when you mix QFE with QNH, mm of HG with of hPa, and meters with feet, especially if you are accustomed to QNH, hPa and feet, because it always adds some unneccessary confusion and distraction."