|Quoting WingedMigrator (Reply 242):|
Point of order: we only have the last ping ring from Inmarsat. The other colors are quite pretty, but calculated based on unknown assumptions.
These graphs are pretty but worthless : They try to fit the last 18:11 ping with a set of fixed
speed trajectories which also originate from a point said to be latest known position
The reasoning is in error in two very important areas :
1/- choosing a fixed origin defeats the ping-derived loci ( Note that there is no attempt from the author to determine a route, or a series of routes that could fit all loci. To find one would be a miracle.
2/- Choosing a set of fixed speeds, if good for an explanation of the analysis invoved, is in fact patently wrong because
2.1 - the effect of wind on drift ( change of direction of the trajectory ) and speed ( the Doppler shifts are based on ground speed,and no other
is ignored, or left aside.
Taking the winds aloft values for the day, provided by Tim Vasquez, the latest estimated point would have had a 230° /110 kt wind, which entails a drift of 12° left and a ground speed of 390 klt for a heading of 180°TRUE.
So these constant speeds trajectories are a fallacy.
They're good for an initial simplified understanding of the basic principles of a demonstration, but nothing else and nothing more.
2.2 - The endurance of the aircraft at these different speeds is ignored, meaning that according to the author, it went down, even if it had more fuel left.
REASONABILITY CHECK :
A modern airliner can navigate only on three basic principles on an oceanic flight :
(A) - A waypoint-to-waypoint trajectory : it's an orthodrome or arc of a great circle. It necessitates a working FMGS to ride over the IRU data with the help or not of a GPS
... the airplane would still be subjected to the wind effect with varying ground speeds
(B) - A constant TRUE heading reference, which is quite unlikely as we only use TRUE reference at high latitudes -generally around 80° of latitude, North or South : We should see the effect of the winds aloft with varying ground speeds and varying courses due to the varying drifts.
(C) - A constant MAG (netic) heading : here we'll see the aircraft is subjected to the wind - drift and ground speed - and the rapidly changing magnetic declinations.
To illustrate this point, imagine a MAG heading of 180° with a declination of 15°W at the estimated 20:11 locus : This means that the aircraft is in fact flying a TRUE heading of 165°, at which, subjected to a 230° / 110 kt wind, its course would be 150° and its ground speed 415 kt... That's 30° away from a TRUE 180° heading and a 35 kt slower speed.
(D) - Please note : There is no such thing as an *inertial track