Originally Posted by
CBSITCB
How can primary radar returns indicate an aircraft’s instantaneous heading?
It generally doesn't.
It is said MS804 turned 90 degrees left and then 360 degrees right, giving the impression they were balanced turns.
You have injected the word "balanced" which may or may not have been the case. (If the FBW system was operating normally, it probably was. ). Please review this image from
this post based on official information provided by the Greek Defense Minister:
This is a summary of their interpretation of such radar information as they had, so note that it is "possible movements" not "this is God's own truth!"
The primary plot may well have described such a path, but who knows where the nose was pointing?
Considering the summary of information apparently gleaned from radar, and that the staff providing information to their defense minister are not idiots, the general point being made is that the track over the ground (which is what the radar gives you when you track each return) led them to this estimate.
Reviewing Wageslave's post directly above yours, the answer ought to be obvious.
Track information is a collection of data points over time that tell you the aircraft's path over the ground. When an aircraft is flying (rather than falling in a stall or spin) track and "where the nose is pointed" generally coincide. (with a few degrees of crab as needed for cross wind ...)
Couldn’t it have be n ‘tumbling’, inverted, slipping backwards/sideways, etc.? Very unlikely, I admit, but possible?
If you re-read Wageslave's post, and look at the estimate from radar information, a falling tumbling stalled/spun aircraft would have a mostly vertical path, not one that would show what they provided.
From my own experience: years ago, when I was flight instructor, I reviewed radar tapes of an aircraft that had crashed while in a spin. The track information for the maneuvers before spin entry showed the usual time/distance lapse and ground track. The lateral distance covered once spin entry (and the ensuing failure to recover) was significantly less, both on the practice spin initiated and recovered from, and on the subsequent one initiated and not recovered from.
The greater the turn radius the greater the probability the turn was balanced/controlled, but do we know the approximate radius?
The figure above did not try to provide a scale, but none is needed. If it was flying (rather than stalled and falling) then radar track gives a good enough estimate for where the nose was pointed for the analysts to arrive at an estimate of heading.
Again, see the points Wageslave made in the post above yours.