Just a few comments to supplement RadioGirl's post. (Yes, also my first post on the site!)
Inmarsat operates a few generations of Satellites. The I-3 ones have 4-6 spot beams each, which in total cover the same area shown in the Inmarsat coverage maps others posted. The I-4 sats have 19 regional beams (several hundred kilometers wide), but the question is which sat was used.
As noted, a range calculation will give you a circle centered on the satellite. However, there are presumably many data points from the satellite, not just the final one. If you assume the plane is flying a generally straight path (i.e. forming a tangent line to the circle corresponding to the closest it got to the satellite), its distance to the satellite will first decrease, then increase, as it hits that point. Add in the military radar plots and you have a starting point, and thus two potential paths (north and south).
Welcome to FT and thanks for your contribution!
Yes, I was trying to do this quickly and keep it simple. From the apparently vague position implication I assumed it was the I-3 birds but maybe more information (including about the distance of the earlier pings) is yet to come to light.
Originally Posted by
invisible
However, if in the article from WSJ it was said:
In the case of the missing Malaysian jetliner, precise locations were provided.
I'd doubt the part 'it has never been done'. See my
previous post about this.
Either way. What I wanted to say: was it possible to deliberately leave SATCOM on, however hack is such a way that it transmitted wrong coordinates?
I agree the WSJ quote is now out of date (possibly the precise location of the transponder being turned off, or of last radar contact) and the precise location of the last satellite contact is not known.
See below about "never been done".
I think it would be difficult to fool the system into transmitting wrong coordinates (James Bond's villains notwithstanding) but in any case it is clear this system was not transmitting any coordinates.
Originally Posted by
Nrg800
This is pure unadulterated speculation, but would it be possible for the plane to land somewhere near the final ping and have the SATCOM link mechanically removed and destroyed, rather than hacking the software involved?
If they've landed, just shutting down the plane should do the same thing. I guess if they know where the satcom antenna is they could disconnect it.
Originally Posted by
alanstarr
I think it is safe to say we should all look at media reports with a huge handful of salt. The guys writing are usually just average folks and they can easily get confused with highly technical data.
True.
Originally Posted by
alanstarr
As for "never been done", I obviously meant it in terms of aviation, i.e. using satellite pings to locate a certain civilian aircraft.
It may be that the Inmarsat system doesn't usually use a time stamp to estimate distance but if the time of arrival and the time stamp of transmission are known, the calculation is very easy. (Time difference * speed of light, then account for satellite altitude.)
If there was no time stamp, but they have an accurate value for received signal
power, they can estimate the off-boresight angle. The bolded contour is where the aircraft looks "up" at 40 degrees above the horizon and the satellite receives 50 degrees from its centre. The uncertainty in estimating that angle could easily equate to the 100 km (?) corridor cited.
Originally Posted by
Kiwi Flyer
Sorry for being unclear. That's what I meant. The last radar/radio contact was fairly close to the satellite ping arc.
I think the proximity to the east side of the curve is coincidence. Assuming (??) that the plane kept flying and assuming (??) that it went in a fairly consistent direction, the obvious place to look is where the satellite contour intercepts the expected flight distance for the corresponding time.
Or they could have landed somewhere for 4 hours and still be in the Malaysian region. Or they could have flown in circles over the Gulf of Thailand for 5 hours. So there's still no absolute reference.
Nrg800, thanks for the maps!!!! ^