AF 447 Search to resume

[JD-EE]

HN39, the analysis is not quite so easy as to admit a precise angle.

If I presume there is no navigational feedback to the antenna aiming algorithms a gentle roll that leaves the antenna no more than (conservative bogey number) tilted less than about 75 degrees will be tracked and communications can transpire. A rapid roll would destroy antenna lock once the antenna fell out of the beam - say 40 to 50 degrees of roll even if the beam could be steered to point to the satellite. If there is navigational feedback then you're back to the the detail that the antenna cannot effectively steer to smaller angles to its plane than 15 degrees or so. (Somebody familiar with polar routes may correct me on precisely what latitude is the limit for SatCom capability on aircraft. My experience is with land/maritime SatCom and I know that works adequately down at angles around 10-15 degrees. That's with physically steerable antennas, though.)

I believe navigational aiding exists for the antenna. So I suspect that a rather dramatic event would be required to shadow the satellite. My memory insists the pertinent satellite was somewhere "roughly" near the African coastline. So I'd expect such an unfortunate event to be a roll with left wing down in this case, perhaps after the plane was oriented well off course to the North. ("Oh Shirt! What's that!" as the pilot pushes stick forward and to the left to avoid that suddenly appearing bright light ahead of the plane getting larger fast. (Grumble) We cannot even rule out a UFO sighting and a move to avoid striking it. Ball lightning does freaky things.)

I didn't answer your comment with a number. But I hope the data above helps visualize what it would likely take.

Machinbird....
The downside to a conspiracy for BEA is high with regards to exposure and loss of faith in France, French airlines, and French airframes. That's so high a risk it's hard to envision them taking it.

I can envision then "cheaping out". One airframe saved is XXX megabucks. That loss has some small probability per year. (Decades before one plane went down in these circumstances?) What's the cost in airframes per year for continued search? The risk of "cheaping out" is much the same as above, though. So they are under immense pressure from two sides to not only solve it but to solve it cheaply. I can understand there being considerable deliberation before spending more money in bulk measure.

Regarding nav aid - I am SURE the antenna can self track the satellite. The marine antennas I worked on tracked fairly easily. Once I rewrote the algorithm I had a lab unit tracking within 0.1dB (about 3%) of the peak signal. I described a square in the sky. I moved it until the signal level from all four corners was equal. I then knew the antenna was pointed very near the satellite at any given time Precise pointing was worth that fraction of a decibel in signal level. The antenna itself had accelerometers that allowed it to track in remarkably rough sea states.

For the airborne antenna the antenna gain is less meaning it has a wider beamwidth. In fact it is so wide that a simple navigation feed from the plane can keep the antenna aimed properly. Attitude feedback can ensure lock even if the plane is tilted. I'd expect that. I can't guarantee that it is there. Again, it's such a simple thing to add that correction to the antenna aim that the thought of not doing it feels "dirty" to me. If it comes rapidly enough, say once every 10 seconds or less, it'd take a REALLY violent move on the part of the plane to make communications impossible.