Originally Posted by RatherBeFlying
There is always a chance that the debris triggered a mudslide when impacting on a slope and got buried. Heavy pieces like the engines would be more likely to be buried while lighter parts might "float".
Possible? Yes. Likely? No. I have not ever visited the bottom of the ocean near the mid ocean ridges, but my understanding is that the rocky parts, seen as a rough texture in the bathymetry, are truly rocky, and the sedimentary parts, seen as smooth texture in the bathymetry, are reasonably level. I am guessing that this is due to the slow currents that exist down there slowly levelling things out. I suppose there are some sediment slopes at the margins, but I don't know. So there probably are few places that a landing object could trigger an slide.
Couple that with likelihood that the a/c sank in pieces, spread over at least a couple hundred meters, and there is even less chance that all of it could be covered.
Originally Posted by GarageYears
The side-scan sonar being used now, effectively builds a picture of the ocean floor. So a mudslide could conceivably hide enough of the wreckage to make it unrecognizable? Does that sound feasible?
If some part of the a/c were completely covered, it would not be visible to the type of side scan that is in use. However, a recently triggered slide might itself be visible as a track like a scour mark or a rough area in a smooth field.
Originally Posted by GarageYears
Assuming so, are there other techniques that could be used to search? First thought to pop into my mind - magnetic anomaly detection (MAD). If there enough metallic content to make this a feasible proposition?
Detection of magnetic anomalies requires the sensor to be relatively close to the object being detected, and that object has to be magnetic (either having a permeability different from free space, to perturb the earth's field, or having a magnetic field of its own, i.e. a permanent magnet). The detection distance for a perturbation of earth's field probably requires approaching within 3-10 times the longest dimension of the object.
How many parts of an a/c are magnetic? Not the aluminum or titanium. Likely the engines have enough iron to to be detectable, but at 5m length, you would have to be within 20-50m to detect one. Flying a sensor within 10-20m of the bottom is difficult in this terrain, and flying lines only 20-30m apart, to increase the likelihood of detection would reduce the search rate far below that achieved in phase 3.
Sub-bottom profilers use low frequency sound (a few kHz) to see below the bottom, but they also have narrow coverage in order to have the resolution required to be useful.