Originally Posted by
Lemain
MM43
The TPL is a sort of torpedo-shaped device. Is the 1730m looking along the front centreline, or what? If you think of the search as needing a 'lawn-mower' - i.e. searching in strips - then we'd need to know the strip width and, in hilly terrain, the sensitivity in the vertical axis.
The document referenced above says it's 1730 m lateral to either side of the tow line, accounting for the distance from the TPL to the seabed.
I'm not sure everyone appreciates how big a haystack it is. Uncertainty in the course and speed means that one pass along the arc (without any extremes, just hitting all areas already searched) would be ~1000 nm long. At the maximum towing speed of 5 knots, it takes 8 days to do one sweep.
Now suppose that the aircraft flew for an unknown amount of time between 0 and 20 minutes after the last ping, with the speed of ~400 knots. That would put it between 0 and 250 km from the arc. To cover the entire area with 2*1730 m strips, we need 70 passes, which, at 8 days per pass, would take 1.5 years.
I haven't even begun to consider that the arc itself may be only known with precision up to 100 km (or worse), that the aircraft could have continued flying close to an hour after the last ping (if it had fuel for that), and that it could have glided possibly as far as another 200 km in a random direction after its engines went out.
In this situation, odds of stumbling upon a working pinger without knowing the location of the debris field are so low that SAR understandably tried to find some debris first, then call in the TPL. Calling in the TPL now is a hail mary, with no realistic expectation of it finding anything.