TODAY | April 21, 2014
>>> this is day 45 in the hunt for malaysia airlines flight 370. for an eighth time, a robotic submarine scanning the search area has come up empty, and passengers' relatives are again voicing frustration after meeting with some officials over the weekend. nbc's katy tur is in perth, australia. katy, good morning to you.
>> reporter: good morning, matt. bluefin-21 is right now on its ninth dive. so far it scanned about 2/3 of the underwater search zone with nothing to show for it. this as officials say that right now, they are at a very critical juncture. by the end of this week, searchers say they will be done mapping out the underwater area where they think the plane is located, based on those four acoustic signals heard more than 13 days ago. those pings went silent last week. still, experts say that investigations like this are constantly evolving.
>> we have to remember that in the search for air france 447, it took them 18 missions to finally find the wreckage of that airplane. they found it ten kilometers away from where they thought it was. and they knew exactly where that plane crashed on the surface.
>> reporter: as it stands, the location of mh-370 is just an educated guess. a frustrating reality for family members. you haven't been searching in the right place, said this man at a meeting with malaysian officials in beijing. in an open letter , loved ones of the 239 passengers wrote, we are in utter outrage, despair, and shock. day 45 and they say their concerns have yet to be addressed. namely, why there has never been any independent peer review of the data. and why they would accept a single source for analysis on where the plane likely went down. now, if they don't find anything by the end of this week, officials say they will need to regroup, reconsider, and decide how to move forward, potentially even reconsider their entire search plan for this plane, matt.