(CNN) -- When authorities confirmed last month that four "pings" heard in the southern Indian Ocean had nothing to do with Malaysia Airlines Flight 370, it was a devastating blow for those involved in the investigation, the families of those on board the missing jet, and the countless number of people around the world who had become captivated by the mystery surrounding the plane's disappearance.
What was described as "the most promising lead" in the search had proved fruitless.
The investigation into the ill-fated flight is already the most expensive in aviation history. Malaysia has spent $8.6 million so far, Australia is expecting to spend around $84 million, and other countries involved in the search have reportedly set aside sizable sums. Meanwhile, families of the missing passengers are working to raise $5 million to encourage anyone with information about the plane's whereabouts to come forward.
Sunday marked 100 days since the Boeing 777 disappeared. To the frustration and disappointment of many, no tangible evidence has been found. How long will authorities keep working to solve this expensive mystery and what are their reasons for doing so? CNN speaks to aviation experts for their views.
Aviation safety and security
Mary Schiavo, a former inspector general for the U.S. Department of Transportation, says there's a tremendous need to find the plane, particularly if mechanical failure, and not foul play, is to blame.
"The longer time that goes on, the more it appears it was not terrorism, hijacking, sabotage, (or) suicide, and it does appear that something else happened -- something mechanical, some kind of a catastrophic failure, an explosion, something that debilitated the persons on board; and they really need to solve that mystery because until we solve it we can't improve air safety," Schiavo says.
Some improvements have already begun. Malaysia Airlines has changed its cockpit regulations. International aviation bodies such as the International Air Transport Association (IATA) have called on the aviation industry to change aircraft tracking systems.
But convincing the industry to implement safety measures before an accident happens remains a challenge, Schiavo adds.
"In the United States and in many other countries, we legislate by counting bodies. We don't make something the law until someone has died, and that's just awful and unacceptable but that's the way our regulations work," she says.
Maintaining the political will to implement the changes is part of the problem, said David Soucie, a former safety inspector at the U.S. Federal Aviation Administration and author of "Why Planes Crash." Findings can come years after an accident by which time the sense of urgency has subsided.
"Knowing what happened and knowing what could be done to improve a crash investigation, while that's extremely important, often civil aviation authorities make a particular recommendation and it falls on deaf ears because our memories are so short," says Soucie.
In the case of Air France Flight 447, which crashed en route to Paris in June 2009 with 228 people on board, the plane's black boxes weren't recovered until May 2011. French authorities made a series of recommendations, including that the flight recorders' pinger duration should be increased from 30 days to 90 days, but by that time the motivation to do something had dwindled, Soucie says. Since then, some carriers have implemented those adjustments voluntarily but they haven't become mandatory across the industry. Still, the accident did prompt changes in pilot training and Airbus tweaked a key cockpit sensor.
"I'm worried about that with this accident as well -- that the longer we take to find it, the less passionate people are about doing something about what it is that we find," Soucie says.
David Gallo, an oceanographer and Director of Special Projects at the Woods Hole Oceanographic Institution, was involved in the search for Air France Flight 447. He says it's critical to find the wreck soon to prevent a similar accident occurring again, and that the amount of money being set aside for the search is trivial in this context.