It's no secret that the crashes of two Boeing 737 MAX aircraft have put the U.S. airline industry in a tailspin. In the wake of the tragic crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302--killing all 346 passengers and crew onboard--the FAA grounded the 737 MAX on March 13, 2019.

The airlines that have the 737 MAX in their fleets are feeling the pain of this grounding, losing millions of dollars. In the case of American Airlines alone, 115 flights are being canceled each day due to the Boeing 737 MAX fiasco. United and Southwest have also had to cancel numerous flights each day.

Yesterday, in a CNBC interview, United Airlines CEO Oscar Munoz explained that he personally doesn't know when Boeing will develop a fix that will get the grounded 737 MAX aircraft back in the air. Said Munoz,

We do not know yet, safety is by far you will hear me repeat this constantly as all of us will. It is the most important part of it. So right now it [July] is our best projection and I think everyone has their own. So we really have no sense of it at this point in time.

Unfortunately, that fix--which was expected to be developed quickly--was recently delayed by Boeing. According to an FAA statement,

The FAA expects to receive Boeing's final package of its software enhancement over the coming weeks for FAA approval. Time is needed for additional work by Boeing as the result of an ongoing review of the 737 MAX Flight Control System to ensure that Boeing has identified and appropriately addressed all pertinent issues.

Of course, there's no guarantee that the fix will actually arrive on its new schedule, or that it will work to the FAA's satisfaction, much less the satisfaction of regulators in other countries. It now appears the fixes won't be fully tested and approved before summer.

Oscar Munoz is optimistic that a fix won't be long in coming, but that its rollout will need to be coordinated worldwide. Said Munoz in the CNBC interview,

I think it is important when we return this aircraft to flight that we do it in relative unison and lockstep around not just the U.S. but the world. I think that is an important part of it so we need to monitor and engage that.

Of course, safety is United's first priority. Continued Munoz,

We are not letting our customers and our employees on an aircraft that we don't find safe. And so, we will have to reassure them. And if people do have concerns we will always take care of our customers in some way.

It's going to be interesting to see what happens when the Boeing 737 MAX is returned to service. Will passengers avoid flying on it? Only time will tell.