While nobody knows exactly when the Boeing 737 MAX will be allowed to fly again - the aircraft has been grounded globally since Mid-March - Boeing Chairman, President and CEO Dennis Muilenburg has just announced that Boeing is making ‘steady progress' getting the 737 MAX software update certified. A test flight before a certification flight has been conducted, too.

That said, airlines in the United States have all recently extended the Boeing 737 MAX grounding - a move that will negatively impact their revenues, especially since we are diving into the busy summer travel season.

As of right now, American Airlines has decided to ground its 24 Boeing 737 MAX 8 planes through August 19; United Airlines is grounding its fleet of 14 Boeing 737 MAX 9 aircraft through early July; and Southwest Airlines is grounding all 34 Boeing 737 MAX 8 jets through August 5.

American Airlines, United Airlines and Southwest Airlines are all working to re-accommodate affected customers' flight plans.

While the CEO of American Airlines Group, Doug Parker, is confident that the 737 MAX aircraft will be recertified to fly before August 19 rolls round, the world's biggest airline is going forward with its decision to ground its MAX jets in a bid to plan more reliably for the peak travel season. Also, American Airlines wants to minimize disruption to its customers' travel plans as much as possible. Around 115 flights will be canceled daily through August 19 - the 115 flights make up roughly 1.5% of American Airlines' total flying each day in summer 2019.

Up until now, United Airlines has been using spare aircraft to operate flights to get where their customers are going. The Chicago-based carrier acknowledges that it is going to be more challenging especially during the peak of the busy summer travel season.

United Airlines does not operate the MAX 8 aircraft - the same plane model involved in the Lion Air and Ethiopian Airlines tragedies. Despite the worldwide grounding of the MAX aircraft, United Airlines executives are still expecting new MAX planes to be delivered this year.

It is not known how many flights will be canceled each day until United Airlines' MAX 9 aircraft go back into service. Southwest Airlines - the carrier with the most number of MAX planes grounded in the United States - has not confirmed the number of flights it will be canceling each day as well due to prolonged grounding of its 34 MAX 8 planes.

Denise Bay is a staff writer at GET.com. Email: denise.bay@get.com.