Boeing 737 Max 8 passenger planes sit on the tarmac at Phoenix Sky Harbor International Airport on March 13, 2019 in Phoenix, United States. Ralph Freso | Getty Images

After two deadly crashes, Boeing is scrambling to persuade regulators to allow its cash cow, the 737 Max, back in the air. Rebuilding trust with the public will be even trickier. Aviation authorities worldwide in mid-March grounded Boeing's best-selling jet, a revamped and more fuel-efficient version of its workhorse aircraft that has been flying for more than 50 years. The model crashed in Indonesia in October and Ethiopia less than five months later, claiming 346 lives combined. The aerospace giant now has to repair relationships with travelers, some of whom, surveys published Tuesday showed, would avoid the plane until it flies safely for half a year. It also has to mend things with airlines that have been left without the fuel-efficient jets during the peak summer travel season, and with flight crews who say they were blindsided by changes Boeing made to the new planes before the company delivered them to airlines. Boeing is under fire from lawmakers, and multiple investigations are looking at how U.S. regulators came to certify the plane just over two years ago.

Too slow

Communications experts say Boeing was too slow to apologize and provide information to a nervous public, missteps now recognized by the company's CEO. "We know that our communication in some cases was not as effective, or not as complete as it should have been, and there are areas where we'll improve transparency," CEO Dennis Muilenburg told CNBC in an interview Monday. "We know we have work to do." In the wake of the crisis, the public isn't necessarily looking for an immediate apology, but instead want detailed information about how the company is going to get to the bottom of the issue, said Dan Hill, a crisis communications consultant whose past clients have included aerospace manufacturers and airlines. "They don't want stiff, rigid" statements, he said. "They were missing a bit of that empathetic voice." Another of Boeing's mistakes was that it acted as a business-to-business company, providing information to airlines but not enough to the public, said Gene Grabowski, a partner at K Global, a public relations firm that helps companies navigate crises.

"B-to-B is dead," he said. "They forgot in a crisis, they're a [business to consumer] company." Ed Bastian, CEO of Delta, which does not fly the Max but is a longtime Boeing customer, said the manufacturer "didn't get out far enough in advance of the story. "The story was told about them rather than being able to manage the story, Bastian said.

Convincing crews

An automated anti-stall system that Boeing installed on the planes has been implicated in the two 737 Max crashes. Known as MCAS, the system repeatedly pushes the nose of the plane down if the plane perceives it is in a stall. In the two crashes, pilots were battling the system after erroneous sensor data triggered it, sending the nearly brand-new jets into deadly plunges. Pilots said they didn't know about the system until after the first plane, Lion Air Flight 610, went down shortly after takeoff from Jakarta in October. In a tense meeting in late November, American Airlines pilots fumed over being kept in the dark about the system. "These guys didn't even know the damn system was on the airplane — nor did anybody else," said American Airlines pilot Michael Michaelis, according to a recording of the meeting obtained by CNBC. Pilots were given training on an iPad that lasted sometimes less than an hour to transition from flying older models of the 737 to the 737 Max.

Additional training

In addition to a software fix for the flight system, Boeing is preparing new training materials. Allied Pilots Association spokesman Dennis Tajer, an American Airlines 737 captain, said the training should be robust and that the union has asked the FAA to update flight handbooks. "You want us to be complaining" that the training is too long, he said. Flight attendants also need to be convinced. Boeing has recently met with unions representing flight attendants at United Airlines and Southwest Airlines, both of which operate the 737 Max. "If we're not safe, you're not safe," said Southwest Transport Workers Union spokesman Chad Kleibscheidel, who added that the union is continuing to speak with Boeing and that flight attendants will not be forced to fly on any aircraft they don't feel safe on.

Confidence questioned

Some want to hear from other Boeing employees. The Association of Flight Attendants, which represents United Airlines cabin crew requested a letter from Boeing engineers affirming whether they feel confidence in the software fix, a spokeswoman for the union said. "The traveling public looks to flight attendants for reassurance whenever there is any irregularity in air travel," said Sara Nelson, president of the union. "The process for implementing the fix and FAA certification must be transparent and conservative in order to restore confidence. We do very much want Boeing and the FAA to get this right so that we can advise crews and passengers that we are safe to fly. We're not there yet." Flight attendants were among the groups that called for the 737 Max to be grounded before the FAA pulled the trigger on March 13, following dozens of their counterparts worldwide, a departure from how the FAA and international regulators have operated for decades. The worldwide grounding of the 737 Max is a blow to airlines, the customers that helped propel Boeing to $100 billion in sales last year. Airlines that have added the 737 Max to their fleets over the past two years have had canceled thousands of flights during the peak summer travel season, when airline revenue is generally the highest of the year, denting revenues at some of the largest airlines. The three U.S. airlines with the Max in their flights removed the plane from their schedules through August. "I think there will be recompense of some sort over time," said United CEO Oscar Munoz told CNBC last week. American Airlines has made similar statements. "I don't want my airline suffering from Boeing's failings," said Tajer.

Skittish travelers

Passengers will have to be convinced as well. A UBS survey published on Tuesday found that 70% of flyers polled would hesitate to book on the Max. A fifth of respondents said they'd wait for the 737 Max to fly safely for six months before booking a flight on the jet. A separate survey by travel consulting firm Atmosphere Research Group said at least 40 percent of the people it polled said they would book more expensive or longer-connecting flights to avoid the plane. Airlines including Southwest and United said they won't charge passengers to change their flights if they are skittish about traveling on the Max. American doesn't have a rebooking policy for the Max but "we will always work to ensure we have policies and procedures in place that take care of our customers and team members," said spokesman Ross Feinstein. Even if passengers do switch off of a 737 Max, airlines frequently swap aircraft due to weather, mechanical and other issues, so there is a chance, even very slight, that the Max may be used last-minute. "Usually the public doesn't care what aircraft they're on," said Kevin Michaels, managing director of AeroDynamic Advisory, an aviation consulting firm. "Now they do." Blanket bans on aircraft are unusual but have occurred. In January 2013, battery fires on new Boeing 787 Dreamliners prompted the agency to ground the planes that month. In 1979, the FAA grounded McDonnell Douglas DC-10 planes after deadly crashes. But there is a key change this time, Michaels said: social media. Passengers took to Twitter to try to get their flights changed and pressure Boeing to ground the planes before the FAA ordered them out of service. "Historically, it's been about the manufacturer, the airline and the regulator working through this," Michaels said, adding that the bar for the reintroduction of the plane is very higher. "It needs to have a flawless introduction," he said. United and Southwest executives said they wouldn't force travelers to fly on the 737 Max and would waive change fees and fare differences so they can switch to another aircraft. "The first and foremost objective from our perspective is not to assume that everyone will want to fly [the 737 Max], or assume everyone will get over it," he said.