WASHINGTON (Reuters) - It would cost $1.8 billion and take 10,000 new employees for the U.S. aviation regulator to handle all aircraft certification internally, the agency’s acting chief told a Senate panel on Wednesday, facing tough questions after two Boeing 737 MAX crashes on how new planes are approved for flight.

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The Federal Aviation Administration delegates much of the work of airplane certification to manufacturers such as Boeing under a decades-old process. The FAA has agreed to significantly improve its oversight of organizations performing certifications on its behalf by July 2019, U.S. Transportation Department Inspector General Calvin Scovel told the panel.

The FAA’s acting head Daniel Elwell was asked why the FAA did not require disclosure of a new anti-stall software system in flight manuals or new pilot training before it certified the now grounded 737 MAX passenger jet in 2017.

Senator Ted Cruz, who chairs the Subcommittee on Science and Space, told Reuters after the hearing Elwell’s estimate was “a little bit of straw man” and deflected from serious concerns about the FAA delegation of responsibilities to Boeing.

Cruz said “there have been long standing concerns that have been raised about the closeness of the FAA with Boeing” and noted a 2012 audit that raised those questions.

“At this point we don’t know that’s what caused this, but on the face of it, it certainly seems inadequate - the pilot training material did not raise the details of this new system,” Cruz said.

Boeing said on Wednesday that it had reprogrammed software on its 737 MAX passenger jet to prevent erroneous data from triggering an anti-stall system that is under mounting scrutiny following the two deadly nose-down crashes.

The planemaker said the anti-stall system, which is believed to have repeatedly forced the nose lower in at least one of the accidents, in Indonesia last October, would only do so one time after sensing a problem, giving pilots more control.

Elwell also said that an alert to pilots that Boeing was making standard on all 737 MAX planes as part of a software upgrade was not “safety critical.” Boeing will stop charging for that alert and will not charge for another optional indicator.

“I find it hard to believe that a safety company like an airline would save a couple thousand dollars on an option that might improve safety,” Elwell said, who also defended the decision not to require new training after it was tested by pilots. “Fundamentally, the aircraft layout, the handling and the performance of the aircraft was the same.”

A group of 16 Democratic senators wrote Boeing on Wednesday raising “serious concerns” that Boeing charges extra for safety features like “backup fire extinguishers in the cargo hold and oxygen masks for flight crews” and some said they may introduce legislation to bar the practice.

In earlier comments on Wednesday, U.S. Transportation Secretary Elaine Chao asked why Boeing did not require safety features on its top-selling 737 MAX that might have prevented the crashes and said that would be “troubling.”

Shortly after Chao spoke, Boeing confirmed the company will make standard a safety feature on its 737 MAX that might have warned earlier of problems that possibly played a role in the crashes of Indonesian and Ethiopian planes that killed almost 350 people. It also said it would stop charging for another optional safety feature.

Senator Joe Manchin, a Democrat and pilot, questioned Chao why it took the FAA so long to ground the 737 MAX while regulators around the world moved faster to halt planes.

He also questioned why safety features were not mandated by Boeing or the FAA. “It looks like we are following,” Manchin said, adding it was “just wrong” not to require the alert.