The Joint Authorities Technical Review found the technology unprecedented: "If the FAA technical staff had been fully aware of the details of the MCAS function, the JATR team believes the agency likely would have required an issue paper for using the stabilizer in a way that it had not previously been used. MCAS used the stabilizer to change the column force feel, not trim the aircraft. This is a case of using the control surface in a new way that the regulations never accounted for and should have required an issue paper for further analysis by the FAA. If an issue paper had been required, the JATR team believes it likely would have identified the potential for the stabilizer to overpower the elevator." The MCAS has been under scrutiny following the fatal crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 soon after takeoff. The Boeing 737 MAX global fleet has been grounded by all airlines and operators, and a number of functional issues have been raised. The MCAS deflects the horizontal stabilizer four times farther than was stated in the initial safety analysis document. Due to the amount of trim the system applies to the horizontal stabilizer, aerodynamic forces resist pilot control effort to raise the nose. As long as the faulty AOA readings persist, a human pilot "can quickly become exhausted trying to pull the column back". In addition, switches for the horizontal stabilizer trim assist now serve a shared purpose of turning off the MCAS. In simulator sessions, pilots were stunned by the substantial effort needed to manually crank the trim wheel out of its nose down setting. Boeing CEO Dennis Muilenburg has stated that there was "no surprise, or gap, or unknown here or something that somehow slipped through a certification process." On April 29, 2019 he stated the design of the aircraft was not flawed and reiterated that it was designed per Boeing's standards. In a May 29 interview with CBS, Boeing admitted that it had botched the software implementation and lamented the poor communications. On September 26, the National Transportation Safety Board criticized Boeing’s inadequate testing of the 737 MAX, and pointed out that Boeing made erroneous assumptions on pilots’ response to alerts in 737 MAX, triggered by activation of MCAS due to a faulty signal from an angle-of-attack sensor. The Joint Authorities Technical Review (JATR), a team commissioned by the FAA for 737 MAX investigation, concluded that FAA failed to properly review MCAS. Boeing failed to provide adequate and updated technical information regarding the MCAS system to FAA during Boeing 737 Max certification process, and had not carried out a thorough verification by stress-testing of the MCAS system.