Two sensors, both at bottom, that measures the angle of attack is pictured on a Boeing 737 MAX 8 airplane outside the company’s factory on March 22, 2019 in Renton, Washington.Stephen Brashear | Getty ImagesFederal safety investigators on Thursday said Boeing overestimated how well pilots could handle to a flurry of alerts when things go wrong on its 737 Max planes, which have been grounded since March after two fatal crashes killed a total of 346 people.The National Transportation Safety Board released a series of recommendations for aircraft safety assessments, including factoring in human responses when things go awry, the first formal guidelines since the crashes.A flight-control system designed to prevent the planes from stalling misfired on both crashed flights: an Lion Air 737 Max in Indonesia last October and an Ethiopian Airlines plane of the same type in March.”Multiple alerts and indications can increase pilots’ workload, and the combination of the alerts and indications did not trigger the accident pilots” to steady the plane, the NTSB said. The pilots’ actions “did not match the assumptions of pilot responses” to a misfire of the flight-control system.Boeing based its safety assessment of the planes, which the Federal Aviation Administration approved, on those fast response times, the NTSB says.Boeing and the FAA are facing several investigations into the design and certification of the jets, Boeing’s best-selling aircraft ever.”Safety is a core value for everyone at Boeing and the safety of our airplanes, our customers’ passengers and crews is always our top priority,” Boeing said in a statement. “We value the role of the NTSB in promoting aviation safety. We are committed to working with the FAA in reviewing the NTSB recommendations.”The FAA said it welcomed the NTSB’s recommendations.”The agency will carefully review these and all other recommendations as we continue our review of the proposed changes to the Boeing 737 MAX. The FAA is committed to a philosophy of continuous improvement,” it said in a statement. “The lessons learned from the investigations into the tragic accidents of Lion Air Flight 610 and Ethiopian Airlines Flight 302 will be a springboard to an even greater level of safety.”Boeing has said it expects to submit its software fix and new pilot training materials to FAA in the coming weeks, in an effort to get the planes flying again, which it expects to do early in the fourth quarter.The FAA has said several times that it has no set timeline for allowing the planes to fly again.Boeing shares were little changed in morning trading.