A top Boeing executive has apologized for the problems highlighted by the mid-flight blowout of a door plug on an Alaska Airlines flight and vowed to regain the trust of customers and regulators. The comments from Stan Deal, CEO of Boeing’s commercial plane unit came Friday, just as Alaska began returning its 737 MAX 9 planes to service, weeks after the mid-air emergency focused intense scrutiny on the huge aviation firm. “Our long-term focus is on improving our quality so that we can regain the confidence of our customers, our regulator and the flying public,” Deal wrote in a note to staff. “Frankly, we have disappointed and let them down. We are deeply sorry for the significant disruption and frustration for our customers. He added: “We have to deliver perfect airplanes each and every time.” In the weeks since the incident, Deal said several steps had been taken “to strengthen quality assurance and controls.” They included adding new levels of quality checks and appointing a retired navy admiral, Kirkland Donald, to oversee an independent review of Boeing’s safety and quality practices. This week, 10,000 Boeing employees working on 737 MAX production paused their work for a day to discuss ways of improving safety practices, “a quality stand-down at a scale we have not done before,” according to Deal. Deal added that following Alaska, United Airlines, Aeromexico and Turkish Airlines are also set to return their 737 MAX 9’s to service “in the coming days.” The US Federal Aviation Administration grounded 171 MAX 9 planes after the January 5 incident, in which a door plug blew out mid-flight. While nobody was seriously injured, inspectors have said the episode could have been catastrophic. The US Transportation Safety Board (NTSB) has been investigating the incident and is expected to report on its findings next week.