Washington DC CNN  —  United Airlines is trying to reassure passengers after a series of incidents on its Boeing jets this year, sending out a statement to customers that safety is “at the center of everything that we do.” “While they are all unrelated, I want you to know that these incidents have our attention and have sharpened our focus,” United CEO Scott Kirby said in a Monday morning message to customers. On Friday in a United Boeing 737-800 landed in Medford, Oregon, with a panel from the underside of the fuselage missing. Earlier this month, United suffered a series of four incidents, all involving Boeing jets . A United Boeing 737-900ER spewed flames from an engine after takeoff from Fort Meyers, Florida, a United Boeing 777 lost a wheel during takeoff from San Francisco, a United Boeing 737 Max slid off a runway in Houston, and a United Boeing 777 trailed hydraulic fluid leaving Sydney. “Our team is reviewing the details of each case to understand what happened and using those insights to inform our safety training and procedures across all employee groups,” Kirby said. United is adding an extra day to pilot training, retooling training for new mechanics, and “dedicating more resources to supplier network management.” Passengers seeing a series of bad headlines about the airline and its Boeing jets may consider booking away from the airline. United, in its letter, is trying to prevent customers from leaving. Beyond the problems on United flights, the most dramatic Boeing incident this year involved an Alaska Airlines Boeing 737 Max 9 that lost a door plug in a January 5 flight, leaving a gaping hole in the side of the plane. And last week a Latam Airlines flight from Sydney, Australia to Auckland, New Zealand plunged suddenly, causing some passengers to be thrown to the ceiling of the cabin. Investigators are still looking at the causes of both those incidents, but a preliminary report from the National Transportation Safety Board found Boeing left the bolts off the 10-week-old Alaska Air jet needed to keep the door plug in place. And Boeing suggested the Latam incident may have been caused by an incident in the cockpit and not anything to do with the plane’s controls. The age of the aircraft in the United incidents suggest that the cause could lie with United personnel, rather than Boeing’s well documented quality issues. Still, United’s operations have been disrupted by Boeing’s problems. It has frozen hiring for a new class of pilots, because it won’t be getting as many new planes from Boeing this year as originally promised after production was slowed by the FAA. And its fleet of 737 Max 9 jets were grounded for three weeks in January following the incident at Alaska Air. In addition, certification of a new model of Boeing jet that United has ordered, the 737 Max 10, has also been put on hold but the quality and safety problems at the company. Kirby told investors last week that United is looking at possibly buying more jets from Boeing competitor Airbus, and he said earlier this year that the Alaska Air incident was the “straw that broke the camel’s back” on its plans to get deliveries of the Max 10 any time in the foreseeable future.