Amid a string of high-profile incidents since the start of the year, both Boeing  (BA)  and United Airlines  (UAL)  have been under the microscope when it comes to all things airline safety.

Most recently, a Boeing 737-800 carrying 139 passengers from San Francisco to Oregon lost an external panel in the air on March 15 (it was already close to its destination and was able to land safely.) A few weeks earlier in February, a passenger-filmed video of a shredded United plane wing flapping in the wind went viral on the internet.

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While the biggest scrutiny is on the manufacturer that supplies United with its planes (Boeing is currently facing a DOJ criminal investigation over an Alaska Airlines  (ALK)  plane with the blown-out door panel), United CEO Scott Kirby also addressed the recent incidents in a memo sent to customers and shareholders.

Safety incidents have 'sharpened our focus,' United Airlines CEO says

"Unfortunately, in the past few weeks, our airline has experienced a number of incidents that are reminders of the importance of safety," Kirby wrote. "While they are all unrelated, I want you to know that these incidents have our attention and have sharpened our focus."

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Other incidents that have caused United travelers to question the airline include a United Boeing 737-900ER whose engine caught flames after taking off from Houston and a Boeing 777 that lost a wheel while taking off from San Francisco, both in the last month.

While the Chicago-based carrier flies a range of Boeing,  Airbus  (EADSF)  and Embraer  (ERJ)  jets, it is presently Boeing's largest customer and is currently in talks over whether it should change its order to more 737 Max 9 or the yet-to-be-certified Max 10 that it had hoped to start receiving in coming years.

United Airlines: 'Reviewing the details of each case'

Kirby further said that it 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."

This will manifest itself as an extra day of training for United pilots in May and reworking the training curriculum for newly-hired maintenance technicians to be more centralized.