A Frontier Airlines Airbus A321-200, registration N712FR performing flight F9-751 from Denver,CO to Phoenix,AZ (USA) with 211 people on board, was climbing out of Denver's runway 25 when the crew stopped the climb at 10,000 feet reporting an electrical odour in the cockpit. The aircraft returned to Denver for a safe landing on runway 34R about 15 minutes after departure and taxied to the apron. Emergency services boarding the aircraft confirmed a noticeable electrical odour. There were no injuries, the passengers disembarked normally.

A replacement A321-200 registration N704FR reached Phoenix with a delay of about 3 hours.

https://flightaware.com/live/flight/FFT751/history/20210311/1636Z/KDEN/KPHX