As of 2015, the best way to file a complaint with Frontier Airlines is to click Contact Us at the foot of the airline's webpage, scroll down to Customer Relations, click Feedback and Concerns, and complete the online form with details of your complaint. Alternatively, write a letter of complaint addressed to the attention of Customer Relations at Frontier Airlines, PO Box 492085, Denver, Colorado 80249, or call 801-401-9000 and say "other options" followed by "feedback and concerns."
To complete the Frontier Airlines contact form, enter an email address and a suitable subject, and select Feedback or Concerns from the categories listed in the drop-down menu. Enter flight details - including number, date, departure city and confirmation code - and details of the complaint in the comments box, using no more than 800 characters. You must complete all boxes marked with a red asterisk before submitting the form. If you choose to contact the airline in writing or by telephone, make sure you include the flight information in your written complaint, and have the details at hand when making your call.
Scroll to the bottom of Frontier Airline's home page, and click Customer Service Plan under Customer Service to read the airline's commitment to its customers. The airline undertakes to acknowledge receipt of written complaints within 30 days and promises to reply in more detail within another 30 days.