The U.S. trustee overseeing the bankruptcy proceedings for American Airlines' parent company is questioning a $19.9-million severance package for the company's top executive.

In a filing made last week, Trustee Tracy Hope Davis said the airline, which filed for bankruptcy in 2011, is obligated to explain the severance package it proposes for its Chief Executive Tom Horton.

AMR plans to merge with US Airways Group, the parent company of US Airways, to form what is expected to be the nation's largest airline.