Delta Air Lines Inc. customers aren’t the only ones unhappy about the thousands of flights the carrier has canceled since Friday. Its pilots are, too. 

Darren Hartmann, chairman of the Air Line Pilots Association at Delta, blasted the situation in a letter to members of the union on Tuesday, lamenting the “inability to contact the company in any capacity and the feeling that we have been abandoned in the system” during the disruptions.

The US Transportation Department launched an investigation of Delta’s treatment of passengers during its recovery from a technology glitch last week that forced the carrier to cancel more than 5,000 flights, with more disruptions possible this week. Pilots and crews have been particularly affected as the airline works to fully recover a flight management system that links those personnel to aircraft across the airline’s system.

“I share your frustration in seeing passengers stranded while we, as crew members, experience the same unacceptable obstacles we face during every” disruption of the airline’s normal operations, Hartmann said in the letter. The union represents about 15,000 Delta pilots.

Delta is doubling normal pay for pilots who pick up extra trips through Friday, and using some aviators to operate the flights they’re booked on to get to their next assignments if they are qualified and rested, Hartmann said in the letter. The union stressed that pilots “above all else” should make sure they get adequate rest.