The tensions over Mr. Dickson’s nomination are an unwelcome distraction for the F.A.A. The agency is under fire for its role in certifying the Boeing 737 Max and then being too slow to ground it after a second crash involving the jet in March. It is now devoting significant resources to getting the Max, which has been grounded since March, flying again. It is also working to enact many new regulations included in the F.A.A. Reauthorization Bill passed last year.

[Boeing’s Dreamliner plant is said to face a federal inquiry.]

Senate Democrats are concerned about Mr. Dickson’s role in a case involving the Delta pilot Karlene Petitt, which was first reported by CNN. In 2016, Ms. Petitt presented Mr. Dickson and other executives with a report that she said documented unsafe conditions, including inadequate training and overworked pilots. Instead of taking her concerns seriously, Ms. Petitt said that the company retaliated against her.

In a complaint to the Occupational Safety and Health Administration, Ms. Petitt alleged that soon after she raised her safety concerns, she was interviewed by a Delta investigator. Based on feedback from that investigator, Delta decided to have Ms. Petitt examined by a psychiatrist. The psychiatrist diagnosed a bipolar disorder, leading her to be banned from flying for more than a year.

Two subsequent evaluations by other psychiatrists reversed that diagnosis, and Ms. Petitt was cleared to fly again. The F.A.A. conducted an investigation of Ms. Petitt’s safety complaints and substantiated some violations by Delta. Ms. Petitt is seeking damages in excess of $1 million, and her claim is pending before an administrative law judge at the Labor Department.

Though Mr. Dickson was involved in Ms. Petitt’s case and sat for an extended deposition, he did not mention the case in responses to a questionnaire he submitted as part of his application to be the F.A.A. administrator. The questionnaire asked if he or any company he was involved with was a named party in a lawsuit. Mr. Dickson noted that Delta was involved in many legal proceedings, but did not mention the Petitt case.