Call it the trust factor. It’s what helped three in-house lawyers earn major promotions this month at their companies, while the troubled legal department at General Motors Co. went outside for its new general counsel and two top deputies.

In the biggest act of trust, United Airlines Holdings Inc. last week put the company in the hands of general counsel Brett Hart after its new CEO had a heart attack and went on medical leave. As acting CEO, Hart becomes the first African-American to head a major airline.