That program rewards all eligible employees with up to $125 each month for on-time departures, on-time arrivals and other performance-related measures.

“The employee group that would have been eligible for those bonuses was much larger” than that of the lottery system, Taylor Garland, spokeswoman for the Association of Flight Attendants, said in a phone interview. The bonuses were given to not only United’s 24,000 flight attendants but also its pilots and gate agents among others, she said.

Under the lottery system, just 1,361 employees would receive bonuses, according to the United Airlines memo, and only one would be chosen for the top cash prize of $100,000.

Other prizes included the Mercedes sedans (10 winners), a choice between a vacation package or $20,000 (20 winners), a similar choice at the $10,000 level (30 winners) and a variety of other cash prizes. The bonus that employees had the best chance of winning was $2,000 cash, which would have been given to 1,000 workers.

In February, Mr. Kirby lauded the company for finishing first among its competitors for on-time departures, “marking the seventh time in the past 10 months that we’ve ranked in the top spot for mainline departures.”

Paying out bonuses to both rank-and-file workers and executives costs the company tens of millions of dollars every year.

According to United’s latest earnings report, employees earned approximately $30 million in incentive payments for achieving operations performance goals in the fourth quarter ending in December, and approximately $87 million in earned bonuses in 2017. The report did not break out bonuses for executives and other workers.