William Kirby, a professor at Harvard Business School, has been closely following Chinese conglomerate HNA Group Co for more than 10 years. After watching HNA blossom from a regionally based airline into a ranking on the Fortune 500 list, Kirby said the company has learned how to manage its far-flung assets in part from its experience in China.

"While China may seem like it is one country or one market, any company that becomes big in China must manage multiple cultures in multiple places," Kirby said in an interview on Monday. "HNA has developed a coherent corporate culture in China that has served them well."

Kirby wrote case studies of HNA Group in 2008 and 2016. His recently-published 2018 study, "HNA Group: Global Excellence with Chinese Characteristics (B)," describes HNA Group's history as an aviation company and outlines its philanthropic philosophy, commitment to innovation and strategic business model.

HNA Chairman Chen Feng discussed HNA's development at the Harvard Business School on Monday, along with the 2018 study. "I am honored to speak with future business leaders about HNA Group's global presence and growth," Chen said in a statement.

Kirby said HNA not only expanded in China, but also on a global scale with operations in aviation, finance, logistics, real estate and tourism.

"Here in Boston we never had any nonstop airline service between Boston and China until HNA inaugurated nonstop service several years ago," said Kirby.

Today, HNA produces more than $90 billion in revenue yearly and manages an international work force of more than 400,000. "HNA is focused on trying to not disrupt the corporate culture in the existing companies it has acquired," Kirby said.

Kirby said HNA's business model emphasizes philanthropy. "That has been a central part of the company's public and private standing," he said and more than half of the privately held company (52 percent) is controlled by charitable foundations in China and the US.

HNA has been involved in some high-profile acquisitions. In 2016, the company paid $6.5 billion to buy a 25 percent stake in Hilton Worldwide Holdings Inc from Blackstone Group LP. Recently HNA slightly reduced its stake in Germany's Deutsche Bank AG to 9.2 percent of voting rights from 9.9 percent previously.

Last week, Bloomberg reported that HNA was shopping several US buildings valued at about $4 billion to reduce debt.

"HNA was encouraged to become a global company with strong encouragement from the Chinese banking sector," said Kirby. "One thing that no one can predict is how policies can change in China."

Chen told Reuters last month that the company's liquidity problem exists "because we made a big number of mergers", even as the external environment became more challenging and China's economy "transitioned from rapid to moderate growth", impacting the group's access to new financing.

"I think the challenge for HNA and other companies in China is what do you do when the spigot is turned off," Kirby said.

"HNA now has to adjust to a world in which Chinese policy clearly has changed."