Activist investor Elliott Investment Management has taken a more than $5 billion stake in Honeywell International and is calling for the conglomerate to split into two separate companies.

In a letter sent to Honeywell's board, Elliott said that the Charlotte, North Carolina-based company needs to simplify its structure as it deals with uneven execution, inconsistent financial results and an underperforming stock price.

Elliott is advising Honeywell to separate its automation and aerospace businesses.

"As independent entities, Honeywell Aerospace and Honeywell Automation would benefit from simplified strategies, focused management, improved capital allocation, better operational performance, enhanced oversight, and numerous other benefits now enjoyed by dozens of large businesses that have moved on from the conglomerate structure, including former conglomerates General Electric, United Technologies, and many more," Elliott wrote.

The activist investor believes splitting up the aerospace and automation businesses would result in share-price gains of 51% to 75% over the next two years.

"Honeywell's board of directors and management acknowledge and appreciate the perspectives of all our shareholders," Stacey Jones, Chief Communicator at Honeywell, said in a statement. "Although Elliott had not made us aware of their views prior to today, we look forward to engaging with the firm to obtain their input. Our leadership welcomes investor feedback as we continue to execute a disciplined strategy, which includes pursuing sustainable growth, optimizing the portfolio, and maintaining an accretive capital deployment program."

Shares of Honeywell rose 5% in early trading Tuesday.