Businessman Rakesh Gangwal has bought a substantial number of shares in Southwest according to SEC filings.

The documents, filed on October 2, show that around $100m of stock has been bought by the founder of IndiGo, who has since become a director of Southwest.

READ: Activist investor forces Southwest boardroom clear-out

The management of the airline has been under scrutiny in recent weeks as ‘activist investors’, notably equity firm Elliott have been directly critical of both leadership and policy at the low-cost carrier. This has resulted in a number of changes, such as a switch to allocated seating, and the replacement of half a dozen directors, including COO Gary Kelly.

These cuts are not deep enough for some investors, as Elliott has renewed calls for CEO Bob Jordan to step down.

However, Gangwal has been  on record as saying that he believes that the structural changes have gone far enough. In an interview with Reuters, he said “I believe changing the board structure and top leadership beyond what has been already announced, would be counterproductive and not in the best interest of shareholders.”

Southwest was once the model that other low-cost carriers based their business on. However, it has been criticised for not moving with the rest of the industry to take advantage of ancillary revenue streams.