PHI Inc. was facing a deadline to pay back $500 million in unsecured notes. The helicopter company didn’t have the money. So instead, the Louisiana-based firm declared bankruptcy late March 14, just minutes before the day the payment came due.

The Louisiana-headquartered firm, which operates over 240 aircraft, is the latest helicopter company to declare bankruptcy amid heavy debt loads and declining demand for their services from offshore oil drillers. PHI employs about 2,200 workers in over 70 locations around the world.

A number of other helicopter companies have faced financial difficulties including bankruptcy. Waypoint Leasing Holdings Ltd., an Irish...