Exhibit 21 PHI, Inc. Subsidiaries of the Registrant at December 31, 2017 COMPANY PLACE OF ORGANIZATION / INCORPORATION % OF VOTING STOCK / MEMBERSHIP INTEREST OWNED Energy Risk, Ltd. Bermuda 100% HELEX, LLC Florida 100% PHI Tech Services, Inc. Louisiana 100% Helicopter Management, LLC Louisiana 100% Helicopter Leasing, LLC Louisiana 100% AM Equity Holdings, L.L.C. Louisiana 100% PHI Air Medical, L.L.C. Louisiana 100% MDHL, LLC Montana 100% Sky Leasing, LLC Montana 100% Vertilease, LLC Montana 100% Leasing Source, LLC Montana 100% PHI Century Limited Ghana 49% Personnel Outsourcing, Ltd. Cayman 49% PHI Air Europe Limited Cyprus 49% PHI Americas, Ltd. Trinidad 95.4% PHI-HNZ Australia Pty Ltd. Australia 100% Petroleum Helicopters Australia Pty Australia 100% HNZ New Zealand Ltd. New Zealand 100% HNZ Australia Holdings Pty Ltd. Australia 100% HNZ Australia Pty Ltd. Australia 100% HNZ Singapore Pte Ltd. Singapore 100% PHI NZ HoldCo Ltd. New Zealand 100% TAC Leasing, LLC Montana 100% VKA Leasing, LLC Montana 100% GJW Leasing, LLC Montana 100%