Bristow Group has warned that it may "not be successful in complying with the covenants contained in our debt instruments and lease agreements".

In a stock market filing, the firm said it had entered into waiver letters with its secured equipment financing lenders waiving "certain events of default (...) until June 19, 2019, subject to the delivery of the December 31, 2018 financial statements by such date and certain other conditions". The waivers allow Bristow to defer interest payments on secured and convertible notes due in 2023.

Bristow also said that it has engaged financial and legal advisors to assist it in, among other things, analyzing various strategic financial alternatives to address our liquidity and capital structure, including strategic financial alternatives to restructure our indebtedness.

"We and certain of our subsidiaries may elect to implement such a transaction through Chapter 11 of the United States Bankruptcy Code ('Chapter 11') in order to obtain court approval of such transactions and to facilitate the stakeholder approvals necessary to implement such transactions," it said.

The group's FY2018 financial statements, that have not yet been published, may also contain disclosures that would "express substantial doubt" about its ability to continue as a going concern.

Bristow operates helicopter, search and rescue, and aircraft support services in the US, North Sea, Nigeria, Australia, Brazil, Canada, Russia and Trinidad. It also owns Airnorth (Australia) (TL, Alice Springs), 60% in Eastern Airways (T3, Humberside), 41.9% in Líder Aviação (Belo Horizonte Pampulha), 40% Cougar Helicopters (Canada) (CHI, St. John's), and 25% in Petroleum Air Services (UF, Cairo Int'l).