There are fresh questions about the financial health of the American private investment firm hoping to take over Everton after passenger planes belonging to an Australian airline it owns were repossessed and its carrier left on the brink of collapse.

777 Partners – which has loaned Everton more than £200m in the seven months it has been unsuccessfully attempting to convince the Premier League it has the funds to complete a proposed takeover of the Toffees – is in the grips of a new crisis in Australia, where an airline it wholly owns, Bonza, entered administration on Tuesday.

Related: Everton call in insolvency advisers amid fresh doubt over 777 takeover

Hundreds of passengers were stranded across Australia after low-cost airline Bonza abruptly cancelled all flights following the repossession of its four Boeing 737-Max 8 aircraft earlier that morning.

The development blindsided the airline’s CEO and the Miami-based 777 Partners, according to internal company communications seen by the Guardian.

777 Partners had part-owned Bonza’s fleet of aircraft, and routinely moved its 737s between the airline and Flair, a Canadian low-cost carrier it partly owns. However in April, AIP Capital – an investment manager that includes aviation assets such as aircraft and which had majority owned 777 Partners’ fleet of aircraft in a 51%-49% split – announced the formation of a new holding company to lease aircraft, Phoenix Aviation Capital.

Phoenix had announced “a definitive agreement to acquire the rights, interests and obligations of a portfolio of 30 737-8 aircraft from 777 Partners”. The repossessions were unexpected. “This was a surprise to both ourselves and 777 Partners,” Bonza’s CEO, Tim Jordan, said in a company memo on Tuesday.

The aircraft lease arrangements of the Miami-based investment firm were thrust into the spotlight in March last year when the four planes leased to Flair – three Boeing 737 Max 8s and one 737-800 – were repossessed due to outstanding fees, leading to operational issues.

The leasing contracts were terminated, with the repossession of the four aircraft on 10 March 2023 occurring after two default notices were issued to Flair on 16 and 22 February, according to particulars filed in the business and property courts of England and Wales in December.

777 Partners is now being chased for almost US$30m in unpaid aircraft leasing fees and damages related to the Flair repossessions. Separately, Flair has launched legal action against the lessors.

The Guardian contacted 777 Partners for comment.