Jet Airways defaulted on payments to a consortium of Indian banks on 31 December 2018.
In a disclosure on the Indian Stock Exchange, the cash-strapped airline says this was "due to temporary cashflow mismatch". However, it is not clear how much is outstanding.
Jet has been trying to implement liquidity initiatives, which themselves have been delayed.
They include seeking an equity infusion and a stake sale of its loyalty programme.
As of 30 September 2018, Jet had a gross debt of Rs 84.1 billion ($1.17 billion). Weak market conditions are also putting pressure on its yields and profitability.
The airline has also seen its long-term credit ratings gradually fall, with the latest ratings falling from B- to C in December last year.