I don't know the precise details of the covenant breach (other than that there was one) but it must have been a serious breach to trigger a requirement to repay the debt.
Less serious covenant breaches tend to result in less onerous penalties, such as a block on dividends until a year or so after the breach is remedied. Only serious breaches result in the lender being able to demand immediate repayment, which is the case here.
Of course most lenders are reluctant to implement a demand for immediate repayment, as this could result in them owning the asset, when they are in no practical position to manage it. Hence the 'standstill agreement' at LPL, where the lender gave the airport company time to sort itself out before calling in the loan. In this case, with Vantage being in no position to put in more money, this appears to have led to Peel taking the shares back from Vantage, who were in no position to put up much of a fight. Now that Peel are sole owners again I would expect them to settle with the banks, given Peel's deep pockets. Probably this will involve Peel repaying at least part of the outstanding loan.
Meanwhile the airport carries on operating quite happily.