Typically, the A-notes are broken down into smaller pari passu notes and put into different CMBS. For instance, a $20 million CBMS loan could be divided into three $5 million pari passu A-notes, each of which is placed into a different CMBS and paid back on equal footing to the others. The other $5 million goes into a B-note, which is subordinate (non-pari passu) and pays out only after the A-notes are satisfied.
While the A-notes may vary in size, they all have the same payment priority because they're pari passu. So all A-note holders are treated equally and without preference. Meanwhile, the B-notes remain subordinate and don't partake in the pari passu treatment.
Benefits of pari passu
Pari passu clauses have become an essential part of commercial real estate. In real estate partnerships, they provide an equitable way to distribute profits. In the world of commercial mortgage-backed securities, they are an effective way to improve liquidity.
Aside from putting a group of investors on equal footing (the A-note holders), the pari passu structure offers a way to split up big loans into smaller CMBS that are more attractive (and less risky) to investors. That helps lenders bundle and sell loans, which improves their cash flow and capital position -- which means the lenders can make more loans. And that allows real estate developers to fund and pursue more commercial real estate projects.