structuring-abs-transactions

# Structuring Abs Transactions

Designs asset-backed securitization structures with tranche hierarchy, credit enhancement, and cash flow allocation mechanics.

## When To Use

- Designing a new ABS issuance and defining the capital structure (tranche count, sizing, and subordination levels)
- Evaluating credit enhancement adequacy for a given collateral pool and target ratings
- Building or reviewing a cash flow waterfall for principal and interest allocation across tranches
- Comparing structural alternatives (sequential pay vs. pro rata, turbo features, reserve account sizing)
- Stress-testing an existing structure against collateral performance scenarios (default, prepayment, recovery)

## Inputs To Gather

- **Collateral pool data**: Asset type (auto loans, credit cards, trade receivables, RMBS, CLO), aggregate balance, weighted-average coupon, WAL, seasoning, geographic/obligor concentration
- **Historical performance**: Default rates, loss severity, prepayment speeds (CPR/ABS), delinquency migration curves, recovery timing
- **Target capital structure**: Number of tranches, target ratings per tranche (AAA through equity/residual), desired advance rate
- **Credit enhancement parameters**: Overcollateralization target, subordination levels, excess spread, reserve account initial deposit and floor, any third-party support (surety wrap, LOC) [VERIFY against current rating agency criteria]
- **Waterfall rules**: Payment priority (sequential vs. pro rata), interest-first vs. principal-first, trigger events (delinquency, cumulative loss, OC tests), turbo/catch-up mechanics
- **Deal economics**: Pricing assumptions per tranche, servicing fee, trustee fee, swap costs (if applicable), target equity yield
- **Regulatory context**: Risk retention requirements (5% vertical/horizontal/L-shaped), Reg AB II disclosure obligations, EU securitization regulation (STS eligibility if cross-border) [VERIFY jurisdiction-specific rules]

## Workflow

1. **Profile the collateral pool**
   - Stratify by key risk dimensions (FICO/credit score, LTV, loan age, geography, obligor size)
   - Compute pool-level statistics: WAC, WAM, WAL, concentration limits
   - Identify data gaps or quality flags that affect structural assumptions

2. **Set base-case and stress scenarios**
   - Define base-case default curve, prepayment speed, and recovery assumptions from historical analogs
   - Layer rating-agency stress multiples for each target tranche rating (e.g., Moody's Aaa stress = ~3.5x base loss for consumer ABS) [VERIFY current agency multiples]
   - Include prepayment stress (fast/slow) and recovery lag stress

3. **Design the tranche hierarchy**
   - Size senior tranche to survive the highest stress scenario with full principal recovery
   - Size mezzanine tranches to meet intermediate rating targets with required coverage
   - Residual/equity tranche absorbs first loss — size as the remaining balance after credit enhancement allocation
   - Confirm subordination percentages align with precedent transactions and rating agency expectations

4. **Build the cash flow waterfall**
   - Map interest waterfall: servicing fee → trustee/admin fees → senior interest → mezzanine interest (by seniority) → reserve account replenishment → excess spread to equity (or turbo principal)
   - Map principal waterfall: sequential (senior first) until triggers are met, then potentially pro rata; define trigger reversion mechanics
   - Model OC and IC trigger tests at each payment date — specify consequences of trigger breach (diversion of cash flow, trapping excess spread, acceleration of senior principal)

5. **Size credit enhancement**
   - Overcollateralization: target and floor OC as percentage of pool balance
   - Reserve account: initial deposit (typically 0.5%–2.0% of initial pool), floor amount, release conditions
   - Excess spread: compute available excess spread under base and stress; determine if spread capture or turbo principal is needed
   - Validate total credit enhancement (subordination + OC + reserve + excess spread) against rating agency required levels

6. **Run scenario analysis**
   - Execute cash flow model under base, upside, and multiple downside scenarios
   - Track key outputs per tranche: WAL, yield, principal window, break-even default rate, loss coverage ratio
   - Identify the scenario at which each tranche experiences a principal shortfall (break-even analysis)
   - Sensitivity analysis on key variables: default timing (front-loaded vs. back-loaded), recovery rate, prepayment speed

7. **Document the structure**
   - Produce a structural summary with tranche table, waterfall diagram, and credit enhancement summary
   - Highlight structural risks: concentration risk, commingling risk, servicer disruption, basis risk (fixed/floating mismatch)
   - Note any deviations from market-standard terms and rationale

## Output

- **Tranche table**: For each tranche — class name, rating, initial balance, percentage of deal, coupon type/rate, expected WAL, subordination level, payment window
- **Waterfall diagram**: Visual or tabular representation of interest and principal payment priority, trigger tests, and cash flow redirection logic
- **Credit enhancement summary**: Breakdown of total CE by component (subordination, OC, reserve, excess spread) with comparison to rating agency required levels
- **Scenario results matrix**: Tranche-level performance metrics (principal loss, WAL, yield) across base and stress scenarios
- **Risk flags**: Structural features that create tail risk, trigger volatility, or rating migration sensitivity
- **Recommendation**: Optimal structure with rationale, or comparison of 2–3 structural alternatives with trade-offs (advance rate vs. execution certainty, equity yield vs. rating stability)

## Quality Checks

- Subordination levels for each tranche meet or exceed rating agency published benchmarks [VERIFY against current Moody's/S&P/Fitch/KBRA criteria for the specific asset class]
- Cash flow waterfall is internally consistent — all cash is allocated (no leakage), and priority of payments matches legal documentation intent
- OC and IC triggers are correctly modeled with breach-and-cure logic
- Stress scenarios cover both severity (high default) and timing (front-loaded loss) dimensions
- Risk retention slice (horizontal, vertical, or L-shaped) is correctly sized at minimum 5% of total issuance [VERIFY applicable jurisdiction — US Dodd-Frank vs. EU/UK rules]
- Excess spread calculations account for servicing fees, swap costs, and trustee fees before measuring available CE
- Break-even analysis confirms each rated tranche survives its corresponding rating stress with zero principal loss
- All collateral pool statistics reconcile to the actual tape (no stale or placeholder data)