Library/CFA (Chartered Financial Analyst)/FIXED INCOME: CFA® Program Curriculum, 2026 • Level I • Volume 6/Learning Module 18 Asset-Backed Security (ABS) Instrument and Market Features

Learning Module 18 Asset-Backed Security (ABS) Instrument and Market Features

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Covered bonds and credit enhancement5 min
This chapter explains the instruments and market features of asset-backed securities (ABS). Covered bonds are senior debt issued by banks where eligible assets are ringfenced into a cover pool that remains on the issuer's balance sheet; investors have dual recourse (cover pool first, then unencumbered issuer assets). Covered bond structures include hard-bullet, soft-bullet, and conditional pass-through redemption regimes; they often include overcollateralization and LTV cutoffs to reduce investor risk. Covered bonds generally offer lower yields than comparable ABS because of dual recourse, strict eligibility, and dynamic pool monitoring.

Credit enhancement is critical in ABS structures. Internal enhancements include overcollateralization (collateral value exceeds issued debt), excess spread (difference between collateral coupon and ABS coupon retained to absorb losses), and subordination/credit tranching (creating senior and junior tranches so junior tranches absorb first losses). External enhancements include letters of credit, guarantees, and cash collateral accounts. The waterfall or priority-of-payments governs how cash flows and losses are allocated across tranches.

Key Points

  • Covered bonds remain on issuer balance sheet and provide dual recourse.
  • Redemption regimes: hard-bullet, soft-bullet, conditional pass-through.
  • Internal credit enhancements: overcollateralization, excess spread, subordination.
  • External enhancements include letters of credit and guarantees.
  • Waterfall dictates order of payments and loss absorption.
Non-mortgage ABS and securitization mechanics6 min
Non-mortgage ABS include structures backed by non-amortizing assets (for example, credit card receivables) and amortizing assets (auto loans, solar loans). Many credit card ABS feature a revolving or lockout period during which principal repayments are reinvested to replenish the collateral pool, followed by an amortization period when principal is distributed to noteholders. Early amortization (rapid amortization) provisions may trigger if replenishment fails or defaults worsen. Solar ABS and other whole-business or specialty ABS can include pre-funding or post-closing acquisition periods, and are typically supported by overcollateralization, subordinated tranches, reserve accounts, and excess spread to achieve investment-grade ratings.

Collateralized debt obligations (CDOs) issue securities backed by diversified pools of debt (loans, bonds, other CDOs). The dominant modern form is the collateralized loan obligation (CLO), backed by leveraged bank loans. CLOs are actively managed: a collateral manager buys and sells assets during a ramp-up and ongoing management period, subject to numerous tests and covenants (overcollateralization tests, concentration limits, rating triggers). CLO capital structures replicate a firm's capital structure with senior, mezzanine, and equity tranches. Equity tranche holders are residual claimants on excess cash flows and bear the most risk but can earn high returns if the manager outperforms. CLOs are subject to non-linear risks: manager skill, collateral default, structural tests that can redirect cash flows, and potential deleveraging if tests fail.

Key Points

  • Non-mortgage ABS often include revolving periods and reinvestment mechanics.
  • Rapid amortization protects investors when replenishment fails.
  • Solar and whole-business ABS use multiple credit enhancements for rating.
  • CDOs and CLOs are actively managed, with coverage and OC tests.
  • CLO equity tranches are residual and sensitive to manager performance.
RMBS, prepayment risk and CMOs6 min
MBS specifics: mortgage-backed securities (MBS) are bonds backed by residential or commercial mortgages. RMBS may be agency (government or GSE guaranteed) or non-agency (private label). Mortgage pass-through securities pass monthly principal, interest, and prepayments from the mortgage pool to investors net of servicing fees; weighted average coupon (WAC) and weighted average maturity (WAM) describe pool characteristics. Prepayment risk is central: contraction risk (prepayments accelerate when rates fall, shortening life) and extension risk (prepayments slow when rates rise, lengthening life). Time tranching (e.g., sequential-pay CMOs) redistributes prepayment risk across tranches by giving different tranches prioritized principal payments; other tranche types include Z-tranches (accrual), principal-only (PO), interest-only (IO), floating-rate, inverse floaters, PACs and support tranches. PAC tranches provide stable scheduled cash flows when prepayments remain inside a specified band; support tranches absorb variability.

Key Points

  • RMBS can be agency (guaranteed) or non-agency (private, enhanced).
  • Pass-throughs pass principal/interest/prepayments net of servicing fees.
  • Prepayment risk: contraction (shortening) and extension (lengthening).
  • Time tranching and CMOs allocate prepayment exposure across tranches.
  • Tranche types: Z, PO, IO, PAC, support, floaters, inverse floaters.
CMBS characteristics and risks5 min
Commercial MBS (CMBS) differ from RMBS: CMBS pools can be small and concentrated (even single-loan deals), making concentration risk and loan-level analysis important. Commercial loans are typically balloon loans (partial amortization with a large principal balloon at maturity), creating balloon risk (a form of extension risk) if borrowers cannot refinance or sell. CMBS commonly include call protection via loan-level lockouts, prepayment penalties, or defeasance, and structural protections (sequential tranching). Key underwriting metrics for CMBS are loan-to-value (LTV) and debt service coverage ratio (DSCR = NOI / debt service). CMBS often trade more like corporate bonds due to call protection and loan-level covenants. Understanding legal frameworks, jurisdictional foreclosure and insolvency rules, and structural features is essential for ABS investors.

Key Points

  • CMBS often have concentrated pools; single-loan deals heighten risk.
  • Commercial loans are usually balloon loans; balloon risk is extension risk.
  • Call protection: lockouts, prepayment penalties, defeasance mechanisms.
  • Key credit metrics: LTV and DSCR (NOI / debt service).
  • Legal/jurisdictional loan enforcement rules materially affect recoveries.

Questions

Question 1

Which redeeming feature of covered bonds postpones acceleration of payments until a later final maturity date, typically up to one year beyond the original date?

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Question 2

Which internal credit enhancement increases the collateral amount relative to the issued securities so losses can be absorbed before investors suffer principal loss?

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Question 3

During a credit card ABS's revolving period what typically happens to principal repayments from cardholders?

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Question 4

A CDO backed primarily by leveraged bank loans and actively managed with overcollateralization tests is commonly called what?

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Question 5

Which tranche typically absorbs initial losses in a securitization waterfall?

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Question 6

If a securitized pool has EUR1,200 million of collateral but issued EUR1,000 million of ABS, the ratio illustrating extra collateral is called what?

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Question 7

Which of the following is an external credit enhancement?

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Question 8

A mortgage pass-through security's coupon paid to investors equals the pooled mortgages weighted average coupon minus which type of fee?

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Question 9

Which tranche pays only interest from the pool and no principal and thus is especially sensitive to prepayment acceleration?

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Question 10

If mortgage prepayments accelerate because market rates fall, what risk is primarily realized by MBS investors?

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Question 11

Which legal structure is used to separate the collateral from the originator and isolate creditor claims in a securitization?

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Question 12

Which of the following best explains why some non-agency RMBS required credit enhancements prior to the global financial crisis?

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Question 13

A solar ABS backed by residential solar loans shows total collateral carrying value EUR144 million and ABS issuance value EUR54 million. The collateral multiple equals approximately:

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Question 14

Which of the following best describes a Planned Amortization Class (PAC) tranche?

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Question 15

Which metric equals property net operating income divided by annual debt service and is crucial for CMBS underwriting?

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Question 16

Which of the following increases when a mortgage loan's outstanding balance falls while property value rises?

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Question 17

A CLO manager fails an overcollateralization test. What structural consequence commonly occurs?

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Question 18

Which tranche in a sequential-pay CMO receives principal only after the prior tranche is fully repaid?

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Question 19

Which risk is most relevant to the investor in a principal-only (PO) tranche when interest rates fall?

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Question 20

Which of the following most reduces reinvestment risk for an investor in a securitization tranche?

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Question 21

Which structure is characterized by the issuer retaining the collateral on its balance sheet while ringfencing eligible loans into a cover pool?

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Question 22

Which feature is used in CMBS to permit prepayment only if the borrower acquires a government-securities portfolio replicating remaining cash flows?

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Question 23

Why do covered bonds generally yield less than otherwise similar ABS?

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Question 24

Which tranche would a pension fund with a long-term horizon likely choose in a sequential-pay CMO with tranches maturing in 5, 15, and 30 years seeking higher returns?

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Question 25

In a securitization waterfall example, total losses on collateral equal EUR70 million; junior tranche D is EUR25 million, tranche C EUR50 million, tranche B EUR100 million. Which tranche(s) are wiped out and which tranche shows partial loss?

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Question 26

Which statement is true about agency RMBS in the United States?

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Question 27

Which is a likely consequence if a CMBS loan reaches maturity and the borrower cannot refinance or sell the property to satisfy the balloon payment?

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Question 28

An investor purchasing a tranche that is rated AAA in a CLO is most likely to accept which of the following characteristics?

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Question 29

Which of the following is most likely to reduce an issuer's leverage after selling loans to an SPE?

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Question 30

Which of the following ABS features specifically helps investors when a securitized pool is first issued and the trust acquires additional qualifying assets post-closing?

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Question 31

Which of these statements about CMBS prepayment risk is correct?

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Question 32

An investor wants exposure only to principal prepayments from a mortgage pool. Which security should they choose?

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Question 33

Which aspect of securitization most directly helps banks expand origination beyond their balance sheets?

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Question 34

Which of the following statements about CLO collateral pools is true?

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Question 35

Which event would most likely trigger early amortization (rapid amortization) in a credit card ABS during the revolving period?

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Question 36

What is the primary credit risk investors face in a true-sale securitization (SPE issues ABS)?

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Question 37

Which of the following is a defining characteristic of a collateralized mortgage obligation (CMO)?

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Question 38

For a securitization with four tranches A (senior), B, C, D (junior), which of the following best describes how ratings are typically assigned to each tranche?

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Question 39

Which of the following best describes the legal protection investors obtain from an SPE structure?

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Question 40

If a CLO was created with USD700 million of debt promises and requires USD840 million of loan purchases, the overcollateralization ratio equals:

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Question 41

Which securitization investor benefit is best described as the ability to tailor interest rate exposure, credit exposure, and maturities to specific needs?

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Question 42

When a mortgage pass-through pool has both scheduled principal and unscheduled prepayments, which single statistic gives an estimate of when the MBS can be expected to be paid off on average?

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Question 43

Which of the following is NOT commonly a role of the servicer in an ABS transaction?

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Question 44

Which characteristic most distinguishes CMBS from RMBS in terms of loan pool composition?

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Question 45

Which of the following best captures why investors might prefer agency RMBS to non-agency RMBS?

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Question 46

Which term describes the difference between the coupon earned on collateral and the coupon paid on ABS securities that can be used to absorb shortfalls?

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Question 47

An RMBS pool's weighted average coupon (WAC) is 4.5% and servicing fees are 0.5%; what pass-through coupon does that imply ignoring other fees?

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Question 48

Which statement about CLO equity tranches is most accurate?

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Question 49

Which of the following securitization documents describes the transaction structure, priority of payments, and credit enhancements offered to investors?

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Question 50

Which of the following is the best summary of a covered bond's investor recourse?

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