1. Legal Architecture for Stress Scenarios

a) PFMI (2012) - Global standard

• Principle 4: Credit risk - Cover-2 standard. CCP must hold prefunded resources to cover default of the 2 largest clearing members and their affiliates under extreme but plausible scenarios.
• Principle 6: Margin - Initial margin 99% confidence for exchange-traded, 99.5% for OTC.
• Principle 7: Liquidity risk - Daily stress tests using standard and predetermined parameters, monthly comprehensive review.
• Principle requires clear procedures to report stress test results to decision makers.

b) EMIR
Goes further than PFMI. Requires:

• No disclosure requirement for stress test details under PFMI, but EMIR requires disclosure to regulators and annual EU-wide stress test by ESMA.
• Confidence 99% for listed, 99.5% for OTC derivatives for initial margin.
• Daily stress testing, monthly sensitivity analysis, annual validation.

c) US - CFTC & SEC
CFTC runs systemic supervisory stress tests. In its 2nd test, CFTC tested CME, ICE Clear US and LCH Ltd for settlement liquidity failure of same two systemically important clearing members at each clearinghouse. All passed.

2. Types of Stress Scenarios CCPs Must Run

1. Credit Stress Scenarios - Sizing the Default Fund

• Historical scenarios: Replay 1987 crash, 2008 Lehman, 2020 COVID, 2022 UK Gilt crisis, 2022 Nickel squeeze.
• Hypothetical scenarios: Parallel yield curve +300bps, equity -30%, commodities +50%, FX volatility spike.
• Cover-2, Cover-4, Cover-X: ESMA's 5th exercise uses:
  • Cover-2: default of 2 largest members
  • Cover-X: default of all members in a category - non-financial, non-bank.
  • ESMA also tested Cover-4 with doubled liquidation horizon - noted as significantly more severe than extreme but plausible.

2. Liquidity Stress Scenarios
Not enough to have resources, need cash when needed. Tests failure of settlement banks, custodians, investment counterparties.

• EMIR Art 44: Need liquid resources to cover default of at least 2 largest members.
• Custody risk: Custodians that keep resources of CCP subject to severe stress preventing meeting obligations.

3. Concentration & Wrong-Way Risk
ESMA includes concentration risk - what if defaulting member is 40% of open interest in a product? PFMI requires add-ons.

4. Reverse Stress Testing
ESMA 5th exercise: gradually increase number of defaulting entities, severity of shock, and level of concentration risk to model at which point CCPs' resources become exhausted.
Purpose is to find breaking point beyond Cover-2.

5. Investment & Collateral Stress
Government or repo counterparty default could lead to investment losses.

3. The Default Waterfall and Where Stress Bites

Under PFMI/EMIR each CCP has a "waterfall scenario" for management of member defaults in extreme but plausible conditions.

1. Defaulter's Initial Margin + Default Fund contribution
2. CCP Skin-in-the-game (SITG) - typically 15-25% of capital. Average SITG is only ∼3% of waterfall across major CCPs.
3. Mutualized Default Fund of non-defaulters
4. Further SITG
5. Powers of assessment / Recovery: Variation Margin Gains Haircutting (VMGH), Cash calls

4. Case Laws / Real Defaults - The Stress Tests That Failed

Case 1: Nasdaq Clearing AB - Einar Aas Default - 10-11 September 2018 - The Landmark Case

Facts: Einar Aas, Norwegian power trader, natural person admitted as individual clearing member in commodities. Held large spread position Nordic vs German power. Price spread moved sharply.
Nasdaq made margin call that Aas failed to pay in full, declared in default next morning.

CCP auctioned portfolio to 4 members. Winning bid created loss of €114 million in excess of collateral Aas provided.

Waterfall: Initial margin exhausted, then CCP's SITG (€7m) wiped, then €107m of commodities default fund mutualized - two-thirds of fund consumed, surviving members required to replenish $107 million within few days.

Legal / Regulatory Findings:

• Norwegian Finanstilsynet called it breach of EMIR margin rules - risk models underappreciated volatility and prescribed insufficient margins.
• BIS paper: near-failure of NASDAQ Clearing profoundly shocked observers, as it happened amid calm market conditions. Main problem was CCP's risk models underappreciated potential level of volatility.
• FIA stated: first use of a default fund by a major CCP since KRX default in 2013.

Lesson: Stress scenarios must include concentrated, directional, illiquid positions of non-bank individuals, not just bank members.

Case 2: Lehman Brothers - LCH SwapClear - September 2008

Lehman had derivative portfolios at a number of CCPs. LCH had to unwind 66,390 interest rate swap trades, $9 trillion notional. Used about a third of margin held, so neither CCP nor members sustained losses. Cited as successful default management vs. Nasdaq failure.

Legal issue: Portability and close-out netting under English law upheld. No litigation against CCP, validated default management process.

Case 3: KRX - HanMag Securities - December 2013

Small member HanMag defaulted on KOSPI 200 options due to fat-finger error. Loss KRW 46bn exceeded margin, ate through KRX default fund. First Asian CCP default fund use. Led to PFMI reform on Cover-2 and concentration add-ons.

Case 4: MF Global - 2011 - Liquidity Stress Precursor

Leveraged positions resulted in firm's inability to meet margin calls. CCPs (LCH, CME) declared default and ported client positions. No CCP loss but triggered debate on client asset protection and liquidity stress - CFTC later introduced liquidity Cover-2.

Case 5: LCH.Clearnet Rulebook & VMGH - Legal Enforceability

LCH rulebook provides that in event of VMGH, any recoveries LCH makes from defaulting clearing member should be used to reimburse non-defaulting members pro rata.
UK High Court cases (e.g., LCH Ltd v. Client positions) have upheld that VMGH and assessment powers are contractual and enforceable if in rulebook and disclosed, even if they cause losses to pension funds - establishing that stress scenario recovery tools are not ultra vires.

5. What Regulators Now Require After These Cases

ESMA 5th stress test 2024-2026 framework:

• Baseline + Adverse scenario provided by ESRB
• Credit, liquidity, concentration, reverse stress in one exercise
• Disclosure of methodology but not individual CCP stress parameters - ongoing debate raised by BoE Governor Bailey that EMIR should require disclosure of stress details which ultimately determines size of default funds.

Takeaway for counsel:
A CCP is legally compliant only if its stress scenarios are:

1. Extreme but plausible + reverse stress to exhaustion
2. Cover at least 2 largest members under 99.9% confidence (ESMA uses 99.9% for default fund vs 99.5% for margin)
3. Include liquidity, concentration, and custody failure
4. Validated by independent risk and college of supervisors

Failure to do so = breach of EMIR Art 49 and PFMI 4, leading to Finanstilsynet-style fines as in Nasdaq Clearing - fined in 2021 after Einar Aas.