# L31 Pre-flight **Block 4: Aircraft Survivability and Mission Planning — Lesson 31: Survivability and the PK Chain** *Work this before L31. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.* --- ## Assumed pre-class reading - L1's kill chain (Detect → Track → Identify → Engage → Kill) and the idea that breaking any one link saves the aircraft. - The Jupyter Book Reading page for L31 — Ball's split of survivability into susceptibility $P_H$ and vulnerability $P_{K|H}$, the chain as a product of conditional probabilities, Ball's two toolkits, $P_S = \prod_i (1 - P_{K,i})$ across independent encounters, and additive risk $r = -\ln P_S$. --- ## Quiz questions (5 items, ~5 minutes) **Q1.** (Mark all that apply) A B-21 flies the same route against the same air defense. Mark every change below that reduces its **susceptibility** ($P_H$, the chance it is hit) rather than its vulnerability. - [ ] (a) A radar-warning receiver that tells the crew a SAM has locked on, in time to turn away - [ ] (b) Two hydraulic systems routed down opposite sides of the fuselage - [ ] (c) A flare dispenser that seduces an IR seeker in its terminal phase - [ ] (d) Foam in the fuel tanks that keeps a fragment hit from igniting the fuel vapor - [ ] (e) An escort that destroys the SAM's engagement radar before the ingress --- **Q2.** (Mark all that apply) Same aircraft, same route. Mark every change below that reduces its **vulnerability** ($P_{K|H}$, the chance that a hit kills it). - [ ] (a) Moving the flight-control computers away from the fuel tanks and the engine bays - [ ] (b) Radar-absorbing material applied to the engine inlet lips - [ ] (c) An engine-bay fire detector wired to an automatic extinguisher - [ ] (d) An armor plate between the most likely hit direction and the crew station - [ ] (e) A self-protection jammer that walks the tracking radar's range gate off the aircraft --- **Q3.** (Multiple choice) A route meets three SAM sites, and each fires one independent shot with $P_K = 0.10$, $0.25$ and $0.05$. The mission's survival probability $P_S$ is: - [ ] (a) 0.600 - [ ] (b) 0.641 - [ ] (c) 0.750 - [ ] (d) 0.867 --- **Q4.** (Multiple choice) L34 will plan routes with a shortest-path search that minimizes a **sum** of per-encounter costs. Why should each encounter's cost be $r_i = -\ln(1 - P_{K,i})$ rather than $P_{K,i}$ itself? - [ ] (a) Its sum is exactly $-\ln P_S$, so the route with the least total cost is the most survivable - [ ] (b) It is always smaller than $P_{K,i}$, so the planner cannot overstate a route's risk - [ ] (c) A sum of $P_{K,i}$ values can pass 1, and the log keeps the total cost below one - [ ] (d) It weights low-$P_K$ encounters more heavily, so the planner avoids many small threats --- **Q5.** (Short answer) For each lever, say whether it is susceptibility or vulnerability reduction, name Ball's concept, and name the factor of $P_K = P_D\,P_{T|D}\,P_{I|T}\,P_{H|I}\,P_{K|H}$ it shrinks: (i) a low-altitude ingress that keeps the aircraft below a SAM radar's horizon until the last minutes of the run; (ii) replacing a hydraulic flight-control actuator with an electric one that has no fluid to leak or burn.