Emergency Exit Configuration

Emergency Exit Configuration (vehicle-design/sizing/emergency-exit-configuration)

Use when the task is checking a passenger emergency exit configuration against the discrete certification rules: each exit type carries a minimum rectangular opening and a per-exit seating credit, the exits on EACH side of the fuselage alone must cover the passenger capacity (an emergency can make one side unusable, so a side that relies on the other side is not adequate), the capacity band sets minimum exit counts and minimum types, a Type A, B or C exit forces a second Type C or larger exit on the same side, consecutive same-side exits must sit within the 60 ft adjacent-exit spacing rule, and the aggregate evacuation demand ratio closes the check. The per-side capacity sums, the adequacy verdict with the failing-rule list, the required per-side exit set, and the demand ratio gate the exit configuration. It pairs with fuselage-sizing, which sizes the cabin from the seat layout and names exits only as certification context, and with aircraft-oxygen-system-sizing, the other emergency provision; evacuation dynamics, aisle and assist-space access layout, exit door mechanisms, and ditching, ventral, tailcone and flightcrew exit provisions are out of scope (access rules and those provisions are not encoded, disclosed below).

Domain quick reference

• Exit type table (module constant, paraphrase of the public regulatory type definitions and the per-exit credit table; far-25 referenced, not reproduced): type id, minimum rectangular opening width x height in inches, per-exit seating credit: A 42 x 72, credit 110; B 32 x 72, credit 75; C 30 x 48, credit 55; I 24 x 48, credit 45; II 20 x 44, credit 40; III 20 x 36, credit 35; IV 19 x 26, credit 9. The credit encodes the maximum seating that follows from the type and number of exits installed on that side.
• Per-side rule: the exit credit sum on each side of the fuselage alone must cover the passenger capacity, because an emergency can make one side unusable.
• Capacity bands (paraphrase of the discrete type-and-number rules): 1-9 seats, one exit per side of Type IV or larger; 10-19 seats, one Type III or larger per side; 20-40 seats, two exits per side with one Type II or larger; 41-110 seats, two exits per side with one Type I or larger; more than 110 seats, at least two Type I or larger exits per side with every exit Type III or larger.
• Two-C-or-larger rule: when any Type A, B or C exit is installed on a side, that side must carry at least two exits of Type C or larger.
• Spacing rule: consecutive exits on the same side are separated by the row difference times the seat pitch converted to feet; a centerline gap above 60 ft is a spacing violation. The implied maximum seat distance to an exit is half the largest adjacent gap, the farthest any seat between two exits can sit from the nearer one.
• Aggregate evacuation demand ratio: passenger capacity over the sum of the exit credits, at or below 1.0 when the aggregate exit capacity covers the cabin.
• FAR-25 (14 CFR Part 25) sets the certification context for transport emergency exit types and counts and is referenced, not reproduced (standards-map.yaml, far-25).

Workflow

1. Collect the configuration: the passenger capacity, the exit types installed on the left and right sides of the fuselage, and the row numbers of the exits on the side checked for spacing.
2. Look up each installed type with exit_type_dimensions, confirming the minimum rectangular opening (width_in, height_in) and the per-exit seating credit from the module constant table.
3. Sum the per-side seating credits with side_exit_capacity: each side alone must cover the passenger capacity.
4. Read the capacity band and the required per-side exit set with capacity_band and required_exits_by_capacity: the band label, the minimum exit count per side, and the smallest-count per-side type multiset whose credit sum covers the capacity honoring the band minimum types (exact enumeration over combinations with replacement up to 12 exits per side, ties broken by the smaller excess).
5. Run the exit-count-check with exit_count_check(passenger_capacity, left_exits, right_exits): the verdict dict reports each side's capacity sum and failing-rule list, the adequate flag, and the shortfall (capacity minus the smaller of the two side sums). Failures are capacity, minimum-exit-count, all-exits-minimum-type, one-exit-minimum-type, two-exits-minimum-type, and two-C-or-larger-when-ABC-installed.
6. Check the 60 ft adjacent-exit spacing rule with exit_placement_check(exit_row_numbers, seat_pitch_in): adjacent gaps in feet, spacing violations above the 60 ft limit, the adequate flag, and the implied maximum seat distance to an exit (half the largest adjacent gap).
7. Compute the aggregate evacuation demand ratio with evacuation_demand_ratio(passenger_capacity, exit_capacity_sum): capacity over the exit credit sum, adequate aggregate at or below 1.0.

Worked example

180-seat single-aisle cabin (real module outputs):

• required_exits_by_capacity(180): band ">110", required per side ["A", "B"], covered 185, excess seats 5.
• exit_count_check(180, ["A", "C"], ["A", "C"]): left and right capacity 165, adequate False, failures ["capacity"] on both sides, shortfall 15.
• exit_count_check(180, ["A", "B"], ["A", "B"]): capacities 185 both sides, adequate True, no failures.
• evacuation_demand_ratio(180, 165) = 1.090909 (inadequate aggregate); evacuation_demand_ratio(180, 185) = 0.972973 (adequate aggregate).

60-seat regional:

• required_exits_by_capacity(60): band "41-110", required per side ["I", "III"], covered 80, excess 20 (one Type I floor-level exit plus one Type III overwing exit per side).
• exit_count_check(60, ["C", "I"], ["C", "I"]): adequate False, failures ["two-C-or-larger-when-ABC-installed"] both sides: the Type C door forces a second Type C or larger exit on that side.
• exit_count_check(60, ["C", "C"], ["C", "C"]): adequate True.
• exit_count_check(60, ["C"], ["C"]): left capacity 55, failures ["capacity", "minimum-exit-count", "two-C-or-larger-when-ABC-installed"].

Placement at 32 inch seat pitch: exits at rows 1, 12, 23 and 32 give adjacent gaps 29.3333, 29.3333 and 24.0 ft, adequate True, implied maximum seat distance 14.667 ft. Exits only at rows 1 and 32 leave an 82.6667 ft gap: adequate False, spacing_violations [(1, 82.6667)]. Regional 20 rows at 31 inch pitch with exits at rows 1 and 20 give a 49.0833 ft gap: adequate True, implied maximum seat distance 24.542 ft.

Pitfalls

• Treating the two sides as shared capacity: the per-side rule demands that each side alone covers the passenger capacity; a configuration whose sides only cover the cabin together fails the check.
• Checking the credit sum but skipping the type rules: a Type A pair on 60 seats may cover the capacity while a Type C plus Type I pair fails the two-C-or-larger rule that the Type C install triggers.
• Reading the band minimum count as optional: a single exit of any type per side always fails the 41-110 and 20-40 bands, however large the door.
• Forgetting the over-110 minimum types: on more than 110 seats every exit must be Type III or larger, so a Type IV anywhere on a side fails all-exits-minimum-type even when the credits look generous.
• Mixing the spacing rule across sides: the 60 ft limit applies to consecutive exits on the SAME side, never across the fuselage.
• Forgetting the unit conversion: adjacent gaps are the row difference times the pitch in inches divided by 12; 32 inches of pitch is 2.6667 ft per row.
• Confusing the per-side required exit set with the aggregate demand ratio: the first is a per-side minimum configuration, the second totals the installed credits over the cabin.
• Passing non-physical inputs (capacity 0, empty row lists, zero pitch, unknown exit types); the module raises ValueError instead of returning a nonsense verdict.

Verification

Deterministic, offline checks (scripts/test_emergency_exit_configuration.py): the worked-example anchors above with the module's real outputs as assert targets; the full seven-type exit type table; the two Type A credit identity (220) and the single Type IV credit identity (9); the capacity-band boundary mapping; the covered minus capacity equals excess identity; the exit-count-check verdicts of the worked example with the failing-rule lists asserted exactly; the one-exit-minimum-type and two-exits-minimum-type band checks; the independence of the two sides; the adjacent-gap anchors 29.3333, 24.0, 82.6667 and 49.0833 ft with the implied maximum seat distance; evacuation demand ratio anchors 1.090909 and 0.972973 within 1e-5 and the unity ratio at equal credit sums; ValueError rejection of unknown exit types, capacity below 1, exit capacity sum 0, empty or non-positive row lists and zero pitch; and repeated-call determinism with the documented dict keys.

Related leaves

• vehicle-design/sizing/fuselage-sizing
• vehicle-design/sizing/aircraft-oxygen-system-sizing
• vehicle-design/sizing/fire-protection-sizing

Behavior contract (gate 3)

The discrete emergency exit configuration logic is exercised by the gate 3 contract test: scripts/test_emergency_exit_configuration.py against scripts/emergency_exit_configuration_logic.py (stdlib unittest, offline). Run:

python3 scripts/test_emergency_exit_configuration.py

Compliance

• Standards referenced, not reproduced: the exit type definitions and the per-exit credit table are paraphrased into the module constant table per standards-map.yaml; far-25 regulation text is never reproduced verbatim.
• compliance: STANDARDS-REF, gated: false.