FA-71266 / Weather index computation / Open access

Aviation flight category: worse-of combination · case 01

Fog with a high ceiling is reported VFR.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The better of the ceiling and visibility categories is reported.

VERIFIED REPAIR

Report the more restrictive category.

Unsuccessful approach: Using the ceiling alone ignores low visibility.

Case contract

layers are [cover, height_ft]; the ceiling is the lowest BKN, OVC or VV layer (None if none). Ceiling class: None or >3000 VFR, 1000-3000 MVFR, 500-999 IFR, <500 LIFR. Visibility class: >5 VFR, 3-5 MVFR, 1 to <3 IFR, <1 LIFR. Report [ceiling, worse of the two classes].

Why this case matters

Pilots and dispatch use flight categories for go/no-go and alternate planning.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(vis_sm, layers):
    ceil = None
    for cover, h in layers:
        if cover in ("BKN", "OVC", "VV"):
            if ceil is None or h < ceil:
                ceil = h
    def cls_c(c):
        if c is None:
            return 3
        if c < 500:
            return 0
        if c < 1000:
            return 1
        if c <= 3000:
            return 2
        return 3
    def cls_v(v):
        if v < 1:
            return 0
        if v < 3:
            return 1
        if v <= 5:
            return 2
        return 3
    names = ["LIFR", "IFR", "MVFR", "VFR"]
    return [ceil, names[max(cls_c(ceil), cls_v(vis_sm))]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[["vis 4 layers [['BKN', 400]]", [4, [['BKN', 400]]], [400, 'LIFR']], ["vis 5 layers [['FEW', 2500]]", [5, [['FEW', 2500]]], [None, 'MVFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]", [0.5, [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]], [1500, 'LIFR']], ["vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]", [2, [['OVC', 400], ['SCT', 5000], ['SCT', 200]]], [400, 'LIFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']]], [["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["vis 3 layers [['SCT', 5000], ['FEW', 200]]", [3, [['SCT', 5000], ['FEW', 200]]], [None, 'MVFR']], ["vis 2 layers [['SCT', 5000]]", [2, [['SCT', 5000]]], [None, 'IFR']], ['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 500], ['BKN', 5000]]", [6, [['BKN', 500], ['BKN', 5000]]], [500, 'IFR']], ["vis 5 layers [['BKN', 3100]]", [5, [['BKN', 3100]]], [3100, 'MVFR']], ["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']]], [['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 4 layers [['VV', 2500]]", [4, [['VV', 2500]]], [2500, 'MVFR']], ["vis 0.25 layers [['FEW', 5000]]", [0.25, [['FEW', 5000]]], [None, 'LIFR']], ["vis 1 layers [['OVC', 500]]", [1, [['OVC', 500]]], [500, 'IFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 10 layers [['FEW', 1500], ['OVC', 3000]]", [10, [['FEW', 1500], ['OVC', 3000]]], [3000, 'MVFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']]], [['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 0.5 layers [['FEW', 400], ['VV', 400]]", [0.5, [['FEW', 400], ['VV', 400]]], [400, 'LIFR']], ["vis 0.25 layers [['BKN', 400], ['BKN', 200]]", [0.25, [['BKN', 400], ['BKN', 200]]], [200, 'LIFR']], ["vis 10 layers [['SCT', 3100]]", [10, [['SCT', 3100]]], [None, 'VFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 10 layers []', [10, []], [None, 'VFR']], ["vis 5 layers [['BKN', 500]]", [5, [['BKN', 500]]], [500, 'IFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']]], [["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']], ["vis 3 layers [['SCT', 400]]", [3, [['SCT', 400]]], [None, 'MVFR']], ["vis 1 layers [['VV', 2500]]", [1, [['VV', 2500]]], [2500, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']], ["vis 3 layers [['FEW', 500], ['SCT', 1000], ['OVC', 400]]", [3, [['FEW', 500], ['SCT', 1000], ['OVC', 400]]], [400, 'LIFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ["vis 3 layers [['FEW', 200]]", [3, [['FEW', 200]]], [None, 'MVFR']], ["vis 5 layers [['SCT', 5000]]", [5, [['SCT', 5000]]], [None, 'MVFR']]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
vis 4 layers [['BKN', 400]]	`[400, 'MVFR']`	`[400, 'LIFR']`	Failed
vis 5 layers [['FEW', 2500]]	`[None, 'VFR']`	`[None, 'MVFR']`	Failed
vis 0.5 layers []	`[None, 'VFR']`	`[None, 'LIFR']`	Failed
vis 6 layers [['BKN', 3000]]	`[3000, 'VFR']`	`[3000, 'MVFR']`	Failed
vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]	`[1500, 'MVFR']`	`[1500, 'LIFR']`	Failed
vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]	`[400, 'IFR']`	`[400, 'LIFR']`	Failed
vis 0.5 layers []	`[None, 'VFR']`	`[None, 'LIFR']`	Failed
vis 3 layers [['BKN', 1000]]	`[1000, 'MVFR']`	`[1000, 'MVFR']`	Passed

SHA-256 / 4ee0a5a0d70ecffc997684b244efaf859710c62dcd583122967d860494fbebff

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(vis_sm, layers):
    ceil = None
    for cover, h in layers:
        if cover in ("BKN", "OVC", "VV"):
            if ceil is None or h < ceil:
                ceil = h
    def cls_c(c):
        if c is None:
            return 3
        if c < 500:
            return 0
        if c < 1000:
            return 1
        if c <= 3000:
            return 2
        return 3
    def cls_v(v):
        if v < 1:
            return 0
        if v < 3:
            return 1
        if v <= 5:
            return 2
        return 3
    names = ["LIFR", "IFR", "MVFR", "VFR"]
    return [ceil, names[cls_c(ceil)]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[["vis 4 layers [['BKN', 400]]", [4, [['BKN', 400]]], [400, 'LIFR']], ["vis 5 layers [['FEW', 2500]]", [5, [['FEW', 2500]]], [None, 'MVFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]", [0.5, [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]], [1500, 'LIFR']], ["vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]", [2, [['OVC', 400], ['SCT', 5000], ['SCT', 200]]], [400, 'LIFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']]], [["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["vis 3 layers [['SCT', 5000], ['FEW', 200]]", [3, [['SCT', 5000], ['FEW', 200]]], [None, 'MVFR']], ["vis 2 layers [['SCT', 5000]]", [2, [['SCT', 5000]]], [None, 'IFR']], ['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 500], ['BKN', 5000]]", [6, [['BKN', 500], ['BKN', 5000]]], [500, 'IFR']], ["vis 5 layers [['BKN', 3100]]", [5, [['BKN', 3100]]], [3100, 'MVFR']], ["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']]], [['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 4 layers [['VV', 2500]]", [4, [['VV', 2500]]], [2500, 'MVFR']], ["vis 0.25 layers [['FEW', 5000]]", [0.25, [['FEW', 5000]]], [None, 'LIFR']], ["vis 1 layers [['OVC', 500]]", [1, [['OVC', 500]]], [500, 'IFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 10 layers [['FEW', 1500], ['OVC', 3000]]", [10, [['FEW', 1500], ['OVC', 3000]]], [3000, 'MVFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']]], [['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 0.5 layers [['FEW', 400], ['VV', 400]]", [0.5, [['FEW', 400], ['VV', 400]]], [400, 'LIFR']], ["vis 0.25 layers [['BKN', 400], ['BKN', 200]]", [0.25, [['BKN', 400], ['BKN', 200]]], [200, 'LIFR']], ["vis 10 layers [['SCT', 3100]]", [10, [['SCT', 3100]]], [None, 'VFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 10 layers []', [10, []], [None, 'VFR']], ["vis 5 layers [['BKN', 500]]", [5, [['BKN', 500]]], [500, 'IFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']]], [["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']], ["vis 3 layers [['SCT', 400]]", [3, [['SCT', 400]]], [None, 'MVFR']], ["vis 1 layers [['VV', 2500]]", [1, [['VV', 2500]]], [2500, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']], ["vis 3 layers [['FEW', 500], ['SCT', 1000], ['OVC', 400]]", [3, [['FEW', 500], ['SCT', 1000], ['OVC', 400]]], [400, 'LIFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ["vis 3 layers [['FEW', 200]]", [3, [['FEW', 200]]], [None, 'MVFR']], ["vis 5 layers [['SCT', 5000]]", [5, [['SCT', 5000]]], [None, 'MVFR']]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
vis 4 layers [['BKN', 400]]	`[400, 'LIFR']`	`[400, 'LIFR']`	Passed
vis 5 layers [['FEW', 2500]]	`[None, 'VFR']`	`[None, 'MVFR']`	Failed
vis 0.5 layers []	`[None, 'VFR']`	`[None, 'LIFR']`	Failed
vis 6 layers [['BKN', 3000]]	`[3000, 'MVFR']`	`[3000, 'MVFR']`	Passed
vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]	`[1500, 'MVFR']`	`[1500, 'LIFR']`	Failed
vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]	`[400, 'LIFR']`	`[400, 'LIFR']`	Passed
vis 0.5 layers []	`[None, 'VFR']`	`[None, 'LIFR']`	Failed
vis 3 layers [['BKN', 1000]]	`[1000, 'MVFR']`	`[1000, 'MVFR']`	Passed

SHA-256 / 54fcd44420ba73848fa09ab3a4fa723a722e361d8b2bb601eca5ca96a736e383

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(vis_sm, layers):
    ceil = None
    for cover, h in layers:
        if cover in ("BKN", "OVC", "VV"):
            if ceil is None or h < ceil:
                ceil = h
    def cls_c(c):
        if c is None:
            return 3
        if c < 500:
            return 0
        if c < 1000:
            return 1
        if c <= 3000:
            return 2
        return 3
    def cls_v(v):
        if v < 1:
            return 0
        if v < 3:
            return 1
        if v <= 5:
            return 2
        return 3
    names = ["LIFR", "IFR", "MVFR", "VFR"]
    return [ceil, names[min(cls_c(ceil), cls_v(vis_sm))]]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[["vis 4 layers [['BKN', 400]]", [4, [['BKN', 400]]], [400, 'LIFR']], ["vis 5 layers [['FEW', 2500]]", [5, [['FEW', 2500]]], [None, 'MVFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]", [0.5, [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]], [1500, 'LIFR']], ["vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]", [2, [['OVC', 400], ['SCT', 5000], ['SCT', 200]]], [400, 'LIFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']]], [["vis 6 layers [['BKN', 3000]]", [6, [['BKN', 3000]]], [3000, 'MVFR']], ["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["vis 3 layers [['SCT', 5000], ['FEW', 200]]", [3, [['SCT', 5000], ['FEW', 200]]], [None, 'MVFR']], ["vis 2 layers [['SCT', 5000]]", [2, [['SCT', 5000]]], [None, 'IFR']], ['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 6 layers [['BKN', 500], ['BKN', 5000]]", [6, [['BKN', 500], ['BKN', 5000]]], [500, 'IFR']], ["vis 5 layers [['BKN', 3100]]", [5, [['BKN', 3100]]], [3100, 'MVFR']], ["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']]], [['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 4 layers [['VV', 2500]]", [4, [['VV', 2500]]], [2500, 'MVFR']], ["vis 0.25 layers [['FEW', 5000]]", [0.25, [['FEW', 5000]]], [None, 'LIFR']], ["vis 1 layers [['OVC', 500]]", [1, [['OVC', 500]]], [500, 'IFR']], ['vis 0.5 layers []', [0.5, []], [None, 'LIFR']], ["vis 10 layers [['FEW', 1500], ['OVC', 3000]]", [10, [['FEW', 1500], ['OVC', 3000]]], [3000, 'MVFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']]], [['vis 0.25 layers []', [0.25, []], [None, 'LIFR']], ["vis 0.5 layers [['FEW', 400], ['VV', 400]]", [0.5, [['FEW', 400], ['VV', 400]]], [400, 'LIFR']], ["vis 0.25 layers [['BKN', 400], ['BKN', 200]]", [0.25, [['BKN', 400], ['BKN', 200]]], [200, 'LIFR']], ["vis 10 layers [['SCT', 3100]]", [10, [['SCT', 3100]]], [None, 'VFR']], ['vis 1 layers []', [1, []], [None, 'IFR']], ['vis 10 layers []', [10, []], [None, 'VFR']], ["vis 5 layers [['BKN', 500]]", [5, [['BKN', 500]]], [500, 'IFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']]], [["vis 0.5 layers [['SCT', 2500]]", [0.5, [['SCT', 2500]]], [None, 'LIFR']], ["vis 3 layers [['SCT', 400]]", [3, [['SCT', 400]]], [None, 'MVFR']], ["vis 1 layers [['VV', 2500]]", [1, [['VV', 2500]]], [2500, 'IFR']], ['vis 6 layers []', [6, []], [None, 'VFR']], ["vis 3 layers [['FEW', 500], ['SCT', 1000], ['OVC', 400]]", [3, [['FEW', 500], ['SCT', 1000], ['OVC', 400]]], [400, 'LIFR']], ["vis 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ["vis 3 layers [['FEW', 200]]", [3, [['FEW', 200]]], [None, 'MVFR']], ["vis 5 layers [['SCT', 5000]]", [5, [['SCT', 5000]]], [None, 'MVFR']]]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
vis 4 layers [['BKN', 400]]	`[400, 'LIFR']`	`[400, 'LIFR']`	Passed
vis 5 layers [['FEW', 2500]]	`[None, 'MVFR']`	`[None, 'MVFR']`	Passed
vis 0.5 layers []	`[None, 'LIFR']`	`[None, 'LIFR']`	Passed
vis 6 layers [['BKN', 3000]]	`[3000, 'MVFR']`	`[3000, 'MVFR']`	Passed
vis 0.5 layers [['SCT', 800], ['BKN', 1500], ['BKN', 2500]]	`[1500, 'LIFR']`	`[1500, 'LIFR']`	Passed
vis 2 layers [['OVC', 400], ['SCT', 5000], ['SCT', 200]]	`[400, 'LIFR']`	`[400, 'LIFR']`	Passed
vis 0.5 layers []	`[None, 'LIFR']`	`[None, 'LIFR']`	Passed
vis 3 layers [['BKN', 1000]]	`[1000, 'MVFR']`	`[1000, 'MVFR']`	Passed

SHA-256 / a1a0a69995c7fbcbdf2b806ad679ef5c63af34b57a5ec97c2e905b1447ee931e

Verification & scope

Stipulated deterministic teaching model of an operational weather index; coefficients and thresholds are fixed by the contract and no claim of standards conformance is made. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:48:28.060777+00:00.

Case digest / 7f28b350e1db05d252539ab788ccfb48c1915ebac642abb80932bd854e4f7868