FAILURE MAP
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FA-71276 / Weather index computation / Open access

Aviation flight category: IFR visibility edge · case 01

Exactly 3 statute miles is reported IFR.

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

ROOT CAUSE

The IFR visibility band includes 3 miles.

VERIFIED REPAIR

IFR visibility is 1 to below 3 miles.

Unsuccessful approach: Rounding visibility to whole miles reports 2.75 miles as MVFR.

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[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 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]]]
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 fixtureActualExpectedOutcome
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 3 layers [['BKN', 1000]][1000, 'IFR'][1000, 'MVFR']Failed
2.6 sm mist[None, 'IFR'][None, 'IFR']Passed

SHA-256 / a28dd8cadd11f4d882253f5341b01f420eecce85365fd55b36fd1899d8e4da8d

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 round(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 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]]]
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 fixtureActualExpectedOutcome
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 3 layers [['BKN', 1000]][1000, 'MVFR'][1000, 'MVFR']Passed
2.6 sm mist[None, 'MVFR'][None, 'IFR']Failed

SHA-256 / d558a4ac894b2254f19099503a9b68c605f17fc58f383fdfa1392981e47fc568

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 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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 3 layers [['BKN', 5000]]", [3, [['BKN', 5000]]], [5000, 'MVFR']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]], [["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']], ['2.75 sm haze', [2.75, [['FEW', 5000]]], [None, 'IFR']]], [["vis 3 layers [['BKN', 1000]]", [3, [['BKN', 1000]]], [1000, 'MVFR']], ["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']], ['2.6 sm mist', [2.6, []], [None, 'IFR']]]]
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 fixtureActualExpectedOutcome
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 3 layers [['BKN', 1000]][1000, 'MVFR'][1000, 'MVFR']Passed
2.6 sm mist[None, 'IFR'][None, 'IFR']Passed

SHA-256 / 9289cc6d68d2407c6a7972ad6b1e8153ca7f2e838eebf39dacdc7b77fa98d5ba

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 2026-09-29T14:48:28.185814+00:00.

Case digest / afb6ad1b363392130b521670803f3e479e7e9b3aa062236680cf630dbd878756