FA-65981 / Aviation weight and balance / Open access

Already-at-target request reported as a direction error · case 01

Asking to reach the CG the aircraft already has returns ERR_DIRECTION for aft station moves.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Without the zero-change guard, a zero dCG compares as non-positive against a positive arm change.

VERIFIED REPAIR

Return 0 whenever the target CG equals the current CG, before the direction test.

Unsuccessful approach: Guarding only forward station moves still reports an error when the no-op request names an aft station move.

Case contract

Input [total lb, current CG, target CG, from-station arm, to-station arm]. Weight to move = W*dCG/dArm, rounded UP to a whole pound after clearing float noise at 6 decimals. Same station -> 'ERR_SAME_STATION'; zero dCG -> 0; a move that shifts CG the wrong way -> 'ERR_DIRECTION'.

Why this case matters

The weight-shift formula moves existing load between stations without changing total weight; the answer must be conservative (rounded up).

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    W, cg0, cg1, a_from, a_to = x
    if a_from == a_to: return 'ERR_SAME_STATION'
    dcg = cg1 - cg0
    darm = a_to - a_from
    if (dcg > 0) != (darm > 0): return 'ERR_DIRECTION'
    moved = W * dcg / darm
    return math.ceil(round(moved, 6))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['baggage moved aft', [2400, 40.0, 41.1, 70.0, 120.0], 53], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2610, 46.5, 45.0, 140.0, 60.0], 49], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 69.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3980, 45.3, 44.23, 41.8, 92.7], 'ERR_DIRECTION'], ['sampled case 2', [2707, 38.32, 40.1, 125.8, 85.0], 'ERR_DIRECTION'], ['sampled case 3', [3239, 40.39, 40.5, 103.2, 113.0], 37]], [['baggage moved aft', [2400, 40.0, 41.2, 70.0, 120.0], 58], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2620, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 68.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2415, 40.34, 38.4, 91.5, 122.3], 'ERR_DIRECTION'], ['sampled case 2', [3730, 42.18, 40.8, 132.4, 79.3], 97], ['sampled case 3', [2931, 40.9, 40.9, 127.0, 108.6], 0]], [['baggage moved aft', [2400, 40.0, 41.3, 70.0, 120.0], 63], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2630, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 67.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3390, 43.8, 43.8, 81.2, 142.7], 0], ['sampled case 2', [2280, 42.43, 43.6, 91.3, 32.9], 'ERR_DIRECTION'], ['sampled case 3', [3550, 38.5, 38.5, 60.9, 57.1], 0]], [['baggage moved aft', [2400, 40.0, 41.4, 70.0, 120.0], 68], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2640, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 66.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2103, 45.94, 44.79, 82.0, 59.6], 108], ['sampled case 2', [1930, 43.1, 41.2, 104.4, 84.0], 180], ['sampled case 3', [2160, 40.97, 40.7, 113.1, 93.1], 30]], [['baggage moved aft', [2400, 40.0, 41.5, 70.0, 120.0], 72], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2650, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 65.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2243, 42.7, 42.6, 141.2, 133.0], 28], ['sampled case 2', [3954, 45.3, 43.62, 97.4, 126.8], 'ERR_DIRECTION'], ['sampled case 3', [3960, 41.6, 42.67, 35.8, 103.5], 63]]]
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
baggage moved aft	`53`	`53`	Passed
exact whole-pound shift	`10`	`10`	Passed
shift forward	`49`	`49`	Passed
wrong direction request	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
already at target	`ERR_DIRECTION`	`0`	Failed
same station	`ERR_SAME_STATION`	`ERR_SAME_STATION`	Passed
sampled case 1	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 2	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 3	`37`	`37`	Passed

SHA-256 / c5cddb327cb7872bb4ed31454aa1b765187ba2d2929c832919ef69cb2cf39086

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    W, cg0, cg1, a_from, a_to = x
    if a_from == a_to: return 'ERR_SAME_STATION'
    dcg = cg1 - cg0
    darm = a_to - a_from
    if dcg == 0 and darm < 0: return 0
    if (dcg > 0) != (darm > 0): return 'ERR_DIRECTION'
    moved = W * dcg / darm
    return math.ceil(round(moved, 6))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['baggage moved aft', [2400, 40.0, 41.1, 70.0, 120.0], 53], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2610, 46.5, 45.0, 140.0, 60.0], 49], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 69.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3980, 45.3, 44.23, 41.8, 92.7], 'ERR_DIRECTION'], ['sampled case 2', [2707, 38.32, 40.1, 125.8, 85.0], 'ERR_DIRECTION'], ['sampled case 3', [3239, 40.39, 40.5, 103.2, 113.0], 37]], [['baggage moved aft', [2400, 40.0, 41.2, 70.0, 120.0], 58], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2620, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 68.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2415, 40.34, 38.4, 91.5, 122.3], 'ERR_DIRECTION'], ['sampled case 2', [3730, 42.18, 40.8, 132.4, 79.3], 97], ['sampled case 3', [2931, 40.9, 40.9, 127.0, 108.6], 0]], [['baggage moved aft', [2400, 40.0, 41.3, 70.0, 120.0], 63], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2630, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 67.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3390, 43.8, 43.8, 81.2, 142.7], 0], ['sampled case 2', [2280, 42.43, 43.6, 91.3, 32.9], 'ERR_DIRECTION'], ['sampled case 3', [3550, 38.5, 38.5, 60.9, 57.1], 0]], [['baggage moved aft', [2400, 40.0, 41.4, 70.0, 120.0], 68], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2640, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 66.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2103, 45.94, 44.79, 82.0, 59.6], 108], ['sampled case 2', [1930, 43.1, 41.2, 104.4, 84.0], 180], ['sampled case 3', [2160, 40.97, 40.7, 113.1, 93.1], 30]], [['baggage moved aft', [2400, 40.0, 41.5, 70.0, 120.0], 72], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2650, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 65.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2243, 42.7, 42.6, 141.2, 133.0], 28], ['sampled case 2', [3954, 45.3, 43.62, 97.4, 126.8], 'ERR_DIRECTION'], ['sampled case 3', [3960, 41.6, 42.67, 35.8, 103.5], 63]]]
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
baggage moved aft	`53`	`53`	Passed
exact whole-pound shift	`10`	`10`	Passed
shift forward	`49`	`49`	Passed
wrong direction request	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
already at target	`ERR_DIRECTION`	`0`	Failed
same station	`ERR_SAME_STATION`	`ERR_SAME_STATION`	Passed
sampled case 1	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 2	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 3	`37`	`37`	Passed

SHA-256 / f7cf671aa62034d4c94279cfd65c8ef50cf86b75f0eba145a110515db42f7994

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
    W, cg0, cg1, a_from, a_to = x
    if a_from == a_to: return 'ERR_SAME_STATION'
    dcg = cg1 - cg0
    darm = a_to - a_from
    if dcg == 0: return 0
    if (dcg > 0) != (darm > 0): return 'ERR_DIRECTION'
    moved = W * dcg / darm
    return math.ceil(round(moved, 6))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['baggage moved aft', [2400, 40.0, 41.1, 70.0, 120.0], 53], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2610, 46.5, 45.0, 140.0, 60.0], 49], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 69.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3980, 45.3, 44.23, 41.8, 92.7], 'ERR_DIRECTION'], ['sampled case 2', [2707, 38.32, 40.1, 125.8, 85.0], 'ERR_DIRECTION'], ['sampled case 3', [3239, 40.39, 40.5, 103.2, 113.0], 37]], [['baggage moved aft', [2400, 40.0, 41.2, 70.0, 120.0], 58], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2620, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 68.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2415, 40.34, 38.4, 91.5, 122.3], 'ERR_DIRECTION'], ['sampled case 2', [3730, 42.18, 40.8, 132.4, 79.3], 97], ['sampled case 3', [2931, 40.9, 40.9, 127.0, 108.6], 0]], [['baggage moved aft', [2400, 40.0, 41.3, 70.0, 120.0], 63], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2630, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 67.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [3390, 43.8, 43.8, 81.2, 142.7], 0], ['sampled case 2', [2280, 42.43, 43.6, 91.3, 32.9], 'ERR_DIRECTION'], ['sampled case 3', [3550, 38.5, 38.5, 60.9, 57.1], 0]], [['baggage moved aft', [2400, 40.0, 41.4, 70.0, 120.0], 68], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2640, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 66.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2103, 45.94, 44.79, 82.0, 59.6], 108], ['sampled case 2', [1930, 43.1, 41.2, 104.4, 84.0], 180], ['sampled case 3', [2160, 40.97, 40.7, 113.1, 93.1], 30]], [['baggage moved aft', [2400, 40.0, 41.5, 70.0, 120.0], 72], ['exact whole-pound shift', [3000, 42.0, 42.3, 50.0, 140.0], 10], ['shift forward', [2650, 46.5, 45.0, 140.0, 60.0], 50], ['wrong direction request', [2500, 40.0, 41.0, 120.0, 65.0], 'ERR_DIRECTION'], ['already at target', [2300, 43.2, 43.2, 70.0, 120.0], 0], ['same station', [2300, 43.2, 44.0, 95.0, 95.0], 'ERR_SAME_STATION'], ['sampled case 1', [2243, 42.7, 42.6, 141.2, 133.0], 28], ['sampled case 2', [3954, 45.3, 43.62, 97.4, 126.8], 'ERR_DIRECTION'], ['sampled case 3', [3960, 41.6, 42.67, 35.8, 103.5], 63]]]
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
baggage moved aft	`53`	`53`	Passed
exact whole-pound shift	`10`	`10`	Passed
shift forward	`49`	`49`	Passed
wrong direction request	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
already at target	`0`	`0`	Passed
same station	`ERR_SAME_STATION`	`ERR_SAME_STATION`	Passed
sampled case 1	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 2	`ERR_DIRECTION`	`ERR_DIRECTION`	Passed
sampled case 3	`37`	`37`	Passed

SHA-256 / cd167eef2aaa94931353bfb051f692c8ebe0163655748437ef355a8dc00aaf5f

Verification & scope

A deterministic toy loading model with stipulated constants; it is not an approved aircraft flight manual procedure and makes no claim of regulatory conformance. 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 2026-09-29T14:47:39.115907+00:00.

Case digest / 5e2a73f0366af1d8e7bde81ded90e884e2fc9749b08a827e757a528371951066