Inspection and records

Example 1 A u-chart for a four-aircraft fleet over one quarter

import math

fleet = {"A": (60, 7), "B": (55, 6), "C": (58, 21), "D": (62, 8)}   # flight hours, defects
UNIT = 10                                                           # hours per unit
ubar = sum(d for _, d in fleet.values()) / (sum(h for h, _ in fleet.values()) / UNIT)
print(f"u-bar {ubar:.2f} defects per {UNIT} h")
for k, (h, d) in fleet.items():
    n = h / UNIT
    u = d / n
    ucl = ubar + 3 * math.sqrt(ubar / n)
    lcl = max(0.0, ubar - 3 * math.sqrt(ubar / n))
    flag = "ABOVE UCL - investigate" if u > ucl else "in control"
    print(f"UAV {k}: u {u:.2f}, limits [{lcl:.2f}, {ucl:.2f}] -> {flag}")

u-bar 1.79 defects per 10 h
UAV A: u 1.17, limits [0.15, 3.42] -> in control
UAV B: u 1.09, limits [0.08, 3.50] -> in control
UAV C: u 3.62, limits [0.12, 3.45] -> ABOVE UCL - investigate
UAV D: u 1.29, limits [0.18, 3.40] -> in control

UAV C is above its upper limit, and not because it flew more than the others. The next step is to break down UAV C’s defects by type; for example, if most are loose screws on the same arm, there may be a crack or a worn mount. Aircraft inside the limits are not necessarily problem-free; they are just not significantly different from the fleet.

Example 2 Checking records for completeness

from datetime import date

REQUIRED = ["uav", "work", "reference", "done_on", "performed_by", "approved_by"]
AUTHORISED = {"Somchai K.", "Nida P."}           # persons authorised to approve return to service per the organisation's manual
records = [
    {"id": "R-101", "uav": "C", "work": "replace arm 2 screws", "reference": "MM 5-3", "done_on": date(2026, 9, 3),
     "performed_by": "Anan T.", "approved_by": "Nida P.", "found_on": date(2026, 9, 2)},
    {"id": "R-102", "uav": "C", "work": "replace motor 2", "reference": "", "done_on": date(2026, 9, 10),
     "performed_by": "Anan T.", "approved_by": "Anan T.", "found_on": date(2026, 9, 9)},
    {"id": "R-103", "uav": "A", "work": "propeller set", "reference": "MM 4-1", "done_on": date(2026, 9, 5),
     "performed_by": "Mali S.", "approved_by": "Somchai K.", "found_on": date(2026, 9, 6)},
]
for r in records:
    problems = [f"missing {f}" for f in REQUIRED if not r.get(f)]
    if r["approved_by"] and r["approved_by"] not in AUTHORISED:
        problems.append(f"{r['approved_by']} is not authorised to approve")
    if r["done_on"] < r["found_on"]:
        problems.append("work completed before the defect was found")
    print(r["id"], "OK" if not problems else "; ".join(problems))

R-101 OK
R-102 missing reference; Anan T. is not authorised to approve
R-103 work completed before the defect was found

Record R-102 has no manual reference, and the technician approved their own work without authority. Record R-103 was completed before the defect was found, which is impossible and probably a typing error. Both must be corrected without deleting the original, by recording the correction with a reason.