Weather and airspace

Example 1 Decoding two METAR reports

import re

reports = [
    "METAR VTBD 150100Z 21012G22KT 9999 FEW020 SCT100 30/24 Q1008 NOSIG",
    "METAR VTBD 150700Z 24018G32KT 4000 TSRA FEW015CB BKN030 27/25 Q1006",
]
KT = 0.5144

def decode(r):
    out = {"station": r.split()[1]}
    m = re.search(r"\b(\d{2})(\d{2})(\d{2})Z\b", r)
    out["utc"] = f"day {m.group(1)} {m.group(2)}:{m.group(3)}Z"
    m = re.search(r"\b(\d{3}|VRB)(\d{2,3})(?:G(\d{2,3}))?KT\b", r)
    out["wind"] = f"{m.group(1)} deg {int(m.group(2)) * KT:.1f} m/s" + (f", gust {int(m.group(3)) * KT:.1f} m/s" if m.group(3) else "")
    m = re.search(r"KT (\d{4})\b", r)
    vis = int(m.group(1))
    out["visibility"] = ">= 10 km" if vis == 9999 else f"{vis / 1000:.1f} km"
    out["thunderstorm"] = bool(re.search(r"\bTS|CB\b", r))
    m = re.search(r"\b(M?\d{2})/(M?\d{2})\b", r)
    t, td = (int(x.replace("M", "-")) for x in m.groups())
    out["temp/dew"] = f"{t}/{td} C, spread {t - td} C"
    out["QNH"] = int(re.search(r"\bQ(\d{4})\b", r).group(1))
    return out

for r in reports:
    print(decode(r))

{'station': 'VTBD', 'utc': 'day 15 01:00Z', 'wind': '210 deg 6.2 m/s, gust 11.3 m/s', 'visibility': '>= 10 km', 'thunderstorm': False, 'temp/dew': '30/24 C, spread 6 C', 'QNH': 1008}
{'station': 'VTBD', 'utc': 'day 15 07:00Z', 'wind': '240 deg 9.3 m/s, gust 16.5 m/s', 'visibility': '4.0 km', 'thunderstorm': True, 'temp/dew': '27/25 C, spread 2 C', 'QNH': 1006}

The morning report (08:00 Thai time) has gusts of about 11 m/s and good visibility. The afternoon report (14:00) has a thunderstorm with cumulonimbus, visibility down to 4 km, and only 2 °C between temperature and dew point, which means very humid air. Remember that a METAR is measured at the aerodrome; a site several kilometres away can differ a lot, so use it together with other sources as in Module 1.

Example 2 Checking flight points against the 9 km conditions

A hypothetical aerodrome has its runway midpoint at (0, 0) and runway direction 030/210 degrees. The team treats a 1 km-wide strip along the runway axis out to 9 km as the approach and departure path (the team’s assumption, to be confirmed with the real aerodrome). Coordinates are metres east and north.

import math

RWY_HDG = 30                                   # degrees
CORRIDOR_HALF = 500                            # m, half-width of the approach path (team assumption)
points = {"A": (2500, 900, 40), "B": (1600, 2800, 40), "C": (5600, 3000, 80), "D": (9500, 1000, 110)}   # x, y, height m

u = (math.sin(math.radians(RWY_HDG)), math.cos(math.radians(RWY_HDG)))   # unit vector along the runway
for name, (x, y, alt) in points.items():
    d = math.hypot(x, y)
    across = abs(x * u[1] - y * u[0])          # perpendicular distance from the runway axis
    if d > 9000:
        verdict = f"outside 9 km, general 90 m limit -> {'ok' if alt <= 90 else 'TOO HIGH'}"
    elif d < 1000 or across < CORRIDOR_HALF:
        verdict = "NOT ALLOWED (within 1 km or in approach/departure path)"
    else:
        limit = 45 if d <= 4000 else 90
        verdict = f"needs aerodrome permission, max {limit} m -> {'ok' if alt <= limit else 'TOO HIGH'}"
    print(f"{name}: {d / 1000:.2f} km from runway midpoint, {across:.0f} m off axis, {alt} m -> {verdict}")

A: 2.66 km from runway midpoint, 1715 m off axis, 40 m -> needs aerodrome permission, max 45 m -> ok
B: 3.22 km from runway midpoint, 14 m off axis, 40 m -> NOT ALLOWED (within 1 km or in approach/departure path)
C: 6.35 km from runway midpoint, 3350 m off axis, 80 m -> needs aerodrome permission, max 90 m -> ok
D: 9.55 km from runway midpoint, 7727 m off axis, 110 m -> outside 9 km, general 90 m limit -> TOO HIGH

Point A is far enough from the runway axis but within 1–4 km, so it must stay at or below 45 m. Point B, although only at 40 m, is less than 500 m from the runway axis and so lies in the approach path under the team’s assumption: no flight. Point C is at 4–9 km and may fly up to 90 m with permission. Point D is outside 9 km but still subject to the general conditions, a maximum of 90 m, which the planned 110 m exceeds, so the plan must change.