⚡ Median line crossings: central, southwestern and eastern airspace (3 sorties)
SITREP · Sep 21
4
PLA Sorties
▼1
3
Median Line Crossings 75%
11
PLA Vessels
▼6
▲▼ compared with the previous day
44/100
Normal
Routine activity at everyday scale
▼ below the 7-day average (-20)
Index components
PLA sorties4sorties33×0.35
Median-line crossings3sorties30×0.35
PLA vessels11vessels70×0.20
Active airspaces3zones75×0.10
Last 60 published daysPeak 87Mean 44Dashed = dark-theme threshold 66
This site's own composite of the MND's published figures — not an official alert level.
September MTD · 20 days
179
PLA Sorties
114
Median Line Crossings 64%
10.8
Avg Vessels/Day
Activity AreasTaiwan Strait · Indicative
12 NM territorial sea (green) is the de facto legal boundary. PLA aircraft/vessels crossing the median line does not trigger the right of self-defense; entry into the territorial sea or airspace within this boundary would, under international law and the Defense Act, allow Taiwan to take defensive action.
On Sep 21, 2026, 4 PLA aircraft sorties were detected, of which 3 crossed the Taiwan Strait median line (75% crossing rate); 11 PLA naval vessels.
Last 14 daysToday: 4 sorties · 3 crossed11 vessels
Crossed median lineDid not cross30-day avg 6.4Vessels
2026 YTDMonth peak: 28 (Sep 18)Vessels 2–20