Gulfstream G550 · N688CB
Altitude profile · flown vs. floor
Plan view · the three areas & the track flown
What happened
On a departure to Athens Eleftherios Venizelos International Airport (ATH), N688CB crossed into the noise-abatement area over Yio Chu Kang (Area 2), where the published floor is 1,500 ft, and descended to a QNH-corrected 1,385 ft — 115 ft below the floor.
In-area minimum
1,385 ft corrected, over Yio Chu Kang.
Rule
Yio Chu Kang · 1,500 ft floor. A hard performance gate — no landing exemption.
Why these altitudes are trustworthy
ADS-B broadcasts pressure altitude against a standard datum. We re-reference every value to the day's actual sea-level pressure — the QNH of 1009 hPa — so the figures match what a pilot reads on the altimeter.
How sure we are
The 115 ft gap is well beyond the combined ADS-B + QNH measurement margin, so the aircraft was below the minimum beyond any measurement doubt — this is asserted, not provisional. Readings within the margin are held back and never published here.
What we can't see. Public data does not show an ATC descent clearance or rule out a genuine emergency. There is no landing exemption here, and medical-evacuation status — a curfew-only exemption — does not apply to the noise-abatement floors. We publish the measurement and the caveat together. Flew a medevac, diversion or emergency, or spotted an error? Declare an exemption or correction →