Emergency Descent & Depressurisation
advancedUS phraseologyA rapid depressurisation at cruise forces an immediate emergency descent. Make the MAYDAY, squawk 7700, broadcast the descent to surrounding traffic, and read back the assigned level and altimeter while requesting the nearest suitable airport — with full airline callsign discipline throughout.
Briefing
You are in the cruise at FL370 in Boeing 777 Speedbird two four five, working Denver Center on 134.550. A rapid cabin depressurisation occurs. Oxygen masks are on and you are initiating a memory-item emergency descent.
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- Exchange 1
Masks on, descent initiated. Make the MAYDAY to Denver Center: MAYDAY three times, callsign, emergency descent, and that you are squawking seven seven zero zero.
💡 A rapid depressurisation is a distress — MAYDAY, not PAN. Squawk 7700 alerts every ATC unit even before you speak, and stating "emergency descent" plus leaving level gives the controller what they need to clear the airspace beneath you.
- Exchange 2
You are descending through busy airway levels and may not have positive separation. Broadcast the emergency descent to all stations / surrounding traffic.
💡 An emergency descent can take you rapidly through other aircraft's levels. A general "all stations" broadcast of your descent and level warns nearby traffic directly, backing up ATC — repeat the key words so a partially-blocked transmission still carries the warning.
- Exchange 3
ATC: “Speedbird two four five, Denver Center, roger MAYDAY, descend and maintain one zero thousand, altimeter three zero zero one, say intentions.”
Read back the assigned altitude and altimeter, then request vectors to the nearest suitable airport. Altitude and altimeter are mandatory readback items.
💡 Even in an emergency the altitude and altimeter setting are mandatory readbacks — they keep you separated from terrain and traffic once you level off. Airline callsigns are never abbreviated: it stays "Speedbird two four five" throughout.
Background reading
- GuideMastering VNAV Descent: Stop Arriving Too High and Too Fast
How VNAV descent works in the PMDG 737 and Airbus A320 — PATH vs SPD, managed descent, altitude constraints, and how to recover when you're too high.
- GuideWhy VNAV Doesn't Work When You Turn On the Autopilot
VNAV won't engage or won't descend in MSFS 2024? The 6 most common causes on the PMDG 737 and Airbus A320 — and exactly how to fix each one.
- GuideFenix A320 Failure Training: Master the 4 Emergencies Every Sim Pilot Should Practice
Practice engine failure, engine fire, rapid decompression and unreliable airspeed in the Fenix A320 — step-by-step ECAM drills and how to stay calm.