Figure: GV Automatic Emergency Descent, from GV Aircraft Operating Manual, §06-04-00, figure 1.

Eddie Sez:

I've had one rapid depressurization over the years — at FL 350 in a Boeing 707 — and believe all the practice in the simulator you can get comes in handy. There are a few things most of us pilots don't understand about the requirements, the priorities, and the process. A better understanding could save your life.

  • Requirements: most of us believe the regulations mandate we be able to get the airplane from any cruise altitude to 10,000' in four minutes or less. There is no such requirement. 14 CFR §121.333 and 14 CFR 135.157 stipulate oxygen requirements that become stricter if a descent to 14,000' (121) or 15,000' (135) cannot be made in 4 minutes.

  • Priorities: The G450 will get the aircraft headed downhill for you, even if you do nothing. Your priority is to get on oxygen. Take a look at the case of Learjet N47BA for what happens when you don't.

  • Process: The first thing you as the pilot need to do is breathe. Rather than fumble with your glasses, headset, or that filet mignon sitting in your lap, pull out the oxygen and put the mask to your face. Take a few breaths, dial the altitude select knob down, ensure the airplane enters a dive. Then, calmly, takeoff your glasses and headset, place the oxygen mask over your head, and get on with the business of saving everyone's lives.

Notice a recurring theme? Don't believe those times of useful consciousness charts, you are not going to last that long. Read Abnormal Procedures / Rapid Depressurization to find out why.

What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.


Manual Rapid Descent Procedure

[G450 Airplane Flight Manual, §04-21-20]


Automatic Emergency Descent

[G450 Airplane Flight Manual, §04-21-30] The autopilot has an automatic Emergency Descent Mode (EDM) that is armed anytime aircraft altitude is greater than 40,000 feet with autopilot selected ON. When the red Cabin Pressure Low warning message is displayed on the Crew Alerting System (CAS) and aircraft altitude is greater than 40,000 feet with autopilot selected ON, the following occurs:

NOTE: The pilot may override EDM by disconnecting the autopilot.

You should leave the autopilot engaged and use the touch control steering (TCS) to get the airplane pointed where you wanted — if you pass out the autopilot can get you down to altitude, level off, and push the power levers forward. Even if the speed brakes are deployed, the aircraft will maintain speed until you recover.


Oxygen Duration vs Descent Target

Figure: G450 Oxygen duration chart, from G450 Airplane Flight Manual, §01-35-00, figure 1.

How low do you go? Well, how much oxygen do you have? The G450 oxygen chart in the AFM Limitations section only provides crew duration, on the theory that you will get down to 15,000' where the passengers can - legally - go off oxygen:

Figure: Oxygen durations, from G450 Operating Manual Supplement G450-OMS-02, Table III.

But if you want to know the right answer, you will have to look at the Operating Manual Supplement OMS 2, Extended Range Operations, where you will find this gem:


References

14 CFR 121, Title 14: Aeronautics and Space, Operating Requirements: Domestic, Flag, and Supplemental Operations, Federal Aviation Administration, Department of Transportation

14 CFR 135, Title 14: Aeronautics and Space, Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons on Board Such Aircraft, Federal Aviation Administration, Department of Transportation

FSI G450 PTM, FlightSafety International Gulfstream G450 Pilot Training Manual, Volume 2, Aircraft Systems, October 2008

FSI G450 MTM, FlightSafety International Gulfstream G450 Maintenance Training Manual, August 2008

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Airplane Flight Manual, Revision 36, December 5, 2013

Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013

Gulfstream G450 Operating Manual Supplement, G-450-OMS-02, Extended Operations (ETOPS) Guide, Revision 2, April 2, 2009

Gulfstream G450 Wiring Diagram Manual, Revision 17, October 31, 2012