JamesNoBrakes

Depends. Are you using a pulse oximeter and have a reliable alert system for the oxygen system if it fails to flow? If so, I'd be comfortable at 20K, maybe a little higher, but I'd be considering the terrain and where I planned to fly and what my "safe" altitude to descend down to is. If that is 16,000' because I'm going over the rockies and it's IFR, I'm stacking the odds against myself in the case of a single-point failure. If I've chosen a route that minimizes that and has lower MEAs generally, then probably fine, I can dial down the AP in the event of a loss of O2, keeping enough power to remain in level flight when it levels off. I'm not looking to descend "fast" in this case, I'm looking to descend controlled, or at least, that's what I was taught. Assuming this is a piston or turboprop, as a jet would most likely have AT.

AirBear

Like I said we were in the middle of nowhere, WY and only around an hour from destination if that much. If the F/O had wanted to land at the nearest suitable I would have been fine with that despite having Thurston and Lovey in the back. I was not an "A-Teamer", more of a "Catfish Team" kind of guy . There was no love lost between Mx and myself. Granted the F/O wouldn't have made down to a lower altitude conscious if we had a rapid depressurization. The F/O was a very laid back older guy with more hours than me and we did discuss the options and he was like lets not worry about it, silly to divert this close to destination for a possible event neither of us had seen in over 30K hours of combined flying. Top of descent was only about 30 min away. If I hadn't had to use the lav we wouldn't have even known about it. Both mask passed preflight checks. What kind of bothered me was the corrective action was to swap the 2 masks. Then they worked fine. We tested them quite a few times the next couple of legs the following day.

Also, understand that the Phenom was certified under Part 23, not 25. We had no emer heat system that would dump hot bleed air into the jet. With a Rapid Decomp we would have gone from +70F to -70F in a few seconds. Anyone who's had altitude chamber training has seen how fast it cools off when the air is sucked out and that's just sitting on the ground. The physics of why that happens are way over my head but it does. How long do you think pilots can function at -70F with short sleeve shirts on? Your skin will freeze in seconds. That's why we tended to be a bit lax on O2 mask rules on that particular jet.

Of course the only way to get a rapid decomp in a Phenom is to blow a hole in the jet. Limiters slow the loss of pressure way down in the event a outflow valve malfunctions. That's why fighting a hijacker by dumping the cabin wasn't a viable solution since it took so long.

JohnBurke

Oxygen isn't needed only for a depressurization.

You may or may not be cold in a depressurization; it won't matter if the bleed system is dumping hot air into the cabin if there's a structural failure and no way to hold pressurization. You may not be cold, but you'll still die from lack of 02.

I wasn't planning on having the forward windshield depart in flight under pressure, but depart it did. I wasn't planning on a door seal blowing out, but it did. I wasn't planning on a fire, but I've had a few; oxygen isn't just for altitude, and you may need it all the way down.

There's not much that will hurt you faster at altitude than lack of oxygen and lack of pressure.

CaptainYoda

Things to consider:

Pilot cardiovascular health
Pilot proficiency
Overall airplane quality
O2 system quality
O2 monitoring quality

If 2 or 3 of these is in question, stay below 10k


Then consider:
Single Engine -vs- Multi Engine
Terrain
Weather
day -vs- night (remember the effect on night vision)

If you're still not comfortable, or even become uncomfortable enroute, consider lower.
You are your only margin, so you must remain sharp.

JohnBurke

A surprisingly high number of folks ride into the flight levels without ever having experienced a depressurized state at altitude, of a simulation thereof (eg, altitude chamber). Many really have no idea what it feels like to be truly hypoxic and oxygen deprived.

Not only are individual symptoms subjective and specific to the individual, but they can change with time; one may be more susceptible with increased fatigue, smoking, diet, age, caffeine, and other elements, each of which is further complicated by other aspects of high altitude flight.

Know your system, know its limits, its failures, and the implications not just in general, but specific to you.

There was a trend a few years back to fly with a pulse oximeter, which isn't a bad idea, but it can be misleading and unless one has seen the effect in a chamber, and seen how fast 02 blood saturation can crash, one may be overconfident by seeing numbers when all is well. It doesn't take much of a dip to encounter very serious signs and symptoms, and the pressure altitude at which that occurs changes with age, as well as numerous other factors. The altitude one might expect to tolerate today or yesterday might not be the same tomorrow. Be conservative.

Considering the potential for other factors at altitude, indirectly related, one should really pay close attention to what seems trivial on the surface; a minor sinus irritation on the ground might become a sinus implosion on the way down from altitude, and if one hasn't experienced that before (I've been to the ER three times with one), it's a whole new adventure in debilitating pain. As in you may not be able to string two letters together to make a word, even though your 02 sats are fine. I was also deaf for a month in Papua New Guinea, thanks to a rapid depressurization at altitude. It's no joke.

TiredSoul

18’000
1-2 min down to 12,000 in case of a problem. Terrain allowing but you’d have to plan your route accordingly.

rickair7777

Makes sense. But be careful relying on cardio health/fitness. When I had my educational experience, I was in extremely good cardio health and also did military operations above 10K (but always with full-face O2 per mil regs).

But at 14K (for the legal 30 min), while I'm sure my cardio system was happy, my cognitive performance sucked. If we were hiking up a 14K mountain with full gear I would have beat you to the top, but I bet many folks would have flown the plane better than I did. I thought I'd be fine because I was very fit. Turns out there's more to it than that.

I think your acclimation altitude is just as important, probably more important than cardio fitness. If you're already starting at 5K, you'll probably do much better above ten (I was at sea level back then).

There's also individual variability, if you're going to make a habit of that kind of flying, probably want to take a chamber ride to see how you do.

joepilot

One possible solution not mentioned is continuing the flight at a lower altitude. A descent to FL 350 or even 250 would probably leave enough fuel for legal reserves.

The FARs limit a pressurized aircraft to FL 250 if no oxygen is available. There is no regulation for loss of an oxygen system in flight, so it is up to the pilot to choose a safe course of action.

In this case, it appears that the Captain's oxygen system worked OK, so I might have asked the F/O to tighten his shoulder harness and push his seat back a notch so that he would not slump over the yoke if he passed out during a decompression.

Joe

galleycafe

Many aircraft have emergency memory items that call for donning oxygen. No oxygen means unable to comply with a memory item.

Food for thought.

Plane Coffee

HuggyU2

It's been 6 months since the last post, but I want to thank everyone for their input. It is something we are continuing to discuss.

Being an unpressurized aircraft, I believe the best plan is to invest in a backup "bailout" bottle: something that will give at least 10 minutes of 100% oxygen in the event the pilot was beginning to experience hypoxia and/or determine the aircraft's oxygen supply was inop.

Much appreciated.