Low Pressure

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OK so I was flying West to East in the winter in my Columbia-400 and the Garmin-1000 winds-aloft page showed 100-knot tailwinds up high. (Real high: 25,000 feet).

So I put on an Oxygen mask and punched all knobs forward with an IFR plan for the climb.
Soon enough I found myself approaching FL250 (25,000 feet).
But here is an interesting thing: The altimeter was an astounding 30.45 inches! That is REALLY high pressure.
In fact, for each inch above standard baro pressure of 29.92, you will actually be flying about one THOUSAND feet higher than indicated!
So, today, with over half an inch of mercury of extra pressure, if someone were to forget to set their altimeter, and just leave it at 29.92, they would actually be flying about FIVE HUNDRED feet too high!
This is because with such a high pressure, they would have to climb an extra five hundred feet to get to the pressure their altimeter expects for any given altitude.
Now, of course, above 18,000 feet in the USA, we are SUPPOSED to “forget” to set our altimeter, and just roll along at a constant pressure altitude with 29.92 in the box… that is standard practice!
SO, that means on this day, flying at FL250 means we are ACTUALLY rolling along at 25,500 feet, since that is how high we have to go to get 25,000 feet worth of pressure.

But wait, there’s more.

Since pressure LAPSE RATES WITH ALTITUDE vary with the weather, aviation needed to come up with a standard lapse rate for all altimeters to use so we would all be flying by the same rule-book when flying a commanded altitude. But, what lapse-rate really is standard, when it varies with the weather? Well, aviation settled on the worst-case scenario, of course, so that if anything, you would be TOO HIGH, NOT TOO LOW, as the pressure lapse-rate varied. In tother words, we err on the side of caution: Following our pressure-based altimeters, we are always a some variable amount HIGHER than we think, but never too low. This helps you crash into mountains less, which is generally regarded as preferable. Those who fly under bridges IFR, at carefully-pre-determined altitudes, are more at-risk with this system, since the extra altitude they wind up carrying carry might cause them to not be UNDER the bridge, but instead right AT the elevation of the roadway, which would be unfortunate as well. The powers-that-be, however, evidently decided that this case was probably going to be less likely, so they designed the lapse-rate that is built into ALL of our altimeters to err on the side of having you actually be a bit HIGHER than planned, not lower, in most of the pressure lapse-rates that we could expect to see here on Earth.

So, how much extra altitude are we really carrying? You can check your GPS altitude from various iPad Apps (including Xavion) to see the answer to that question.

But also I can answer it (from experience looking at GPS versus pressure-based altitudes): at 25,500 feet, you are actually carrying an extra 500 feet.

So, on this day, flying at FL250 was ACTUALLY running me (and everyone else following the rules) at 26,000 feet above the Ocean.

Hmm.

OK.

Sounds pretty boring.

UNTIL you do it in a non-pressurized airplane.

Lured ever-upward by the promise of 200 knots of speed that the Columbia-400 can provide up there, and OVER 100 KNOTS of tailwind, to 26,000 real feet I went.
Pretty soon I got there, and could be said (for a prop plane sipping 16 gallons per hour) to be doing what could technically be referred to as “hauling ass”.

The view out the big windows was pretty awesome: Clouds spread out for maybe a hundred miles in every direction, the clouds far far far below, and the ground visible through the holes far far far below THAT, entire different weather systems visible in different directions, the sky getting all dark and approaching a blackness as you look up, and all that. High-altitude stuff.

Sucking madly on O-2, though, I still felt sort or breathless and dizzy. Was it just me being paranoid?

Pretty soon I noticed that every time Center handed me a new frequency, I tried to contact it and got no reply. I would go back to the previous frequency and find out that the Center controller had in fact given me the wrong frequency. Right? But why were they only doing it NOW? Why were they only doing it when I was feeling breathless and dizzy at 26,000 feet in an un-pressurized airplane? Is this hypoxia? Payne Stewart and his friends all died when their airplane de-pressurized. (FUN FACT: In a lawsuit that resulted form that accident, after hundreds of thousands of dollars of legal fees and expert witnesses and examinations and weeks of trial time, when the testimony was all given, the evidence presented, the arguments all made, and jury sequestered, one woman on the jury submitted a question to the Judge: “When do we found out who won?”. True story. Not a joke. It gets better: EVERYONE on the jury participates in sending questions to the Judge… not a single person on the jury was able to answer that question for the juror. Anyway, if you ever have to count on the justice system in this Country, yer screwed. You just have to watch your OWN back.)

ANYHOO, thinking of Payne Stewart, and that guy recently in the TBM-800 that did the exact same thing (and died) and also that guy in the Cirrus SR-22 that ALSO did the same thing (in the same WEEK!) (and also died), I pondered my wife watching me on FlightAware as my airplane dutifully carried me out well into the Atlantic Ocean, on autopilot, with me unconscious at the wheel (I would also die!) She would NOT like that very much!

So I am up there in a situation that has resulted in many fatalities and I can’t even manage to communicate a simple Center Freq.
Coincidence?
I elected to request a descent.
Challenge points! I could not ask for a lower altitude without tying my tongue and confusing the altitude I was AT for the one I WANTED.

On the second (or third?) try, I got it right, and down I came.

Around 18,000 feet or so (where I usually fly) everything seemed to start making sense again.

So anyhoo, a few lessons there.

Now here is something interesting: Things were a bit sketchy with my O2-conserver apparently being a little stingy with the O2… but that O2-conserver is run by THREE DOUBLE-A BATTERIES!

If those dinky little batteries die? As Seth Meyers says: “YA BURNT!”
If a dinky little O2 hose or connection comes loose? YA BURNT!

In other words, in a non-pressurized plane at that altitude sucking O2, you really could easily be ONE SINGLE FAILURE away from death.
Grab a small battery-powered device, and ask yourself: “Do I want the Death Sentence for letting these batteries die?”
That is actually the sort of the game we are playing here, staying aloft in an unpressurized airplane traveling on Oxygen only.

I try to avoid being one small failure away from a serious accident, so I have sort of decided that wearing a battery-powered O2-conserver in a non-pressurized airplane at high altitude is sort of off-limits, since it does not really follow that rule.

So let’s look at alternatives.

In my Evolution, we probably have a better solution, and here it is:

1: The airplane is, in theory, pressurized. I have to say “In Theory”, because in at least one case that I know of, a window just broke in flight and de-pressurized the plane instantly. In another case I know of, a door latch failed and de-pressurized the plane instantly. Go see the movie INTERSTELLAR. It is awesome. In it, an astronaut that has gone all Cray-Cray tries to dock his lander to a MotherShip and the little latches that grab onto the lander cannot get a good purchase, so when the astronaut opens the door inside the airlock, the pressure from the MotherShip separates the lander and kills everyone. Good if you hate Matt Damon, bad if you are me, since this is how the door-latches on the Evolution work! If they cannot get a proper purchase on the door frame, they are not REALLY locked and sealed, and you cannot (if you are me, anyway) really tell if they have gone over-center and locked. Now, this is something I LOVE about the Epic-LT aircraft: It has a door-latching system that lets you easily confirm is locked, and really does not look like it could fail: It is 8 big huge metal pins driving home deep into wells that are perfectly placed in the airframe to accept the locking pins, and once those pins are in place, that door is not going ANYWHERE. THAT is a door you can bank on. ANYHOO, the Evo is (usually) pressurized which is line-of-defense-number-one against passing out at high altitude and being carried on autopilot to a watery grave over the Atlantic.

2: Also, the Evolution has an emergency Oxygen System that has NO batteries. This is good! It is just like a SCUBA tank: Grab the mask and put it up to your face, and open the little valve on the tank to turn the O2 loose. Opting for functionality over style, I put this tank right between the two front seats on my plane, right under my right hand. I can get to the mask in under 5 seconds, blind-folded, 100% of the time, since it literally sits right under my right hand in flight. So, if the airplane de-pressurizes, we have a nice fall-back. So a backup O2 system is line-of-defense-number-two.

3: Now here is where it gets good, I think. My Evo has a TruTrak autopilot, which will soon be hooked to an iLevil ADS-B receiver. Xavion (an App I wrote) runs on my iPad, which is connected to the iLevil ADS-B receiver by WIFI. I just log my iPad into the iLevil ADS-B receiver WIFI just like I would log into a WIFI at Starbucks (…If I went there anymore. Which I don’t. Because I just recently learned that you can get coffee at places OTHER than Starbucks… places WITHOUT LONG LINES!) So, Xavion logs onto the iLevil WIFI to get weather data. OK stop yawning and bear with me: The iLevil is connected to the TruTrak autopilot with a serial cable! This lets Xavion SEND COMMANDS TO THE AUTOPILOT of the r-Evolution! As well, the iPhone6 has a pressure sensor! This means that if Xavion is running on an iPhone6, it can DETECT a cabin de-pressurization, engage the autopilot, and automatically bring the airplane down to a safe altitude! I tested the system yesterday in an RV-10! (Why no, that airplane is NOT pressurized… which is exactly why the system engaged and took us down when we climbed too high!!!) We set lower auto-descent altitudes and only PRETENDED to fall asleep for obvious safety reasons, but the system works! Youtube video here:

So, the iPhone automatically taking control of the airplane if it de-pressurizes and bringing it down to a safe altitude is line-of-defense-number-three.
This is only in TruTraks’ developmental RV-10 right now, but will go into my r-Evo soon!

So, with the r-Evo with a TruTrak autopilot and an iLevil ADS-B receiver feeding data to a copy of Xavion (www.Xavion.com or find Xavion at the AppStore) has three lines of defense against an oxygen-deprivation accident initiated at altitude. And I guess that is pretty decent. And if you fly an Experimental, then you can get this stuff as well… the TruTrak works with a lot of different planes, and the iLevil ADS-B receiver and Xavion work with all different planes.

You want this:

http://www.trutrakflightsystems.com
http://www.aviation.levil.com

Xavion: Your Plane’s AI Copilot and Instrument Backup

The TruTrak components are in the final stages of testing now, and should be available in the fairly near future!

austin

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