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Date: Sun, 13 Jan 2013 17:51:42 -0500
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Subject: Re: [LML] Re: LML roots
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From: Ronald STEVENS <Ronald@sdc.com>
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Hi Bill

The only times i am going to the higher flight levels (above 17k) is when I a=
m sure the wind will help me. The 5-10 kts extra is usually not my motivatio=
n. But when I do I have my mask plugged in and ready, specially above 22000 f=
t. Also noticed that the autopilot will starting to 'wander' a little bit so=
 more attention and therefore more anxiety is there. At 17500ft it is usuall=
y above the weather and no chit-chat needed. Can listen to music and enjoy t=
he view. =20

Ronald Stevens IVp, >200 hours


On Jan 13, 2013, at 2:28 AM, Robert R Pastusek <rpastusek@htii.com> wrote:

> Bill Wade wrote:
>=20
> I agree. I've never used an oxygen system before but would like to install=
 an emergency system in the IV-P I'm building. For starters, if there was a r=
apid decompression at altitude how quickly can a system be activated? Mask o=
r cannula- should they be worn around your neck and plugged in just in case?=
 Flow adjustments- I don't know enough yet to even ask intelligent questions=
. Thanks- Bill Wade
>=20
>=20
>=20
> Bill,
>=20
> For the IV-P, I'd recommend that you test/certify the aircraft to no highe=
r than FL 250. The airplane will climb and fly higher, especially if lightly=
 loaded, but the FARs require annual equipment and aircrew checks if it's op=
erated above FL250. The other reason to make this your operational ceiling i=
s that the "time of useful consciousness (TUC) at FL 250 is a couple of minu=
tes under normal situations (several factors/conditions can reduce this sign=
ificantly), but reduces rapidly to seconds as you go higher. Even considerin=
g the reduced TUC from illness, rapid decompression--loss of a window--etc),=
 you have time to get the masks on if you do this as the first action after a=
 de-compression/loss of cabin pressure at FL 250. Above FL 250, a rapid de-c=
ompression is a traumatic/attention -getting event. The most common scenario=
 for IV-P's is loss of a window or part of the door, where the very rapid lo=
ss of pressure will cause you to forcibly exhale, significantly reducing you=
r TUC...above FL 250, this time quickly reduces to seconds. Having experienc=
ed the loss of a canopy in an F-4 many years ago at FL 280, I'm pretty sure m=
y wife would not get back in the airplane if we blew a window or door up the=
re.
>=20
> I mounted my Mountain High (emergency) O2 bottle to the front of the main s=
par box, basically under the front edge of the pilot's seat. Wherever you mo=
unt the bottle, it needs to be in a place you can turn on the main tank valv=
e easily from your pilot seat when needed, AND can check the pressure/quanti=
ty during pre-flight. You'll need a mask that you can slip over your mouth/n=
ose. You'll use this for emergencies only, so a small bottle that supplies 2=
0 minutes of O2 for you and your passengers is more than sufficient. Any of t=
he O2 system suppliers can help you with sizing the pressure bottle to your n=
eeds--be sure they know you have a pressurized cockpit or they will really p=
ress you to buy a more elaborate system. I installed the very simple/basic O=
2 masks from Mountain High in pockets in the sidewall beside the pilot/copil=
ot and each back seat passenger. The front masks are always connected and fl=
ow O2 as soon as the main valve is turned on. The back masks are not normall=
y connected and have shut-off valves in the connectors; I connect them only i=
f taking passengers above 15,000--which is  not normal for me. All masks are=
 very quick and easy to access. Use should be part of your crew/passenger pr=
e-flight briefing if you're taking them above 15,000'. You and your passenge=
rs need to practice donning/activating this equipment with the same commitme=
nt as you practice engine-out landings.  The need for the emergency O2 syste=
m is so infrequent that without practice and conscious thought about it, you=
 won't do the right things, in the right sequence during a rapid decompressi=
on.
>=20
> I'd recommend a cabin pressure sensor connected to a warning light/annunci=
ator or similar instrumentation. Mine is connected to my Electronics Interna=
tional MVP-50 engine/system monitor, and is set to alarm any time the cabin p=
ressure goes above 10,000'. It's performed flawlessly for 5+ years now. (I a=
lso have an identical sensor connected to an outside pressure source that's w=
ired in series with my boost pump so it turns a warning light on if the airp=
lane is above 10,000' and the boost pump is not on. It also lights below 10,=
000' if the boost pump is on... This system is my personal preference...but h=
andy.
>=20
> In the past five years, I've lost cabin pressure twice while at altitude. B=
oth were caused by door seal failures, once the seal itself failed, and once=
 the pump motor failed. Both resulted in fairly rapid loss of cabin pressure=
, but not "explosive decompression" as will occur with loss of a window. Tur=
ning on the O2 and donning masks, then asking for a descent to a lower altit=
ude were "routine" and caused nothing but a bit of anxiety in my co-pilot/wi=
fe.=20
>=20
> One last caution. If you're using the big Continental, its turbochargers w=
ill maintain cabin pressure at/above about 25" of manifold pressure. If you p=
ull the power back below 25" to descend from the flight levels, you'll rapid=
ly dump the cabin pressure back through the engine. I considered installing a=
n "anti-backflow" valve in the system, but then realized that it would only s=
low the loss of cabin pressure a little, as the cabin leaks a good bit (they=
 all do) and need a pretty steady flow of compressed air to maintain pressur=
ization. So I abandoned this idea, and am careful with the throttle on desce=
nts...which is a good engine management practice anyway. The other result of=
 this operating limitation is that you'll need to start down from the flight=
 levels long before you can see your destination...60-90 miles out, dependin=
g on altitude and winds. This takes some getting used to, and speed brakes c=
an help a little. I have them, but almost never use them; it seems such a wa=
ste to burn up the energy/fuel you spend climbing to altitude in aero drag c=
oming back down... My standard/much preferred procedure is to plan a descent=
 well out from destination...you usually have to ask ATC to start down.
>=20
> In summary, you will need only a basic emergency O2 system in your pressur=
ized cockpit. A continuous-flow system with the most basic masks is adequate=
; and don't waste money on pulse flow regulators. I'd also stay away from re=
mote mounting of the bottle, but in any case, do be sure to check the O2 sup=
ply on pre-flight if you plan to go up into the flight levels. I consider th=
e cabin pressure warning system a critical part of my airplane; as important=
 as the AOA system and accurate fuel indicators. All of these are available i=
n relatively inexpensive and reliable instrumentation these days.
>=20
> Write or call if questions/issues.
>=20
> Bob Pastusek
>=20
>=20
>=20
>=20
>=20
>=20
>=20
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