This forum was started in October 2003 and is distributed weekly to approximately 10 000 email recipients across the globe. Its purpose is to allow the exchange of ideas, tips, and advice for the purpose of aviation safety. Back issues have kindly been made available at http://efc.org.au/_sgt/m3_1.htm . Contributions are encouraged, and welcome.
Diving and Flying
What is Decompression sickness? The simplest explanation remains the so-called SODA STREAM LAW. If we increase gas pressure on any liquid, gas will be dissolved into liquid, directly proportional to the pressure of the gas. Think water in a soda stream machine. If the pressure of the gas is released too fast some of the dissolved gas will come out of solution in the form of bubbles. Think gas bubbles when the pressure is released in the soda stream machine. Releasing the gas in a soda stream bottle is fine but it is not so great if you have nitrogen bubbles flowing around in you arteries and/or veins.
Decompression sickness (DCS) was first studied by scientists in order to establish why bridge and tunnel builders were getting sick and walking stoop (with a bend). They were building inside pressurized chambers called caissons (also called caissons disease). Most of the decompression theories began with the work of Hill and Bert in 1870 and later Haldane in 1908. He observed in his work that you can saturate animals to 2 atmospheres and bring them directly to the surface at 1 atmosphere without any significant bubble formation. This gave birth to the famous Haldane ratio of 2:1. This ratio was later revised to a ratio of 1,58:1.
Further study proved that the body consists of more than one type of tissue i.e. brain, heart, muscles, bones, blood, fatty tissue etc. Each tissue behaves differently under gas pressure, in-gassing and out-gassing at different rates. The rate at which one of these tissue compartments absorbs or eliminates gasses is defined as half-lives. Haldane further suggested stage decompression. The diver would be allowed to go to half the pressure of the previous level and do a decompression stop. This process could be repeated to 1 atmosphere (surface).
Reducing ambient pressure to below that of sea level by ascending in an aircraft after diving can produce DCS. The following rules apply.
p The altitude of an un-pressurized aircraft should not exceed 8000 ft. This is more or less the equivalent of the cabin pressure of a commercial airliner.
p For single dives a minimum preflight surface interval of 12 hours is suggested.
p Decompression, repetitive and/or multiple day dives require a minimum preflight surface interval of 18 to 24 hours.
p Shorter, deeper dives rather than long shallow dives are preferable.
So there you have it. Those chaps that like to fly to Mozambique for a spot of diving, be careful!
FROM THE LOGBOOK:
ARE WE LOSING THE “PURE PILOT”?
ã Jim Trusty
Are
we losing the “pure pilot”? As an
instructor, I vote yes, and every old timer (which is the kindest name we are
called) agrees with me. Airline
jockeys, military pushers, air show performers, test pilots, and scores of
others tell me quite frankly that they would not be where they are today if
their training programs had looked like what we are selling now.
The
inspiration for this article was a discussion with an old Air Force Colonel who
had some great comments about technology and its misuse after reviewing a midair
crash between a couple of biggies.
Our discussion reminded me of a recent good example, a Flight Review and
Instrument Proficiency Check I gave to a young pilot someone referred to me,
either out of hate for the student or an attempt to get my blood pressure
higher.
He was driving a Cessna 172 with a Garmin 430
GPS, Cessna Auto-Pilot, and a WX-10 Weather Head, held a Private Pilot
Certificate and an Instrument Rating and had almost 200 hours. He was very proficient using this panel
and managed to get us to a practice area 25 miles away flying at 2,800 feet and
kicking 90 knots. Upon arrival,
somehow a couple of fuses got loose (me???) and he had to fall back to the VOR,
ADF, compass, pilotage, ded reckoning and the radio. Charts and approach plates were
carefully tucked away in a flight bag (leather) in the rear somewhere, but not
available for us to use. We were
suddenly in a lot of trouble, as he put it, directly over an airport, 2,000 MSL
and doing 75 knots.
This was a sad commentary on the caliber of pilots we
are turning out and backs up the old warhorse theory about too much avionics and
not enough pilot skills. But to
appreciate the whole story, we should now look at both sides of the matter. I have an opinion or two as to how we
can be a little better and safer at what we do. It never hurts to relearn something old
all over again. You may even
recognize yourself or a fellow pilot.
First, the cost of flying has gotten so far out of the
range of most people that we now attract a totally different breed of student
than we did in years past. With the
cost of a trainer at about $75.00 per hour, an instructor at $25.00 plus per
hour, fuel at $2.50, exams,
medicals, checkrides, sunglasses, BIG watch, flight jacket (and suit?), they can
plan on spending in excess of $7,500.00 for a Private Pilot Certificate.
People no longer get a license just to go flying. You must establish long range plans in
order to justify the cost and the time required. No wonder that when they decide to buy
an airplane, they load it up with all the available toys because flying has
become their only diversion from work.
Entertainment, education, vacation, almost everything else that they do
now centers around their plane and the airport. It is a decision they made by choice and
one they are happy with. They are
where they want to be and doing what they want to do . . . with others just like
them!
By
reaching this level of expense, we have taken a whole generation of would-be’s
and put them all in one patch so that we can keep an eye on them. The majority of these folks are business
people who make and spend big bucks.
They waste no time looking out the window for traffic or reading maps to
know where they are and place full dependence on electronic devices that few can
afford and even fewer can set and understand. This is the only segment that can afford
to learn to fly any more and as an instructor, I should be, and am, glad to have
them. They pay the bills and keep
me in the air.
Truthfully, though, I miss the kids. I’ve remained in the same general area
my entire life and manage to see former students and friends almost daily. The struggles we endured together,
scraping together money for the airplane and fuel (and sometimes me), are etched
in our minds. They are needle, ball
and compass pilots who even today can still fly. We won wars with this caliber pilot and
could again if necessary.
Side two of this coin is the constant eroding of pilot
skills as fewer and fewer demands are made of them. I heard that the Air Force is thinking
about using drones as bombers so we would lose fewer pilots, and I wanted to
tell them it appears that we too are working toward that end. With all the electronics made available
to the new pilots of today, I think a drone would be easier, safer and certainly
cheaper.
We
still haul over 600,000,000 passengers each year and the fatalities total about
600, which means we lose one in a million in aviation. No other industry can even come close to
those statistics and they try, so safety is not the number one complaint that I
have. I just come from a different
era, where pilots were smarter than the airplanes, or at least thought they
were, and they could circumnavigate the globe with little or no help from little
flashing machines that involve your looking at them constantly from takeoff to
landing. And I miss that.
I
condone all the panel additions and am constantly amazed at their accuracy. My real complaint is that pilots don’t
use them for what they were designed for�as a backup. They fly them ONLY from point to point
and miss the whole idea of “pure piloting,” the joy, the skill, and the beauty
of flying.
I
see the value in both sides because I don’t have the power to fully control
either completely. Side No. 1 has
come and gone and that generation did the best they could with what was
available. And they did one hell of
a job. I still get to fly with some
of these “old pilots” and it is refreshing. The other side,#2, says we must keep up with other
countries and as all our technology drifts down from the military, we can look
for even more distractions. As a
pilot and flight instructor, I must take the middle ground because on a daily
basis I use and teach both sides.
What’s your opinion? Looked out the window lately? Hand flown a 100 n.m. trip lately? Used the VOR? Shot an NDB approach? Had someone measure the time it takes to
re-set a GPS approach in the air while the airplane flies itself? Now that’s scary! Just remember�do what you do best but do
it safely.
Jim
Trusty