AOPA Pilot Magazine - December 2016 - 81

AIM 8-1-2 (d), "Decompression sickness after scuba diving," states that "a
pilot or passenger who intends to fly after
scuba diving should allow the body sufficient time to rid itself of excess nitrogen
absorbed during diving. If not, decompression sickness due to evolved gas can occur
during exposure to low altitude and create
a serious in-flight emergency." What does
that really mean? How long a wait really
is required?
Divers who go below the surface of the
ocean experience an increase in pressure
of about one atmosphere per 33 feet of
descent. As the pressure increases, divers'
bodies absorb more nitrogen. If the pressure is reduced too quickly, the nitrogen
comes out of solution and forms bubbles in the tissues and blood. Symptoms
of decompression sickness, commonly
called the bends, include skin rashes,
irritable skin, breathing difficulty, joint
and muscle pain, dizziness, vision limitations (even blindness), convulsions, or
unconsciousness.
Guidance on how long to wait before
flying varies. A DiveCompare blogger
notes that "the recommendation set out
by [the Professional Association of Diving
Instructors] is: For single dives, a minimum preflight surface interval of at least
12 hours is recommended. For repetitive
dives, or multiple days of diving, a minimum preflight surface interval of at least
18 hours is recommended. [Divers Alert
Network] recommends 24 hours for repetitive dives, the U.S. Air Force recommends
24 hours after any dive, while the U.S. Navy
tables recommend only two hours before
flying to altitude." The discrepancies
between these agency recommendations
and even the AIM highlight the complexity of the question of how long to wait to fly
after scuba diving.
The AIM says a pilot should wait at
least 12 hours prior to flying to altitudes up
to 8,000 feet msl if a dive has not required a
controlled ascent (nondecompression-stop
diving) and at least 24 hours after diving
in which a controlled ascent (decompression) is required. Any flight above 8,000
feet msl should be delayed until at least 24
hours has elapsed. The AIM says these recommendations are actual flight altitudes

above mean sea level, not pressurized
cabin altitudes-a critical point because of
the concern for any potential loss of aircraft pressurization.
Even if you are not a diver, you may
carry passengers who are. So what are the
basics you should know?
A good practice is to have a "down day"
prior to flight after any diving. Space any
planned flights (even at lower altitudes)
with a day between the last dive and the
flight departure. But as noted, consider
the mean sea level altitude at which flight
will occur, not the 8,000-foot cabin pressure altitude. Many light aircraft will fly
higher, and certainly most cabin-class
business aircraft will fly higher than this
altitude. Two days might be a better plan,
especially if there was deep or repetitive
diving.
Many divers now use computer- or
tablet-based dive-planning software and
underwater dive computers that go with
them when they dive. These dive computers calculate a diver's depth and, in
many cases, oxygen usage; they provide
detailed algorithmic-based computations
that evaluate a diver's activity. Modern dive
computers will calculate a "time to fly" and
recommend a wait time for a diver prior
to a flight.
To be accurate, divers must use the
same computer for all their dives, and on
all the dives. Time-to-fly calculations are
continuously cumulative based on diving times, depths, and numbers of dives.
Whether you are the pilot who dove or
the pilot who will be flying passengers
who were diving, consult the computer
prior to flight or after their last dives are
completed so you are aware of what wait
time is required based on the time-to-fly
calculation.
There is much more you can learn
about diving, effects of pressure, symptoms, and how different activities affect
flight safety. Knowing that the recommended minimums may not be enough can
help you determine if you need more information prior to a flight.
AOPA
JASON BLAIR is a National Association of

Flight Instructors master flight instructor
and a designated pilot examiner.

www.aopa.org/pilot AOPA PILOT | 81

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by Ross Nixon

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asa2fly.com/ﬁndingcarla
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Table of Contents for the Digital Edition of AOPA Pilot Magazine - December 2016
