AIM
4/20/23
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9
Potential Flight Hazards
f.
The FAA recommends that seaplane owners and operators obtain Advisory Circular (AC) 91
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69, Seaplane
Safety for 14 CFR Part 91 Operations, free from the U.S. Department of Transportation, Subsequent Distribution
Office, SVC
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121.23, Ardmore East Business Center, 3341 Q 75
th
Avenue, Landover, MD 20785; fax: (301)
386
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5394. The USCG Navigation Rules International
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Inland (COMDTINSTM 16672.2B) is available for a fee
from the Government Publishing Office by facsimile request to (202) 512
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2250, and can be ordered using
Mastercard or Visa.
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10. Flight Operations in Volcanic Ash
a.
Severe volcanic eruptions which send ash and sulphur dioxide (SO
2
) gas
into the upper atmosphere occur
somewhere around the world several times each year. Flying into a volcanic ash cloud can be exceedingly
dangerous. A B747
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200 lost all four engines after such an encounter and a B747
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400 had the same nearly
catastrophic experience. Piston
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powered aircraft are less likely to lose power but severe damage is almost certain
to ensue after an encounter with a volcanic ash cloud which is only a few hours old.
b.
Most important is to avoid any encounter with volcanic ash. The ash plume may not be visible, especially
in instrument conditions or at night; and even if visible, it is difficult to distinguish visually between an ash cloud
and an ordinary weather cloud. Volcanic ash clouds are not displayed on airborne or ATC radar. The pilot must
rely on reports from air traffic controllers and other pilots to determine the location of the ash cloud and use that
information to remain well clear of the area. Additionally, the presence of a sulphur-like odor throughout the
cabin may indicate the presence of SO
2
emitted by volcanic activity, but may or may not indicate the presence
of volcanic ash. Every attempt should be made to remain on the upwind side of the volcano.
c.
It is recommended that pilots encountering an ash cloud should immediately reduce thrust to idle (altitude
permitting), and reverse course in order to escape from the cloud. Ash clouds may extend for hundreds of miles
and pilots should not attempt to fly through or climb out of the cloud. In addition, the following procedures are
recommended:
1.
Disengage the autothrottle if engaged. This will prevent the autothrottle from increasing engine thrust;
2.
Turn on continuous ignition;
3.
Turn on all accessory airbleeds including all air conditioning packs, nacelles, and wing anti-ice. This will
provide an additional engine stall margin by reducing engine pressure.
d.
The following has been reported by flightcrews who have experienced encounters with volcanic dust
clouds:
1.
Smoke or dust appearing in the cockpit.
2.
An acrid odor similar to electrical smoke.
3.
Multiple engine malfunctions, such as compressor stalls, increasing EGT, torching from tailpipe, and
flameouts.
4.
At night, St. Elmo’s fire or other static discharges accompanied by a bright orange glow in the engine
inlets.
5.
A fire warning in the forward cargo area.
e.
It may become necessary to shut down and then restart engines to prevent exceeding EGT limits. Volcanic
ash may block the pitot system and result in unreliable airspeed indications.
f.
If you see a volcanic eruption and have not been previously notified of it, you may have been the first person
to observe it. In this case, immediately contact ATC and alert them to the existence of the eruption. If possible,
use the Volcanic Activity Reporting form (VAR) depicted in Appendix 2 of this manual. Items 1 through 8 of
the VAR should be transmitted immediately. The information requested in items 9 through 16 should be passed
after landing. If a VAR form is not immediately available, relay enough information to identify the position and
nature of the volcanic activity. Do not become unnecessarily alarmed if there is merely steam or very low-level
eruptions of ash.