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pre-departure clearance problems anlaysts have seen
in recent report submissions to ASRS. ASRS Analysts
took a close look at PDC’s and came up with some
PDC problems and their suggested fixes. The bulletin
begins on page 20.
That’s all for this issue of ASRS Directline. _
Charles Drew—ASRS Directline Executive Editor.
Internet News
ASRS’s web pages have been upgraded. CALLBACK issues and ASRS Directline articles and issues are
now available in “HTML” and Adobe Acrobat versions. A page for ASRS Operational Issues Bulletins has
been added, and we now have mail links to key ASRS staff positions. We are planning to add a number
of ASRS’s research papers in the near future. Finally, the old URL (address) for the ASRS was made a little
simpler (the old address will still work). Access the ASRS at:
http://olias.arc.nasa.gov/asrs
4 Issue Number 9
The incident cited above is one of
many typical altimeter-missetting reports
sent to the Aviation Safety Reporting
System (ASRS). ASRS analysts note
that these reports often come in
bunches, as numerous flight crews experience
the same problem on the same
day in a particular area that is encountering
unusual barometric pressures. Incorrect
altimeter settings are a direct
cause of altitude deviations, some of
them severe enough to result in near
mid-air collisions and controlled flight
toward terrain. Fortunately, most of
these deviations are detected following
an alert from ATC, GPWS, or TCAS, and
are corrected before the situations become
truly perilous.
In this article, we present some of the
common scenarios for altimeter
missetting incidents. In particular, we
focus on incidents associated with the
very low altimeter settings that often
occur during the winter months. We
also consider the influence of human
behavior in altimeter-missetting incidents,
and offer suggestions for pilots to
avoid falling prey to falling barometric
pressure.
Where in the World…?
We searched the ASRS database for
altimeter-missetting
incidents that occurred
during extremely low
barometric pressures,
and found reports from
far and wide. We also
enlisted the aid of the Canadian
Aviation Safety Board, and obtained
some of their reports of incidents and
accidents attributed to misset altimeters.
The greatest number of reports
referenced far-north or very cold
locations—many incidents occurred in
Alaska and in cities near the Great
Lakes. Other locations known for
severe weather and cold temperatures
were also well-represented—New York,
the high-altitude Rocky Mountains,
and parts of Canada. Somewhat
surprisingly, there were also reports
from otherwise relatively temperate
locations, such as San Francisco,
California; Portland, Oregon; Kansas
City, Kansas; and Richmond, Virginia.
Although these areas generally have
less severe weather, unusual frontal
systems created some significant
“This was the last leg of a long 3-day trip…Inbound…we ran the ‘preliminary checklist,’ cross-checking
altimeters at 30.22. This seemed a little odd to me at the time as the area had a low front moving
through, but we were busy and I did not press the issue. Once on approach, everything was normal until just before
the final approach fix when we broke out of the clouds and a ridge was looking very close. Also the GPWS
went off as we passed over the ridge. I checked our altitude and we were right on profile. I had the Captain check
the altimeter with Tower. Altimeter was actually 29.22, not 30.22, putting us approximately 1,000 feet too low
on approach.” (# 292718)
by
Marcia Patten
and
Ed Arri
Issue Number 9 5
changes in barometric pressure and
caught several reporters off-guard.
There were also a number of reports
of incidents that occurred in foreign
locales—Moscow, Keflavik,
Copenhagen, Frankfurt, Brussels.
Many of these locations are even
farther north, that is, at higher latitudes,
than the locations in the
domestic incident reports.
Weather or Not
Weather plays a
significant role in
many incidents
of misset altimeters.
A semipermanent
low
pressure area off the Aleutian Islands
is the perfect set-up to bring frequent
low barometric pressures to Alaska
and Western Canada. Likewise, a winter-
season low that forms between
Greenland and Iceland provides very
low altimeter settings across those
　
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