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perform concurrent tasks at times,
but it does insure that someone is
flying the airplane and it guards
against both pilots getting pulled
into trying to solve problems. _
End Notes
1 We thank ASRS staff members who
assisted in this study.: Dr. Rowena
Morrison and Mr. Vince Mellone helped
design the search strategy for reports;
Mr. Bob Wright screened reports; Capt.
Bill Richards made callbacks to reporters
and consulted with NASA on selected
incidents; Capt. Charles Drew reviewed
the paper; and Dr. Rowena Morrison
reviewed and edited the paper.
2 Captain Sumwalt is employed by a
major U.S. air carrier, and has served as
an ASRS research consultant since 1993.
He has also published a number of
articles on pilot error and human
factors issues in professional aviation
publications.
3 The relative frequencies of different
types of neglected activity reported
probably do not reflect the relative
frequencies actually occurring in line
operations. Pilots may be more likely to
report incidents observable to ATC, for
example, altitude deviations, than to
report incidents not observable outside
the cockpit, for example, omitting a
checklist item.
4 National Transportation Safety Board
(1994). A review of flightcrew-involved
major accidents of U.S. air carriers, 1978
through 1990. Safety study NTSB/SS-94-
01. Washington, D.C.: NTSB.
10 Issue Number 10
by Jeanne McElhatton, Paul Buchanan, and Charles Drew
A History of Ups and Downs
Throughout 21 years of operation by
the Aviation Safety Reporting System
(ASRS), approximately 35 percent of
all incidents reported to the ASRS have
been altitude deviations. Previous
ASRS reviews of altitude errors have
identified multiple contributing factors
for these events. A 1982 ASRS
study, Probability Distributions of Altitude
Deviations, found that altitude deviations
reported to ASRS were
exponentially distributed with a mean
of 1,080 feet, and that deviations from
ATC-assigned altitudes were equally
likely to occur above or below the assigned
altitude.1 Another ASRS review
of altitude deviation problems, One
Zero Ways to Bust an Altitude,2 looked
at the percentage of altitude deviations
by altitude pairing, (i.e., confusing
one altitude for another) and
found that 35% of all paired deviations
occur at 10,000 and 11,000.
More recently, ASRS analysts have
noted that approximately 15 to 20
percent of the altitude deviations reported
to ASRS involve crossing restriction
errors on Standard
Instrument Departures (SIDs) and
Standard Terminal Arrival Routes
(STARs). SIDs and STARs are published
instrument routings whose primary
purpose is to simplify ATC’s clearance
delivery procedures.
Altitude crossing restrictions associated
with SIDs and STARs may be published
on navigation charts or
assigned by ATC. Crossing restrictions
exist for two primary purposes: 1) to
provide vertical separation from traffic
on different routings that cross the
same fix, and 2) to contain traffic vertically
within a given ATC controller’s
sector in cases where other sectors
within the same facility, or sectors in
another facility, are layered above and
below. ATC-assigned crossing restrictions
(as opposed to published crossing
altitudes) may be temporary requirements
imposed to meet
changing operational conditions, including
facilitating traffic hand-offs to
another sector. Pilot compliance with
SID and STAR altitude assignments is
important, for if a controller permits
traffic penetration of another sector
either laterally or vertically without
prior coordination and approval from
the controller in that sector, an operational
deviation results.
The FMS was programmed for [a] Runway 8 arrival. [The] flight attendant
came forward. I…started reprogramming the FMS for a Runway 26 arrival
and the new crossing restriction. After I had completed this, I noticed that
the FMS was not in VNAV—we had overflown the descent point. I made every
effort but crossed 6,000 feet high.” (# 298266)
“
Crossing Restriction
Altitude Deviations
on SIDs and STARs
Issue Number 10 11
No previous ASRS review of SIDand
STAR-related altitude deviations
has been conducted. Thus we undertook
this review to determine the
causes and contributors to altitude deviations
that occur during SID and
STAR procedures, and to compare the
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