[Federal Register Volume 59, Number 70 (Tuesday, April 12, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-8775]
[[Page Unknown]]
[Federal Register: April 12, 1994]
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Part IV
Department of Transportation
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Federal Aviation Administration
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14 CFR Part 91
Temporary Restriction of Instrument Approaches and Certain Visual
Flight Rules Operations in High Barometric Weather Conditions; Final
Rule
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14 CFR Part 91
[Docket No. 26806; Amdt. 91-240]
RIN 2120-AD75
Temporary Restriction of Instrument Approaches and Certain Visual
Flight Rules Operations in High Barometric Weather Conditions
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
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SUMMARY: This final rule amends part 91 of the Federal Aviation
Regulations (FAR) to provide for the issuance of temporary flight
restrictions on certain operations when accurate altitude information
is not available. The rule is warranted because barometric pressure
higher than 31.00 inches of mercury (inHg) (1049.8 millibars) exceeds
the capability of standard aircraft pressure altimeters and prevents
the display of accurate altitude information. The rule provides
restrictions on certain flight operations during periods of abnormal
atmospheric pressure conditions and is necessary to promote flight
safety during certain operations for which accurate altitude
information is critical.
EFFECTIVE DATE: May 12, 1994.
FOR FURTHER INFORMATION CONTACT:
Mr. Larry Youngblut, Regulations Branch (AFS-240), Flight Standards
Service, Federal Aviation Administration, 800 Independence Avenue, SW.,
Washington, D.C. 20591, Telephone: (202) 267-3755.
SUPPLEMENTARY INFORMATION:
Background
For several days in January 1989, weather observers in various
locations in the State of Alaska recorded record-breaking barometric
pressure higher than 31.00 inHg (1049.8 millibars). These extremely
high barometric pressures exceeded the capability of standard aircraft
pressure altimeters and prevented the display of accurate altitude
information on aircraft pressure altimeters. This condition
occasionally extends to northern portions of the contiguous United
States.
Aircraft altimeters indicate altitude based on a reading of the air
pressure surrounding the aircraft. These altimeters incorporate an
adjustment for environmental barometric pressure that permits pilots
manually to set the correct pressure reading in the instrument. If the
pressure setting is incorrect, the altitude readout also will be
incorrect. Because barometric readings of 31.00 inHg, or higher, seldom
occur, standard altimeters do not permit barometric pressures to be set
above that level and are not calibrated to indicate accurate aircraft
altitude when the surface pressure exceeds 31.00 inHg. As a result,
many altimeters cannot be set to display accurate altitude readouts to
pilots in conditions such as those that were experienced during the
high pressure conditions in Alaska.
It is possible to estimate the error in altitude for pressures
above 31.00 inHg by adding 100 feet in aircraft altitude for each .10
inHg. However, significant recurring training would be required to
ensure all pilots correctly apply the appropriate correction during the
appropriate phase of flight. If two pilots flying aircraft in the same
vicinity are not applying the same correction, a highly dangerous
situation is created when they are at the same altitude although they
believe they are at different altitudes relative to each other.
Accurate altitude information is essential for normal flight
operations and critical to certain phases of flight. Without an
accurate altitude reading, a pilot cannot safely execute an instrument
approach in instrument weather conditions unless certain restrictions
are followed.
Proposed Rulemaking and Discussion of Comments
On March 12, 1992, the FAA published a notice of proposed
rulemaking (NPRM) inviting all persons to submit written comments on
the proposed amendment to Sec. 91.92 of the Federal Aviation
Regulations (FAR) (57 FR 8830). The FAA received comments to the NPRM
from the Air Traffic Control Association, the Air Transport Association
(ATA), the Airline Pilots Association, KLM Royal Dutch Airlines (KLM),
and the Canadian Airline Pilots Association (CALPA). All five
commenters responded favorably to the amendment; however, the ATA, KLM,
and CALPA had additional comments.
ATA requested, for purposes of clarification, that the final rule
state that the restrictions are to be applied in any region when the
barometric pressure exceeds 31.00 inHg. The FAA disagrees that the
suggested additional language is needed. The application of this rule
is not intended to be limited to any geographical area, and discussion
of regions may lead to confusion concerning the rule's applicability.
The final rule clearly states the rule is applicable to any route of
flight.
KLM Royal Dutch Airlines (KLM) suggested that a note addressing the
Outer Marker (OM) crossing altitude as published on the applicable
instrument approach procedure be added either to the rule or as part of
the NOTAM implementing the rule. It argued that very low temperatures
require an increase of the published (standard atmosphere) crossing
altitude, while extremely high barometric pressures would call for a
decrease in the crossing altitude and that, in most cases, both effects
would cancel out each other. KLM stated, however, that if flight
crewmembers only increased the crossing altitude for temperature, as is
the normal procedure, an incorrect crossing altitude would be computed
that would not provide an accurate check for intercepting the
instrument landing system (ILS) glidepath.
The FAA agrees with KLM that extremely cold temperatures and high
barometric pressures, which usually accompany one another, normally
cancel out the effects of each other in altitude computations. The FAA
does not believe, however, that a note concerning this phenomenon is
appropriate for the FAR. An appropriate note might be included in the
Airman's Information Manual (AIM). CALPA also commented that the NPRM
contained no reference to corrections for extremely cold air
temperatures. It stated that Canadian airline procedure compensates for
lower than normal ambient temperatures. CALPA suggested adding to the
final rule instrument approach procedures that contain tabulations
allowing the pilot to make corrections when very cold temperatures are
experienced.
The FAA is aware of the Canadian procedures on altimetry and
recently completed a study entitled ``Extreme Cold Weather Altimetry.''
At this time, however, the FAA has not developed any procedures as a
result of the study. The FAA will amend the rule should procedures
formulated from this study dictate an amendment.
Temporary Restrictions on Flight Operations
On the basis of the above discussion, the FAA finds that the
occurrence of abnormally high barometric pressure conditions creates an
operational situation that requires immediate action to maintain safety
of flight in the affected areas. It is necessary for the FAA to issue
temporary restrictions on certain instrument flight rules (IFR)
approaches and visual flight rules (VFR) operations while extreme
weather conditions exist.
The specific restrictions authorized by this rule will be issued in
a Notice to Airmen (NOTAM) by each affected FAA region when any
information indicates the barometric pressure will exceed 31.00 inHg.
Paragraph 7-531 of the FAA Airman's Information Manual contains the
procedures that will be put into effect by NOTAM when the pressure is
above 31.00 inHg.
These restrictions may include, but are not limited to, the
following:
1. All aircraft: Set the altimeter to 31.00 inHg for en route
operations below 18,000 feet mean sea level (MSL). Maintain this
setting until the aircraft is beyond the affected area or until
reaching the final approach segment. At the beginning of the final
approach segment, set the altimeter to the current barometric pressure,
if possible. If not possible, leave the altimeter set at 31.00 inHg
throughout the approach. Altimeters on departing aircraft or on
aircraft on missed approach will be set to 31.00 inHg before the
aircraft reaches any mandatory/crossing altitude, or 1,500 feet above
ground level (AGL), whichever is lower.
2. During preflight, altimeters shall be checked, to the extent
possible, for normal operation.
3. If the aircraft is being operated into or out of airports with
the capability of measuring the current barometric pressure and the
aircraft is equipped with an altimeter that has the capability to be
set to the current barometric pressure, no additional restrictions
apply.
4. For aircraft operating under VFR, there are no additional
restrictions; however, extra diligence is essential in flight planning.
5. Airports without the capability for accurate measurement of
barometric pressures above 31.00 inHg will report the barometric
pressure as ``in excess of 31.00 inHg.'' Flight operations to and from
those airports are restricted to VFR weather conditions.
6. For aircraft operating under IFR and equipped with an altimeter
that does not have the capacity to be set at the current barometric
pressure, the following restrictions apply:
a. To determine the suitability of takeoff airports, destination
airports, and alternate airports, increase ceiling requirements by 100
feet and visibility requirements by \1/4\ mile for each .10 inHg of
pressure, or any portion thereof, over 31.00 inHg. These adjusted
values are to be applied in accordance with the requirements of the
applicable operating regulations and operations specifications.
b. On approach, 31.00 inHg will remain set on the altimeter.
Decision height or minimum descent altitude shall be deemed to have
been reached when the published minimum altitude is displayed on the
altimeter.
c. These restrictions do not apply to authorized Category II and
Category III ILS operations, nor do they apply to certificate holders
using approved QFE (absolute altitude) altimetry systems.
7. The Regional Flight Standards Division manager of the affected
area is authorized to approve temporary waivers to permit emergency
resupply or emergency medical services operations.
The NOTAM issuing the temporary restrictions will incorporate a
reference to the rule.
Paperwork Reduction Act
In accordance with the Paperwork Reduction Act of 1980 (Pub. L. 96-
511), there are no requirements for information collection associated
with this rule.
Regulatory Evaluation Summary
The FAA has determined that this rulemaking is not ``significant''
as defined by Executive Order 12866. Therefore, no Regulatory Impact
Analysis is required. Nevertheless, in accordance with Department of
Transportation policies and procedures, the FAA has evaluated the
anticipated costs and benefits, which are summarized below. For more
detailed economic information, see the full regulatory evaluation
contained in the docket.
The rule involves additional costs to aviators through delays in
flying to airports experiencing extremely high barometric pressure. The
cost of the rule varies by the number of hours of delay, by the level
of activity at the restricted airports, and by the type of aircraft
delayed. Data from the National Weather Service (NWS) was used to
estimate the amount of time airports will experience extreme high
pressure. The discounted 10 year cost of this rule due to delays
resulting from the restrictions is estimated to be $3.0 million.
Benefits of the rule are avoidance of midair collisions during
periods of extremely high barometric pressure. These meteorological
conditions increase the risk of midair collision resulting from the
inconsistency of altitude measurement.
Although the FAA searched and did not find any midair collisions
occurring under high barometric pressure, the combination of low
visibility conditions, such as at night or in fog, and lack of
consistent altitude measurement increases the risk for all aircraft in
the airspace system under high barometric conditions. The rule will
reduce that risk during such weather conditions by establishing uniform
procedures to reduce confusion and to prevent inadequately equipped
aircraft from flying into these conditions.
Pilots always risk a midair collision in busy airspace, and high
barometric pressure heightens that risk. In Alaska, the FAA recorded 28
near midair collisions from 1987 through 1989. Although the FAA cannot
precisely quantify the increase in risk, it is apparent that the risk
of midair collisions increases substantially when pilots do not know
their precise altitude as under high barometric pressure. Additionally,
the FAA estimates that the number of aircraft flying in such conditions
will increase by 30 percent over the next 10 years. The combination of
increased risk due to high barometric pressure and a nearly one-third
increase in aircraft operating under these conditions makes a midair
collision much more likely. Without restrictions under high barometric
conditions, there is a potential for at least one midair collision. The
discounted value of avoiding just one midair collision over the next 10
years is $5.0 million.
The FAA estimates the discounted 10-year cost of the rule to be
$3.0 million. This cost is the highest possible cost assuming that all
landings during extremely high barometric pressure are restricted.
Aircraft with more sophisticated avionics will be able to land even
with restrictions in effect. Also, aircraft could land under VFR
conditions. The benefit of avoiding just one midair collision over the
next ten years has a discounted value of $5.0 million, greater than the
estimated cost of the rule during that period.
International Trade Impact Analysis
All foreign and domestic aircraft would be equally affected by this
rule. Hence, this rule will have no effect on the sale of foreign
aviation products or services in the United States. The rule also does
not affect the sale of United States products of services in foreign
countries.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) ensures that
government regulations do not needlessly and disproportionately burden
small businesses. The RFA requires FAA to review each rule that may
have a ``significant economic impact on a substantial number of small
entities.''
The FAA criteria set ``a substantial number'' as not less than 11
and at least one-third of the small entities subject to the rule. Among
air carriers, a small entity is defined as one that owns, but does not
necessarily operate, 9 or fewer aircraft. The criteria set ``a
significant economic impact'' as follows: $101,988 for scheduled air
carriers with 60 or more seats; $57,011 for scheduled air carriers with
fewer than 60 seats; and $4,011 for unscheduled operators.
It is possible that in certain cases the cost of delays to small
entities might exceed the threshold. However, the number of small
entities that this rule might affect is difficult to estimate. At any
rate, only those small entities in Alaska are likely to be affected by
the rule since almost all extremely high pressure occurrences take
place in Alaska. Of the 77 part 135 commuters with 9 or fewer aircraft
in the United States, 15 (or 19 percent) are located in Alaska. In the
case of unscheduled part 135 operators (air taxis) with 9 or fewer
aircraft, only 6 percent of the 2,634 such operators in the United
States operate in Alaska. In each instance, the proportion of small
entities exposed to costs under the rule is considerably less than one-
third.
Thus, the FAA determines that the rule will not have a significant
economic impact on a substantial number of small entities.
Federalism Implications
The regulation herein will not have substantial direct effects on
the States, on the relationship between the national government and the
States, or on the distribution of power and responsibilities among the
various levels of government. Therefore, in accordance with Executive
Order 12612, it is determined that this rule will not have sufficient
federalism implications to warrant the preparation of a Federalism
Assessment.
Conclusion
For the reasons discussed in the preamble, the FAA has determined
that this regulation is not significant under Executive Order 12866. In
addition, the FAA certifies that this regulation will not have a
significant economic impact, positive or negative, on a substantial
number of small entities under the criteria of the Regulatory
Flexibility Act. The regulations is not considered significant under
DOT Regulatory Policies and Procedures (44 FR 11034; February 26,
1979). A regulatory evaluation, including a Regulatory Flexibility
Determination and Trade Impact Analysis, has been placed in the docket.
A copy may be obtained by contacting the person identified under FOR
FURTHER INFORMATION CONTACT.
List of Subjects in 14 CFR Part 91
Aviation safety, Instrument flight rules, Special visual flight
rules, Visual flight rules.
The Amendment
In consideration of the foregoing, the Federal Aviation
Administration amends part 91 of the Federal Aviation Regulations (14
CFR part 91) as follows:
1. The authority citation for part 91 continues to read as follows:
Authority: 49 U.S.C. app. 1301(7), 1303, 1344, 1348, 1352
through 1355, 1401, 1421 through 1431, 1471, 1472, 1502, 1510, 1522,
and 2121 through 2125; articles 12, 29, 31, and 32(a) of the
Convention on International Civil Aviation (61 Stat. 1180); 42
U.S.C. 4321 et seq: E.O. 11514, 35 FR 4247, 3 CFR, 1966-1970 Comp.,
p. 902; 49 U.S.C. 106(g).
2. Section 91.92 is added to read as follows:
Sec. 91.92 Temporary Restriction on Flight Operations During
Abnormally High Barometric Pressure Conditions.
(a) Special flight restrictions. When any information indicates
that barometric pressure on the route of flight currently exceeds or
will exceed 31 inches of mercury, no person may operate an aircraft or
initiate a flight contrary to the requirements established by the
Administrator and published in a Notice to Airmen issued under this
section.
(b) Waivers. The Administrator is authorized to waive any
restriction issued under paragraph (a) of this section to permit
emergency supply, transport, or medical services to be delivered to
isolated communities, where the operation can be conducted with an
acceptable level of safety.
Issued In Washington, DC., on April 6, 1994.
David R. Hinson,
Administrator.
[FR Doc. 94-8775 Filed 4-11-94; 8:45 am]
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