[Federal Register Volume 59, Number 70 (Tuesday, April 12, 1994)]
[Unknown Section]
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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]
BILLING CODE 4910-13-M