[Federal Register Volume 61, Number 101 (Thursday, May 23, 1996)]
[Proposed Rules]
[Pages 26036-26040]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-13030]




[[Page 26035]]


_______________________________________________________________________

Part V





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



_______________________________________________________________________



14 CFR Parts 121 and 135



Air Traffic Control Radar Beacon System and Mode S Transponder 
Requirements in the National Airspace System; Proposed Rules

  Federal Register /Vol. 61, No. 101/ Thursday, May 23, 1996/ Proposed 
Rules  

[[Page 26036]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 121 and 135

[Docket No. 28586; Notice No. 96-5]
RIN 2120-AE81


Air Traffic Control Radar Beacon System and Mode S Transponder 
Requirements in the National Airspace System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: This notice proposes to rescind the Mode S transponder 
requirement for all aircraft operations under part 135 and certain 
aircraft operations under part 121 of the Federal Aviation Regulations 
(14 CFR parts 121 and 135). For part 121 operators, this amendment 
would affect only those aircraft not required to have Traffic Alert and 
Collision Avoidance System II (TCAS II). The initial mandate for Mode S 
equipage was based on the assumption that Mode S would provide the sole 
method for air traffic control data link. The FAA's revised strategy of 
multiple air-ground data links managed through an Aeronautical 
Telecommunications net work removes this requirement. Further, 
operational experience with the Mode S ground sensors has shown that 
most surveillance enhancements can be achieved by the Mode S ground 
sensors with the present mixed population of airborne transponders. In 
addition, the use of Mode S transponders for aircraft, other than those 
required to have TCAS II, does not offer, nor is it expected to offer, 
any significant safety advantage in the current or future airspace 
environment. Therefore, requiring all aircraft at this time to have 
Mode S transponders when those aircraft are not required to have TCAS 
II is not essential for a safe and efficient National Airspace System. 
In the current airspace operational environment, the public interest 
does not require that all transponders newly installed in certain 
aircraft operated under part 121 and all aircraft operated under part 
135 after January 1, 1992, be Mode S transponders.

DATES: Comments must be received on or before July 22, 1996.

ADDRESSES: Comments on this NPRM should be mailed, in triplicate to: 
Federal Aviation Administration, Office of the Chief Counsel, 
Attention: Rules Docket (AGC-200), Docket No. 28537, 800 Independence 
Avenue, SW., Washington, DC 20591. Comments may also be sent 
electronically to the Rules Docket by using the following Internet 
address: [email protected]. Comments must be marked Docket No. 
28586. Comments may be examined in the Rules Docket in Room 915G on 
weekdays between 8:30 a.m. and 5 p.m., except on Federal holidays.

FOR FURTHER INFORMATION CONTACT: Mr. Daniel V. Meier Jr., Air Carrier 
Operations Branch (AFS-220), Air Transportation Division, Federal 
Aviation Administration, 800 Independence Avenue SW., Washington, DC 
20591; telephone (202) 267-3749.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Any person may obtain a copy of this NPRM by submitting a request 
to the Federal Aviation Administration, Office of Rulemaking, 800 
Independence Avenue SW., Washington, DC 20591, or by calling (202) 267-
9677. Communications must identify the notice number of this NPRM. 
Persons interested in being placed on a mailing list for future FAA 
NPRM's should request a copy of Advisory Circular No. 11-2A, Notice of 
Proposed Rulemaking Distribution System, which describes application 
procedures.
    An electronic copy of this document may be downloaded using a modem 
and suitable communications software from the FAA regulations section 
of the Fedworld electronic bulletin board service (telephone: 703-321-
3339) or the Federal Register's electronic bulletin board service 
(telephone 202-512-1661). Internet users may reach the FAA's web page 
at http://www.faa.gov or the Federal Register's webpage at http://
www.access.gpo.gov/su__docs for access to recently published rulemaking 
documents.

Availability of NPRM's

    Any person may obtain a copy of this NRM by submitting a request to 
the Federal Aviation Administration, Office of Rulemaking, 800 
Independence Avenue SW., Washington, DC 20591, or by calling (202) 267-
9677. Communications must identify the notice number of this NPRM.
    Persons interested in being placed on the mailing list for future 
NPRM's should request from the above office a copy of Advisory Circular 
No. 11-2A, Notice of Proposed Distribution System, which describes the 
application procedure.

History

    In 1982, the FAA announced a comprehensive plan to modernize and 
improve air traffic control and airway facilities. One part of the 
comprehensive plan included introducing the Mode S system. In an 
advance notice of proposed rulemaking, the FAA stated that improved 
surveillance reliability and accuracy would be a central objective of 
the Mode S system (48 FR 48364, October 18, 1983). Mode S transponders 
were considered an integral link in the system, furnishing accurate, 
reliable, and positive air traffic control information on aircraft 
identity, position, and altitude. The plan envisioned that all 
groundbased secondary radars would be replaced by Mode S stations, and 
that Mode S would provide the exclusive medium for an air/ground data 
link. At that time, the first 137 Mode S ground sensors were expected 
to be on-line by 1991. Therefore, the Mode S transponder requirement 
was promulgated with a final rule published February 3, 1987 (Amendment 
Nos. 121-190 and 135-22; 52 FR 3380). This final rule provided that any 
transponder newly installed in aircraft used for operations under parts 
121 and 135 of Title 14, Code of Federal Regulations (14 CFR 121 and 
135), before January 1, 1992, could be a Mode A transponder provided 
the transponder was manufactured prior to January 1, 1990; only Mode S 
transponders could be newly installed in these aircraft after January 
1, 1992.

Mode A and Mode S Transponders

    The two kinds of aircraft equipment addressed by this rulemaking 
are the Mode A and the Mode S transponders. They are the airborne 
portion of the secondary radar system, which is not a true radar system 
but rather an interrogate/respond system used to establish aircraft 
position and identity.
    The Mode A transponder consists of a radio transceiver that 
responds to a coded train of pulses from ground sensors (known as Air 
Traffic Control Radar Beacon Interrogators (ATCBI)). The Mode A 
transponder response encodes one of 4,096 discrete codes (set by the 
pilot) in response to a Mode A interrogation from the ground sensor. 
The ground sensor receives the reply message, and processors extract 
the aircraft's position and identity for display on the controller's 
radar scope. An enhanced transponder is capable of responding to Mode C 
interrogations from the ground station by reporting the aircraft's 
altitude derived from a suitable encoding altimeter.

[[Page 26037]]

    The Mode S transponder is an advanced version of the Mode A 
transponder which responds to conventional Mode A and Mode C 
interrogations, but it is also capable of responding to a Mode S 
interrogation with a unique code based on the aircraft's tail number. 
When used in conjunction with Mode S ground sensors, a system of nearly 
interference-free radar transmission and reception will exist. This 
system provides for improved target information to be display on the 
controller's radar screen and enables the various air traffic control 
computers (ATC) to detect conflict and control aircraft flow. In 
addition, the Mode S ground station recognizes a conventional Mode A 
transponder and reverts to conventional ATCBI operation for that 
aircraft.

The Mode S System

    The Mode S system was designed to rectify limitations in the 
current radar system. The limitations include synchronous garble, loss 
of target and altitude integrity, and restrictions on traffic 
management caused by the limited number of discrete beacon codes. Of 
the two components in the Mode S system (i.e., the ground sensor and 
the transponder), the ground sensor provides most of the capability to 
ameliorate these limitations.
    Synchronous garble occurs when the ground sensor interrogating two 
aircraft near one another cannot distinguish between their respective 
replies. In this situation, the data cannot be reconstructed; the ATC 
computer will either not display information or display erroneous 
information on the air traffic controller radar scope. When this 
condition can occur any time aircraft are in proximity, it is most 
likely to hamper air traffic services in areas of high density aircraft 
activity such as Classes B and C airspace areas. Improved processing 
capabilities found in the latest monopulse secondary radars are able to 
resolve many garble situations without Mode S transponder equipage by 
the aircraft. Operational experience with the currently deployed Mode S 
systems indicates that the garble resolution provided with the current 
transponder population is sufficient to provide assured separation 
using today's separation standards.
    Target and altitude integrity expresses the ability of the radar 
system to distinguish between transmissions received from two different 
aircraft. The ATCBI secondary radar system transmits interrogation 
signals, and all transponder-equipped aircraft receiving the signal 
reply with a distinct code and, if so equipped, report the aircraft's 
altitude. As described earlier, the ability of the current system to 
distinguish between two signals is affected by the proximity of the 
aircraft to each other. Terrain, signal strength of the aircraft 
transponder equipment, and environmental factors can also derogate the 
ability of the ground sensor to determine the position and altitude of 
an aircraft.
    Azimuth accuracy is improved with the Mode S system. To illustrate, 
when two aircraft are equal distances from a sensor in the existing 
system, they must be at least .23 deg. of azimuth apart before both 
targets are displayed. With the Mode S system, those same aircraft need 
only be apart by .06 deg. of azimuth to be displayed. A 1976 FAA-
sponsored study postulated that a homogeneous Mode S environment (Mode 
S ground sensors and transponders) would increase integrity to more 
than 99 percent. Recent FAA tests and operational experience with the 
Mode S ground sensors have verified these figures.
    If the number of aircraft operating in the National Airspace System 
continues to increase, the number of codes needed may eventually exceed 
the current limit of 4,096 discrete codes. Controllers assign these 
discrete codes, used to track aircraft position and altitude, to 
aircraft receiving air traffic services. The unique code assigned by 
the Mode S reduces the controller's workload and computer processing 
burden, allowing positive identification of an aircraft as it passes 
from one air traffic facility to another, and as data link messages are 
associated with surveillance targets. However, without a nationwide 
network of Mode S ground sensors in place and enhanced ATC computers 
with complementary software, these productivity benefits cannot be 
fully achieved.
    Although the Mode S system improves accuracy in the surveillance of 
aircraft position and reduces interference in identify reports 
transmitted to air traffic controllers, which allows for clear 
surveillance of aircraft that are minimally separated, studies with the 
Precision Runway Monitor show that a multitude of procedural, pilot 
training, and other issues must be addressed before a relaxation in 
aircraft separation standards may be approved. Therefore the capacity 
benefits envisioned initially from Mode S are not primarily dependent 
on improved surveillance capability.
    In addition to surveillance, the initial strategy for Mode S 
deployment includes a data-link capability. All secondary radar ground 
stations were to be converted to Mode S, which was to be the sole data 
link used for critical ATC messages. The FAA has adopted a new data 
link strategy with two principle thrusts: (1) a second FAA data link 
will be deployed as part of the next-generation air-ground VHF radios; 
and (2) private data link services will be considered if they meet FAA 
performance requirements. The message itself will be routed through an 
Aeronautical Telecommunications Network (ATN), which will automatically 
select the best air-ground media based on the nature of the message. 
This strategy provides a much more flexible and market-driven approach, 
which allows the FAA to work with the aviation community to use the 
best available evolving technology.
    The new data link strategy means that nationwide Mode S ground 
station deployment is no longer required to establish the air-ground 
link. Further, mandatory Mode S transponder equipage by aircraft is not 
required to achieve widespread data link equipage in aircraft. The 
number of Mode S ground stations will now be determined by surveillance 
requirements and the marginal benefit of the increased air-ground data 
link capability.
    Mode S capability is an integral part of the Traffic Alert and 
Collision Avoidance System II (TCAS II) required by Sec. 121.356 14 CFR 
for certain aircraft operating under part 121. This regulation requires 
such aircraft having a passenger seating configuration of more than 30 
seats to be equipped with an approved TCAS II and appropriate Mode S 
transponder by December 30, 1993. Used with TCAS II, Mode S provides 
air-to-air data exchange between TCAS-equipped aircraft making 
coordinated, complementary resolution advisories (recommended escape 
maneuvers) possible. A TCAS II system is rendered ineffective unless a 
Mode S transponder is installed with the TCAS II component.
    Traffic Alert and Collision Avoidance System I (TCAS I) does not 
require data from Mode S transponders to function. This system is 
intended for use by aircraft with passenger seating configuration 
between 10 and 30 seats that are operated under parts 121 and 135. TCAS 
I provides proximity warning only to assist a pilot in the visual 
acquisition of intruder aircraft.
    The FAA has determined that the requirement to install Mode S 
transponders after January 1, 1992, in aircraft not required to be 
equipped with TCAS II exceeds the requirements of the present and 
immediate future for a safe and efficient National Airspace System. 
Studies and analysis are being

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conducted on advanced methods of aircraft separation to support the 
FAA's goal of ``free flight.'' Free flight is an operational vision 
that will allow aircraft to cooperatively plan and execute their 
optimal flight paths with minimal interference from ground-based 
controllers. The overall infrastructure improvements to the airspace 
system (including surveillance) required to achieve operational 
benefits are being defined, and public comment will be sought on the 
benefits, procedures, and any new avionics requirements before they are 
implemented. The FAA further invites comment on whether future equipage 
of Mode S transponders should be mandatory for certain areas of 
operation.
    Except for aircraft equipped with TCAS II, the presence of Mode S 
transponder capability on part 135 aircraft would not enhance the 
safety of flight in today's airspace environment. If the demand for air 
traffic services continues to increase, A mode S transponder may be 
necessary for aircraft operating under parts 121 and 135 to increase 
efficiency in some areas of the national airspace system.

The Proposed Rule

    The FAA proposes to rescind the Mode S transponder requirement for 
aircraft operating under part 135 of the FAR and those aircraft 
operating under part 121 that are not required to have TCAS II.

Paperwork Reduction Act

    This proposed rulmaking would rescind an agency regulation and 
would not change any reporting requirements. Therefore, no review or 
approval under the Paperwork Reduction Act is required.

Regulatory Evaluation Summary

    The FAA has determined that this rulemaking is not a ``significant 
regulatory action'' as defined by Executive Order 12866 (Regulatory 
Planning and Review). The anticipated costs and benefits associated 
with this NPRM are summarized below. (A detailed discussion of costs 
and benefits is contained in the full regulatory evaluation contained 
in the docket for this NPRM.)

Overview

    Although this proposal applies to operators under parts 121 and 
135, the benefits and costs sections of this evaluation will only focus 
on part 135 operators. Of the part 121 operators, only those not 
required to install TCAS II would be affected by this proposed rule. 
The FAA is not able, at this time, to determine the number of these 
operators because there is no information readily available. For this 
reason, only the potential impact on part 135 operators will be 
analyzed in this evaluation. The FAA solicits comments from the 
aviation community as to the number of part 121 operators not required 
to have TCAS II.
    This proposed Mode S rescission would apply to all part 135 
operators regardless of what kind of transponder (remote-mounted or 
panel-mounted) they would purchase. For this evaluation, however, the 
FAA will consider only those part 135 operators who would install 
remote-mounted transponders. When the FAA estimated the benefits of the 
Mode S rescission for part 91 operators, it counted all of the panel 
mounted Mode S transponders since those transponders are predominantly 
installed in part 91 aircraft. The FAA has since learned that some 
panel-mounted transponders are also installed in part 135 aircraft, 
especially those with less than 10 seats. Thus, the FAA has not 
estimated the number of panel-mounted transponders that are being 
operated in part 135 aircraft for this proposed rule. The FAA has not 
estimated this number for two reasons. First, the proportion of new 
panel-mounted transponders that are installed in part 135 aircraft is 
very difficult to estimate. Second, even if that proportion could be 
estimated, it could not be used to calculate the benefits for the 
proposed rule since they were already used to calculate the benefits of 
rescinding the Mode S requirement for part 91 operators. Consequently, 
the benefits of the proposed rule are underestimated.

Benefits

    The benefits of this proposed rule are the cost-savings to aircraft 
operators who would be allowed to purchase Mode A transponders instead 
of Mode 2 transponders. The FAA estimates the cost-savings to be 
approximately $10 million over the next 10 years. The present value of 
these cost-savings would be $7 million (discounted, 7 percent, 1992 
dollars).
    To estimate the potential cost-savings of this proposed rule, the 
FAA estimated the number of remote-mounted transponders that would be 
installed in part 135 aircraft with 10 to 29 seats. The FAA estimates 
that 780 such aircraft are being operated in the United States. These 
aircraft make up the vast majority of aircraft that would be affected 
by the proposed rule to rescind the Mode S requirements.
    The potential benefits would be the cost-savings that these 
operators would realize when they replace an existing remote-mounted 
Mode A transponder. The proposed rule would allow them to purchase and 
install another remote-mounted Mode A transponder instead of a new 
remote-mounted Mode S transponder. To estimate these potential 
benefits, the FAA surveyed several transponder manufacturers, fixed-
based operators, and regional airlines in an effort to ascertain 
information on the frequency of Mode A transponder replacement. 
According to these industry sources, a part 135 operator would purchase 
a new transponder, on average, once every 10 years. Thus, over the next 
10 years, on average, each part 135 operator would have purchased a new 
Mode S transponder.
    Currently, an estimated 780 part 135 aircraft would potentially be 
affected by this proposed rule. Therefore, the population of part 135 
aircraft that would be affected by this proposed rule annually would be 
approximately 78 (780/10). This translates into approximately 78 
remote-mounted Mode S transponders that would be sold annually over the 
next 10 years.
    The difference in price (including installation) between the 
average remote-mounted Mode A transponder and the average remote-
mounted Mode S transponder is $12,800. This price represents the 
average cost-savings that a part 135 operator could realize as a result 
of the proposed rule to rescind Mode S requirements. Multiplying this 
cost-savings estimate of $12,800 by the number of transponders expected 
to be sold over the next 10 years would result in total potential 
benefits of $10 million (or $7 million discounted).

Costs

    The proposed rule would impose an estimated cost of $910,000 (or 
$640,000 discounted) over the next 10 years. This cost impact would 
only affect Mode S manufacturers and would be the reduction in profit 
earned from Mode S sales. (Sales from Mode S exports would not be 
affected by the NPRM.) This proposed rule would not impose costs in the 
form of either reduced aviation safety or operational efficiency. The 
expected aviation safety and operational efficiency benefits of the 
Mode S rule have not been realized because the ground sensors were 
never installed and tested. This assessment is based on the following 
analysis of each of the potential cost components.

Aviation Safety and Operational Efficiency

    Rescinding the Mode S requirement would not decrease operational 
efficiency in the air traffic control

[[Page 26039]]

system. In addition, the rescission would not decrease safety to 
aircraft operators and the flying public. While areas of high density 
air traffic may benefit from the improved target and altitude integrity 
of the Mode S system, the benefit will derive primarily from the ground 
sensor component; the limited benefit expected from the transponder 
component by itself would appear not to warrant the current Mode S 
transponder requirement for part 135 aircraft. Since those potential 
benefits have never been realized, neither aviation safety nor 
operational efficiency would decrease as a result of this proposed 
rule.

Mode S Transponder Manufacturers

    Another potential cost impact of this proposed rule would be the 
additional costs incurred by manufacturers of Mode S transponders in 
lost profits. The manufacturers of remote-mounted Mode S transponders 
have made investments in designing and developing such products. The 
potential costs to those manufactures would be: (1) The initial 
investment to develop Mode S transponders for part 135 aircraft and (2) 
the potential lost profit on each remote-mounted Mode S transponder 
sold in the future. In terms of the initial development cost, there 
would be no loss due to this proposed rule. These manufacturers have 
incurred costs for developing remote-mounted Mode S transponders in 
response to the Mode S rule. Such costs, which are in excess of $4 
million (undiscounted), are sunk and cannot be considered as part of 
the proposed rule. Once an investment is made and cannot be altered, it 
is called a sunk cost. For this reason, sunk costs are not considered 
when evaluating the costs of regulatory actions.
    In terms of profits on Mode S transponders sold in the future, the 
proposed rule would impose a cost. The proposed Mode S rescission would 
decrease the demand for remote-mounted Mode S transponders by part 135 
operators; hence, the cost to manufacturers would be lost profit. This 
lost profit would represent the difference in profit earned from sales 
of Mode A rather than Mode S transponders over the next 10 years. Due 
to the proprietary nature of such information, the FAA was unable to 
ascertain specific rates of profit that manufacturers earn on the sale 
of Mode S transponders. However, the FAA did receive information that 
indicates the profit earned on the sale of Mode A transponders is 10 
percent. The FAA contends that this rate is also a fair representation 
for Mode S transponders as well, since they are similar products 
installed in the same type of aircraft and purchased by the same part 
135 operators.
    The amount of potential lost profit (LP) is the amount of revenue 
(R) that would be earned from the sale of Mode S transponders (instead 
of Mode A transponders) less the cost (C) of manufacturing Mode S 
transponders (instead of Mode A transponders). The revenue is 
equivalent to the cost-savings incurred by aircraft operators, which is 
$7 million (discounted) over the next 10 years. The cost of 
manufacturing Mode S tranponders can be estimated based on the 
relationship between the rate of profit, the revenue and the 
manufacturing cost. In general terms, this relationship can be 
represented as R=C x P. In this instance, revenue is $7 million and 
profit is 1.10. To estimate the potential lost profit, the following 
calculation is made:

R=C x P=$7M
C=$7M/1.10=$6.36M
LP=R-C=$640,000

    As shown in the above calculation, the estimate of $640,000 
represents the present value lost profit from selling Mode A instead of 
Mode S transponders over the next 10 years. The FAA recognizes that 
there is some uncertainty in the accuracy of the rate of profit on 
transponder sales for manufacturers. This uncertainty is due, in large 
part, to the fact that the rate of profit varies among manufacturers of 
remote-mounted Mode S transponders. As the result of this uncertainty, 
the FAA solicits comments from manufacturers of remote-mounted Mode S 
transponders as to the accuracy of the 10 percent rate of profit 
estimate.

Conclusion

    The potential cost-relieving benefits of this proposed rule are 
estimated to be $7 million (discounted). The potential costs are 
estimated to be $640,000 (discounted). Based on this assessment, the 
FAA has determined that this proposed rule is cost-beneficial.

Initial Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily burdened 
by government regulations. The RFA requires agencies to review rules 
that may have a ``significant economic impact on a substantial number 
of small entities.''
    According to the FAA's Regulatory Flexibility Criteria and Guidance 
(2100.14A), a substantial number of small entities means a number that 
is not less than 11 and that is more than one third of the small 
entities subject to the proposed rule. The small entities that this 
proposed rule would potentially affect are aircraft flight instrument 
manufacturers that produce no more than 250 units annually. The FAA has 
identified the three manufacturers that produce remote mounted Mode S 
transponders. On average, these three manufacturers combined sell 
approximately 2,200 transponders annually. Each of the three 
manufacturers sell, on average, approximately 730 (2,200/3) Mode S 
transponders annually. Since 730 exceeds the annual size threshold of 
250, none of the U.S. Mode S transponder manufacturers are considered 
to be small. Thus, this proposed rule would not impose a significant 
economic impact on a substantial number of small entities. For this 
reason, a regulatory flexibility analysis is not required.

International Trade Impact Assessment

    The Office of Management and Budget directs agencies to assess the 
effects of regulatory changes on international trade. This proposed 
rule would not have a competitive trade disadvantage on foreign 
companies that sell foreign aviation products or services in the United 
States. This proposed rule also would not have a competitive trade 
disadvantage on domestic companies that sell U.S. products or services 
in foreign countries. This assessment is based on the belief that the 
number and type of transponders sold to foreign operators by U.S. 
manufacturers would not change as a result of this proposed rescission. 
The FAA was not able to identify any foreign manufacturers that sell 
transponders in the United States. Based on this information, the FAA 
contends that there would be no impact on them. However, the FAA 
solicits any comments on the international trade impact.

Federalism Implications

    The proposed rescission of the regulation herein would 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 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.

Conclusion

    For the reasons discussed in this preamble and based on the 
findings in

[[Page 26040]]

the Regulatory Flexibility Determination and the International Trade 
Impact Analysis, the FAA has determined that the proposed rescission of 
this regulation is not significant under Executive Order 12866. In 
addition,the FAA certifies that this rule will not have a significant 
economic impact on a substantial number of small entities under the 
criteria of the Regulatory Flexibility Act. This proposal is considered 
not significant under DOT Regulatory Policies and Procedures (44 FR 
111034; February 26, 1979). A regulatory evaluation of the regulation, 
including a Regulatory Flexibility Determination, and International 
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

14 CFR Part 121

    Air carriers, Aircraft, Aviation safety, Charter flights, 
Transportation.

14 CFR Part 135

    Air taxis, Aircraft, Aviation safety.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend parts 121 and 135 of Title 14, Code of 
Federal Regulations (14 CFR parts 121 and 135) as follows:

PART 121--CERTIFICATION AND OPERATIONS: DOMESTIC, FLAG, AND 
SUPPLEMENTAL AIR CARRIERS AND COMMERCIAL OPERATORS OF LARGE 
AIRCRAFT

    1. The authority citation for part 121 continues to read as 
follows:

    Authority: 49 U.S.C. 106(g), 40113, 40119, 44101, 44701-44702, 
44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-44904, 
44912, 46105.

    2. Section 121.345(c) is revised to read as follows:


Sec. 121.345  Radio equipment.

* * * * *
    (c) ATC transponder equipment installed after January 1, 1992, must 
meet the performance and environmental requirements of the following 
TSO's:
    (1) For aircraft not required to be equipped with an approved TCAS 
II traffic alert and collision avoidance system pursuant to 
Sec. 121.356, any class of TSO-C74b or TSO-C74c, as appropriate, or the 
appropriate class of TSO-C112 (Mode S).
    (2) For aircraft required to be equipped with an approved TCAS II 
traffic alert and collision avoidance system pursuant to Sec. 121.356, 
the appropriate class of TSO-C112 (Mode S).

PART 135--AIR TAXI OPERATORS AND COMMERCIAL OPERATIONS

    1. The authority citation for part 135 continues to read as 
follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44709, 
44711-44713, 44715-44717, 44722.

    2. Section 135.143(c) is revised to read as follows:


Sec. 135.143  General requirements.

* * * * *
    (c) ATC transponder equipment installed after January 1, 1992, must 
meet the performance and environmental requirements of any class of 
TSO-C74b or TSO-C74c, as appropriate, or the appropriate class of TSO-
C112 (Mode S).

    Issued in Washington, DC on May 15, 1996.
William J. White,
Acting Director, Flight Standards Service.
[FR Doc. 96-13030 Filed 5-22-96; 8:45 am]
BILLING CODE 4910-13-M