Notification to Air Traffic Control (ATC) of Deviations From ATC Clearances in Response to Traffic Alert and Collision Avoidance System Resolution Advisories

SUMMARY: This action codifies the previously announced policy extended

to pilots during the initial testing of the Traffic Alert and Collision

Avoidance System (TCAS) during the Limited Implementation Plan for

TCAS, and during the actual implementation of TCAS under the TCAS

Transition Plan (TTP). This policy permitted pilots to deviate from an

air traffic control (ATC) clearance, in non-emergency situations, when

responding to a TCAS resolution advisory (RA). The language contained

in current regulations suggests that deviation from an ATC clearance is

authorized only in an emergency situation. The intended effect of this

action is to add the TCAS RA as a reason to deviate from a clearance,

and to require that whenever a pilot deviates from an ATC clearance,

ATC will be advised as soon as possible.

EFFECTIVE DATE: October 30, 1995.

FOR FURTHER INFORMATION CONTACT:

Mrs. Ellen Crum, Air Traffic Rules Branch, ATP-230, Airspace Rules and

Aeronautical Information Division, Federal Aviation Administration, 800

Independence Avenue, SW., Washington, DC 20591; telephone (202) 267-

8783.

SUPPLEMENTARY INFORMATION:

Background

On December 26, 1989, the FAA published a petition for rulemaking,

received from the Air Transport Association of America (ATA), that

requested the FAA amend section 91.75(a) of the Federal Aviation

Regulations (FAR) to permit a pilot to deviate from an ATC clearance

when responding to a TCAS RA (54 FR 52951). (Effective August 18, 1990,

part 91 of the FAR was revised (54 FR 34284; August 18, 1989) to

renumber all of its sections. Section 91.75(a) was renumbered as

section 91.123(a).)

Section 91.123 of the FAR states, in pertinent part, that each

pilot in command who, in an emergency, deviates from an ATC clearance

shall notify ATC of that deviation as soon as possible. The ATA

petition states that TCAS is an advisory system and not an emergency

system. The ATA feels that pilots should be able to comply with a TCAS

RA without exercising emergency authority. The ATA petition mirrors

current FAA policy and guidance for the use of TCAS II. The petition

drew no negative comments and one positive comment from the Airline

Pilots Association (ALPA) that supported the proposal.

On April 9, 1994, the FAA published a Notice of Proposed Rulemaking

(59 FR 22142, Notice No. 94-16) that proposed to amend Section

91.123(a) of the FAR in accordance with the ATA petition. In addition,

this NPRM proposed to amend Sec. 91.123(c) of the FAR to require pilots

to notify ATC as soon as possible if they deviate from a clearance in

response to a RA. The comment period for this NPRM closed on May 31,

1994 and comments are discussed later in this document.

Currently, regulations do not provide for any deviation from an ATC

clearance except in an emergency situation. However, during the initial

trial and implementation of TCAS II, the FAA notified pilots that no

enforcement action would be initiated if the pilot deviated from an ATC

clearance when responding to a TCAS RA. A letter signed by former FAA

Administrator James B. Busey was published as Appendix C to the TTP

Project Management Plan, dated August 1, 1990. The FAA also provided

procedural guidance in Advisory Circular 120-55, ``Air Carrier

Operational Approval and Use of TCAS II'' dated October 23, 1991, and

later amended as AC 120-55A dated August 27, 1993. The policy and

guidance proved successful during the testing and implementation of

TCAS II.

Related Agency Actions

On January 10, 1989, the FAA published a final rule (54 FR 940),

known as the ``TCAS rule,'' that required airplanes having more than 30

passenger seats and operated under part 121, 125, or 129 to be equipped

with TCAS II by December 30, 1991. The TCAS rule also required

airplanes having 10 to 30 passenger seats and operated under part 129

or 135 to be equipped with TCAS I by February 9, 1995; this compliance

date was subsequently extended to December 31, 1995 (59 FR 67584,

December 29, 1994). On April 9, 1990, the FAA amended the TCAS rule by

revising the schedule for the installation of TCAS II equipment in

airplanes having more than 30 passenger seats (55 FR 13242). Operators

of airplanes having more than 30 passenger seats and operated under

part 121 were required to install TCAS II equipment in accordance with

a phased-in schedule so that 100% of an operator's covered airplanes

would be equipped by December 30, 1993. Operations conducted under part

125 or 129 with airplanes having more than 30 passenger seats were also

required to install TCAS II equipment by December 30, 1993.

TCAS

TCAS is airborne equipment that interrogates ATC transponders of

other aircraft nearby. By computer analysis of the replies, TCAS

equipment determines which transponder-equipped aircraft are potential

collision hazards and provides appropriate advisory information to the

flight crew. If a TCAS-equipped airplane interrogates an aircraft that

is equipped with a transponder without altitude reporting capability

(Mode A), range and azimuth information will be provided to the TCAS-

equipped aircraft. If the interrogated aircraft is equipped with an

altitude encoding transponder (Mode C or Mode S), then relative

altitude information will be provided in addition to range and azimuth.

TCAS equipment cannot detect the presence of an aircraft that is not

equipped with a transponder.

TCAS equipment performs proximity tests on each detected target. If

the path of a target is projected to pass within certain horizontal and

vertical distance criteria, then that target is declared an intruder.

An intruder that is determined to pose an even greater risk of

collision is declared a threat. When a threat is declared, TCAS

equipment will determine the appropriate direction that the TCAS-

equipped aircraft must move (climb or descend) and the vertical rate

that must be maintained to achieve separation from the threat.

There are two classes of advisories provided by TCAS equipment. The

first class, the ``traffic advisory'' (TA), provides supplemental

information to the pilot that aids in visual detection of other

aircraft. TA's include the range, bearing, and if the intruder has

altitude-reporting equipment, the altitude of intruding aircraft

relative to the TCAS equipped aircraft. TA's without altitude

information may also be provided from non-altitude reporting

transponder-equipped intruders. TCAS I equipment provides TA's that

only assist the pilot in visually detecting an intruder aircraft. The

second class of advisory, the ``resolution advisory'' (RA), indicates

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the vertical direction and rate that must be achieved by an aircraft in

order to prevent insufficient separation. When an RA occurs, the pilot

flying should respond by direct attention to RA displays and should

maneuver as indicated unless doing so would jeopardize the safe

operation of the flight or unless the flight crew has definitive visual

acquisition of the aircraft causing the RA. TCAS II equipment provides

both traffic and resolution advisories only in the vertical plane.

The Rule

This rule accomplishes two things. First, it authorizes deviations

from an ATC clearance when responding to a TCAS RA. Secondly, it

requires pilots to notify ATC as soon as possible if they deviate from

a clearance in response to a TCAS RA. This action codifies existing

policies and practices that were initiated during the TCAS

implementation period.

Discussion of Comments

Interested persons were invited to participate in this rulemaking

action by submitting written data, views, or arguments. All comments

received during the comment period were considered before making a

determination regarding this final rule. The following is a discussion

of the comments received.

Five comments were received in response to the NPRM. Of this

number, three comments were received from associations and two from

individuals. Most commenters supported amending FAR 91.123(a); however,

three commenters opposed amending FAR 91.123(c).

I. Compliance With ATC Clearances

Most commenters support this amendment which allows flight crews to

deviate from an air traffic control clearance in response to a TCAS RA.

The Air Transport Association of America (ATA) and the Air Line Pilots

Association (ALPA) stated that the proposal is fully consistent with

the ATA petition referenced in the Notice. ATA believes this action

will remove a potential obstacle to the full use of TCAS by allowing

flight crews to follow a TCAS RA without pausing to determine if the RA

maneuver would require the crew to declare an emergency. Another

commenter states that he believes safety would be improved with this

amendment, and supports it. The National Air Traffic Controllers

Association (NATCA) did not comment specifically on this proposed

change, but offers general comments stating they do not believe the air

traffic system is as safe today as it was prior to the introduction of

TCAS.

On December 30, 1987, the President of the United States signed

Public Law 100-223 which, among other provisions, amended the FAA Act

of 1958, Section 601, by adding a new paragraph (f) entitled

``Collision Avoidance Systems.'' This section requires TCAS II on

``each civil aircraft of more than 30 seats and which is used to

provide air transportation of passengers, including intrastate air

transportation of passengers.'' The amendment does not provide for the

exception of any class of civil operation or operator, U.S. or foreign,

from the basic rule. Consequently, the FAA promulgated numerous

regulations (several of which have been referenced earlier in this

document) pertaining to TCAS. In addition, the TTP, along with the

Separation Assurance Task Force (SATF), were established to investigate

and resolve TCAS related problems in the NAS which are discovered

during implementation. Participants in this program include the FAA,

ATA, Regional Airline Association, ALPA, Allied Pilots Association,

NATCA, Transport Canada, TCAS equipment manufacturers and the major,

national and regional air carriers.

The FAA disagrees with NATCA's view that TCAS has compromised

safety. Since the introduction of TCAS into the NAS, both air traffic

controllers and flight crews have adjusted their operating procedures.

With the assistance and cooperation of flight crews and air traffic

controllers, surveys have been collected and volumes of data analyzed.

As issues surface, the TTP provides guidance for timely resolution that

has resulted in better training for both pilots and controllers, the

issuance of two advisory circulars addressing the use of TCAS,

amendments to the controllers handbook and the Airman's Information

Manual (AIM), and updating the TCAS software in order to eliminate

false and nuisance RA's.

At the second annual International TCAS Conference held in Reston,

Virginia in September, 1993, TCAS was lauded by many flight crews as a

safety enhancing cockpit device.

For example, TCAS was credited by the captain of a major air

carrier for saving the lives of nearly 700 people in two B747 aircraft

traveling over the Pacific Ocean.

The TCAS Industry Alert Bulletin #5, issued February 18, 1994,

states that during the prior two years, 16 encounters had occurred

wherein TCAS II displayed unnecessary resolution advisories that

directed pilots to cross through each other's altitudes. The RA's were

unnecessary because the aircraft were safely separated by the ATC

system. In each of these encounters, the TCAS logic detected the high

vertical closure rate of the two aircraft and predicted the close

proximity of the aircraft without knowing that the aircraft intended to

level off 1000 feet apart in altitude.

In order to eliminate these unnecessary RA's, a new version of the

TCAS logic (Version 6.04A) was created and installation required by 12/

31/94. This logic will not generate altitude-crossing RAs when aircraft

level off within 1000 feet vertically of one another. None of the 16

encounters previously mentioned would have resulted in altitude-

crossing RAs with the Version 6.04A logic installed.

II. ATC Notification

ATA and ALPA oppose this proposal which requires flight crews to

inform ATC as soon as possible when deviating from an ATC clearance in

response to a TCAS RA. ALPA states they do not oppose notifying ATC of

any deviation caused by responding to a TCAS RA; however, they believe

the proposal may imply a sense of urgency for pilots to advise ATC of a

deviation at a time when complete attention must be focused on

identifying the intruder and responding to the RA. ALPA states this

sense of urgency may also be prompted by a concern over possible

enforcement action should the crew neglect to report the event due to a

directed frequency change or some other unanticipated event. ATA

comments that the phrase ``as soon as possible'' implies that

notification to ATC of a deviation should take place prior to executing

the maneuver. ATA suggests the word ``practical'' be used in lieu of

``possible'' which would be consistent with the AIM.

The FAA does not agree with replacing the word ``possible'' with

``practical''. The word ``possible'' does not mean that the

notification has to take place before the pilot has executed the

appropriate maneuver. ``Possible'' does, however, contain a greater

urgency than the word ``practical,'' and would require notification to

ATC of the deviation as soon as the pilot maneuvers the aircraft to a

safe operating environment. The language is consistent with current

wording contained in the regulation that requires a flight crew who, in

an emergency, deviates from an ATC clearance to notify ATC as soon as

possible. If a pilot deviates from an ATC clearance, the controller

must be given timely notification of that deviation so that appropriate

instructions and/or

[[Page 50678]]

advisories can be issued to ensure a safe, orderly, and expeditious

flow of traffic. By advising ATC as soon as possible that an RA has

been received, the controller can evaluate the situation, determine the

most appropriate and safe course of action, and issue alternate

instructions if necessary.

ALPA states that the requirement to report a deviation from an ATC

clearance as a result of an RA is stated in the Airman's Information

Manual (AIM), FAA Advisory Circular 120-55, and each TCAS equipped

aircraft flight operations manual. Consequently, the commenter believes

this proposal is redundant and unnecessary.

The FAA acknowledges there are several FAA publications which

explain and encourage pilots to communicate with ATC when deviating

from a clearance upon receipt of a RA. However, the FAA has determined

that safety within the NAS can only be maintained if pilots are

required to advise controllers when a deviation from an ATC clearance

has occurred as a result of an RA.

NATCA opposes this rule change due to concerns for the safety of

persons operating in the NAS. However, NATCA does not provide specific

instances of how or where safety is compromised, but merely reiterates

their ongoing concern with the TCAS program.

The FAA has determined that pilot notification of a deviation from

a clearance due to a TCAS RA enhances safety in the NAS. Air traffic

controllers base their control and traffic management decisions on the

expectation that pilots will comply with ATC-assigned routes,

altitudes, and other clearances. If a pilot deviates from an ATC

clearance, the controller must be given timely notification of that

deviation so that appropriate instructions and/or advisories can be

issued to ensure a safe, orderly, and expeditious flow of traffic. By

advising ATC as soon as possible that an RA has been received, the

controller can evaluate the situation, determine the most appropriate

and safe course of action, and issue alternate instructions if

necessary.

III. Resolution Advisory Maneuver--An Emergency?

One commenter contends that any deviation from an ATC clearance is

an emergency; therefore, this rule change is not needed. The commenter

believes the cause of the deviation need not be an emergency, but the

mere fact that an aircraft is not following an ATC clearance should be

considered an emergency. The commenter suggested the phrase ``in an

emergency'' be deleted from the rule; thereby, any time an aircraft

deviates from an ATC clearance, regardless of the reason, ATC will be

notified.

The FAA disagrees that an RA maneuver is an emergency action. TCAS

is designed to serve as a backup (safety net) to visual collision

avoidance, application of ``right of way rules'', and air traffic

separation services. Since its inception, TCAS has been considered by

the FAA and industry to be a supplement to the ATC system that provides

flight guidance to ensure adequate separation from other aircraft.

Additionally, although the suggestion to remove the word ``emergency''

from the language of the regulations is outside the scope of this

rulemaking, the FAA will consider the merits of the comment for

possible future rulemaking.

Regulatory Evaluation Summary

Executive Order 12866 established the requirement that, within the

extent permitted by law, a Federal regulatory action may be undertaken

only if the potential benefits to society for the regulation outweigh

the potential costs to society. In response to this requirement, and in

accordance with Department of Transportation policies and procedures,

the FAA has estimated the anticipated benefits and costs of this

rulemaking action. The results are stated in this section. The FAA has

determined that this rule change is not a ``significant rulemaking

action,'' as defined by Executive Order 12866 (Regulatory Planning and

Review).

The FAA has determined that this rule will be cost-beneficial

because it imposes no costs and would promote air safety. There will

not be any changes in notification or reporting requirements for

deviations from ATC clearances that are necessary to avoid potential

collision hazards. This action codifies a previously announced policy

that pilots who deviate from their assigned altitudes in response to a

TCAS RA will provide timely notice, as soon as possible, to air traffic

control. Such non-written, voice notification will give controllers an

opportunity to resolve any conflicts resulting from a TCAS II-equipped

aircraft being at other than the assigned altitude.

International Trade Impact Statement

This action will not impose a competitive disadvantage to either

U.S. air carriers doing business abroad or foreign air carriers doing

business in the United States. This assessment is based on the fact

that this rule will not impose additional costs on either U.S. or

foreign air carriers.

Regulatory Flexibility Determination

In accordance with the Regulatory Flexibility Act of 1980, the FAA

has determined that this action will not have a significant economic

impact, positive or negative, on a substantial number of small

entities. This assessment is based on the fact action will not impose

any additional cost on aircraft operators.

Paperwork Reduction Act

There are no requirements for information collection associated

with this action that would require approval from the Office of

Management and Budget pursuant to the Paperwork Reduction Act of 1980

(Pub. L. 96-511).

Federalism Implications

This regulation 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 does not have sufficient

federalism implications to warrant the preparation of a Federalism

Assessment.

International Civil Aviation Organization and Joint Aviation

Regulations

In keeping with the U.S. obligations under the Convention on

International Civil Aviation (ICAO), it is FAA policy to comply with

ICAO Standards and Recommended Practices (SARP) to the maximum extent

practicable. The FAA has determined that this action complies with the

ICAO SARP.

Conclusion

For the reasons discussed in the preamble, and based on the

findings in the Regulatory Flexibility Determination and the

International Trade Impact Analysis, the FAA has determined that this

regulation is not a ``significant regulatory action'' under Executive

Order 12866. This regulation is not considered significant under DOT

Order 2100.5, Policies and Procedures (44 FR 11034; February 26, 1979).

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.

List of Subjects in 14 CFR Part 91

Air traffic control, Aircraft, Aviation safety.

[[Page 50679]]

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:

PART 91--GENERAL OPERATING AND FLIGHT RULES

1. The authority citation for part 91 continues to read as follows:

Authority: 42 U.S.C. 4321 et seq.; 49 U.S.C. app. 1301, 1303,

1344, 1348, 1352 through 1355, 1401, 1421 through 1431, 1471, 1472,

1502, 1510, 1522, and 2121 through 2125, 2157, 2158; 49 U.S.C.

106(g); articles 12, 29, 31, and 32(a) of the Convention on

International Civil Aviation (61 Stat. 1180); E.O. 11514, 35 FR

4247, 3 CFR, 1966-1970 Comp., p. 902.

2. Section 91.123 is amended by revising paragraphs (a) and (c) to

read as follows:

Sec. 91.123 Compliance with ATC clearances and instructions.

(a) When an ATC clearance has been obtained, no pilot in command

may deviate from that clearance unless an amended clearance is

obtained, an emergency exists, or the deviation is in response to a

traffic alert and collision avoidance system resolution advisory.

However, except in Class A airspace, a pilot may cancel an IFR flight

plan if the operation is being conducted in VFR weather conditions.

When a pilot is uncertain of an ATC clearance, that pilot shall

immediately request clarification from ATC.

* * * * *

(c) Each pilot in command who, in an emergency, or in response to a

traffic alert and collision avoidance system resolution advisory,

deviates from an ATC clearance or instruction shall notify ATC of that

deviation as soon as possible.

* * * * *

Issued in Washington, D.C. on September 13, 1995.

David R. Hinson,

Administrator.

[FR Doc. 95-24170 Filed 9-28-95; 8:45 am]

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