Airworthiness Directives: Terra Corporation TRT 250 Series Transponder

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-SW-03-AD]

Airworthiness Directives: Terra Corporation TRT 250 Series

Transponder

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to the Terra Corporation TRT 250

series transponder (transponder). This proposal would require removing

the transponder from the aircraft, inspecting it to determine if the AD

applies, and replacing any affected transponder with a modified Terra

Corporation transponder or another transponder that responds properly

to Mode S interrogations from both an ATCRBS/Mode S ground station and

TCAS II airborne equipment. This proposal is prompted by FAA tests that

show that the transponder does not reply to certain interrogations by a

Mode S or Traffic Collision Avoidance System (TCAS) II signal. The

actions specified by the proposed AD are intended to prevent failure of

the transponder to reply to Mode S interrogations from both Mode S

ground stations and TCAS II airborne equipment which could result in

loss of airspace separation.

DATES: Comments must be received by June 27, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Office of the Assistant Chief Counsel, Attention:

Rules Docket No. 94-SW-03-AD, 2601 Meacham Boulevard, room 663, Fort

Worth, Texas 76137-4298. Comments may be inspected at this location

between 9 a.m. and 3 p.m., Monday through Friday, except Federal

holidays.

The service information referenced in the proposed rule may be

obtained from Terra Corporation, 3520 Pan American Freeway NE,

Albuquerque, New Mexico 87107-4796. This information may be examined at

the FAA, Office of the Assistant Chief Counsel, 2601 Meacham Boulevard,

room 663, Fort Worth, Texas.

FOR FURTHER INFORMATION CONTACT:

Mr. George R. Hash, Aerospace Engineer, Airplane Certification Office,

FAA, Rotorcraft Directorate, 2601 Meacham Boulevard, Fort Worth, Texas

76137, telephone (817) 222-5134, fax (817) 222-5959.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule by submitting such written data, views, or arguments as

they may desire. Communications should identify the Rules Docket number

and be submitted in triplicate to the address specified above. All

communications received on or before the closing date for comments,

specified above, will be considered before taking action on the

proposed rule. The proposals contained is this notice may be changed in

light of the comments received.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the proposed rule. All

comments submitted will be available, both before and after the closing

date for comments, in the Rules Docket for examination by interested

persons. A report summarizing each FAA-public contact concerned with

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed

stamped postcard on which the following statement is made: ``Comments

to Docket Number 94-SW-03-AD.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request

to the FAA, Office of the Assistant Chief Counsel, Attention: Rules

Docket No. 94-SW-03-AD, 2601 Meacham Boulevard, room 663, Fort Worth,

Texas 76137-4298.

Discussion

This notice proposes the adoption of a new airworthiness directive

(AD), that is applicable to the Terra Corporation TRT 250 transponder,

part number (P/N) 0900-0250-00, with serial numbers (S/N) 4194 and

below, Modification Level (Mod Level) 4 and below; 3-inch ATI-mounted

TRT 250 push-button transponders, P/N 0900-0250-20, with S/N 5324 and

below, Mod Level 4 and below; and, TRT 250 D digital display

transponders, P/N 0900-0250-30, with S/N 1155 and below, Mod Level 1

and below (transponder). Recent FAA tests have shown that these

transponders do not reply to Air Traffic Control Radio Beacon System

(ATCRBS) only or ATCRBS/Mode S ``all-call'' interrogations by a Mode S

ground sensor. The affected transponder processes interrogation data

beyond the P3 pulse as an invalid interrogation, which causes it

to suppress the reply. The Mode S ground stations and the TCAS II

airborne equipment interrogates beyond the P3 pulse. This

inability of the affected transponder to reply to valid interrogations

creates an unsafe condition. This condition, if not corrected, could

result in failure of the transponder to reply to Mode S interrogations

from Mode S ground stations and TCAS II airborne equipment, which could

result in loss of airspace separation.

The FAA has reviewed and approved Terra Corporation Mandatory

Service Bulletin SB-104, dated March 14, 1994, that describes

procedures for modifying the transponder and then performing a final

test procedure on the transponder unit.

Since an unsafe condition has been identified that is likely to

exist or develop on other products of this same type design, the

proposed AD would require, within 6 months after the effective date of

this AD, removal of the transponders to determine the P/N, S/N, and Mod

Level. This proposal would also require replacement of any affected

transponder with an appropriately modified Terra Corporation

transponder or another transponder that responds properly to Mode S

interrogations from both an ATCRBS/Mode S ground station and TCAS II

airborne equipment.

The FAA has temporarily altered the Mode S ground sensors to permit

the affected transponder to function normally. However, in order to

make the Mode S ground sensors operational in support of the new

national digital communication data link implementation, this temporary

alteration will be removed following the replacement of all the

affected transponders. The AD proposes to allow 6 months for

replacement of the affected transponders.

The FAA estimates that 5,000 aircraft of U.S. registry would be

affected by this proposed AD, that it would take approximately 1.5 work

hours to accomplish the proposed actions, and that the average labor

rate is $55 per work hour. Required parts would cost approximately $298

per transponder. Based on these figures, the total cost impact of the

proposal on U.S. operators is estimated to be $1,902,500.

The regulations proposed 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.

For the reasons discussed above, I certify that this proposed

regulation (1) is not a ``significant regulatory action'' under

Executive Order 12866; (2) is not a ``significant rule'' under the DOT

Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);

and (3) if promulgated, 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. A copy of the draft

regulatory evaluation prepared for this action is contained in the

Rules Docket. A copy of it may be obtained by contacting the Rules

Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend

part 39 of the Federal Aviation Regulations (14 CFR part 39) as

follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

Terra Corporation: Docket No. 94-SW-03-AD.

Applicability: Model TRT 250 transponders, part number (P/N)

0900-0250-00, with serial numbers (S/N) 4194 and below, Modification

Level (Mod Leval) 4 and below; 3-inch ATI-mounted TRT 250 push-

button transponders, P/N 0900-0250-20, with S/N 5324 and below, Mod

Levels 4 and below; and, TRT 250 D digital display transponders, P/N

0900-0250-30, with S/N 1155 and below, Mod Level 1 and below

(transponder).

Compliance: Required as indicated, unless accomplished

previously.

To prevent failure of the transponder to respond properly to

Mode S interrogations from Mode S ground stations and Traffic

Collision Avoidance System (TCAS) II airborne equipment, which could

result in loss of airspace separation, accomplish the following:

(a) Within 6 months after the effective date of this AD, remove

the TRT 250 series transponder in accordance with the procedures

stated in the Accomplishment Section of Terra Corporation Mandatory

Service Bulletin No. SB-104 (SB-104), dated March 14, 1994, and

determine the part number (P/N), serial number (S/N), and

modification level (Mod Level).

(b) If the determination made in paragraph (a) reveals one of

the affected part numbers, serial numbers, and modification levels

indicated in this AD, replace the affected transponder with:

(1) A Terra Corporation transponder that has modified in

accordance with the provisions of SB-104, dated March 14, 1994;

(2) An unaffected Terra Corporation transponder; or,

(3) Another manufacturer's transponder that responds properly to

Mode S interrogations from both an ATCRBS/Mode S ground station and

TCAS II airborne equipment.

(c) If installing a replacement Terra Corporation transponder

that has been modified in accordance with the provisions of SB-104,

dated March 14, 1994, perform a ramp test in accordance with the

Testing section of SB-104, dated March 14, 1994. Conduct the tests

and checks required by Sec. 91.413 of the Federal Aviation

Regulations (14 CFR 91.413) prior to approving the aircraft for

return to service.

(d) Installation of an affected Terra Corporation transponder

modified and tested in accordance with SB-104, dated March 14, 1994,

or another transponder that responds properly to Mode S

interrogations from both an ATCRBS/Mode S ground station and TCAS II

airborne equipment constitutes terminating action for the

requirements of this AD.

(e) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used when approved by the Manager, Airplane Certification Office,

FAA, Rotorcraft Directorate. Operators shall submit their requests

through an FAA Principal Maintenance Inspector, who may concur or

comment and then send it to the Manager, Airplane Certification

Office.

Note: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Airplance Certification Office.

Issued in Fort Worth, Texas, on May 18, 1994.

Eric Bries,

Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 94-12868 Filed 5-25-94; 8:45 am]

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