Airworthiness Directives; Terra Corporation TRT 250 Series Transponders

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 94-SW-03-AD; Amendment 39-9112; AD 95-01-01]

Airworthiness Directives; Terra Corporation TRT 250 Series

Transponders

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD),

applicable to Terra Corporation TRT 250 series transponders, that

requires 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 Air

Traffic Control Radio Beacon System (ATCRBS)/Mode S ground station and

Traffic Collision Avoidance System (TCAS) II airborne equipment. This

amendment is prompted by FAA tests that show that the transponder does

not respond properly to certain interrogations by a Mode S or TCAS II

signal. The actions specified by this AD are intended to prevent

failure of the transponder to respond properly to Mode S interrogations

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

could result in loss of airspace separation.

DATES: Effective February 6, 1995.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of February 6, 1995.

ADDRESSES: The service information referenced in this AD 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 Blvd.,

Room 663, Fort Worth, Texas; or at the Office of the Federal Register,

800 North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Mr. George R. Hash, Aerospace

Engineer, Airplane Certification Office, FAA, Rotorcraft Directorate,

2601 Meacham Blvd., Fort Worth, Texas 76137, telephone (817) 222-5134,

fax (817) 222-5959.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

Aviation Regulations (14 CFR part 39) to include an airworthiness

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

transponders was published in the Federal Register on May 26, 1994 (59

FR 27249). The original comment period was open for 30 days. However,

subsequently, the FAA determined that the original comment period was

inadequate and reopened the comment period on September 6, 1994 (59 FR

46007) with no additional changes in the proposed rule. That action

proposed to 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.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Thirty-four comments were received

from thirty-one commenters. Three of the commenters responded twice and

two commenters commented on two different items contained in the Notice

of Proposed Rulemaking (NPRM). Due consideration has been given to the

comments received. Two commenters request that certain information be

included in the preamble language that further explains the history

behind these transponders and this AD. These commenters request that

language be inserted in the final rule stating that: (1) these

transponders have been produced since 1985; (2) these transponders meet

the requirements of Technical Service Order (TSO)-C74c; (3) the Mode S

ground stations and the TCAS II airborne equipment interrogates beyond

the ATCRBS interrogation for which these transponders were designed

instead of stating that the Mode S and TCAS II interrogates beyond the

P3 pulse; and (4) the economic analysis that shows the $298 as the

cost of the required parts not only includes the cost of the parts, but

also the labor required to modify the affected transponders. While the

FAA agrees with the substance of these comments, they are not proposing

any changes to the AD language; therefore, no changes are made to the

AD based upon these comments.

Four commenters state that this AD should be published as an

immediately adopted final rule because of its serious safety

implications. The FAA does not concur. The FAA determined that, based

upon the impact of the proposed requirements of this AD, it was

appropriate to acquire as many public comments as possible prior to

finalizing the actions. Therefore, the FAA published an NPRM soliciting

public comments. To ensure the safety of flight, the Mode S ground

stations are temporarily altered to permit the affected transponders to

respond properly to ATCRBS interrogations during the compliance period.

Another two commenters state that there is no justification for an

extended compliance period and that compliance should be required as

soon as possible. The FAA does not concur that a compliance time of

less than 6 months is appropriate. With an estimated 5,000 transponders

in the field that require replacement or modification, a compliance

time of less than 6 months would not allow adequate time for all

transponders to be modified or replaced.

Two commenters state that longer compliance times should be

provided within which to modify these transponders because no

significant safety hazard exists. The FAA does not concur. In April

1994, Terra Corporation notified its customers of the forthcoming FAA

AD against the TRT 250 series transponders. The FAA informed the public

via the NPRM process in May 1994, and provided a 30-day comment period.

The comment period for the NPRM was reopened in September 1994 to

provide another 60 days for additional comments. Public notices

appeared in several aviation trade publications during this period. The

manufacturer indicates that several hundred transponders have been

modified since the May 1994 publication of the NPRM. Transport aircraft

that utilize TCAS II and Mode S transponders cannot detect those

aircraft equipped with a Terra transponder built according to the

requirements of TSO-C74c. As a direct result of the Terra transponder

problem, a thorough evaluation and a complete implementation of Mode S

ground sensors cannot occur until the transponders are modified. In

summary, this AD establishes the existence of an aviation safety

problem, and the FAA has allowed an appropriate compliance time for

action by owners or operators.

One commenter states that the FAA employee or employees involved

with the approval of the original transponder's design should pay for

the costs of modifying the transponders. The FAA does not concur. The

FAA as an agency is responsible for all directives, policies, mandates,

etc., issued under its authority, and does not penalize employees for

actions committed in good faith and within the scope of their duties.

Twenty-two commenters state that since the FAA is responsible for

the transponder's design problems, either because of the FAA's short-

sighted approval of the TSO used to produce these transponders, or

because it decided to implement the Mode S ground sensors without

adequate research and testing to determine whether all transponders

would respond properly to the interrogations, the FAA should bear the

costs associated with modifying these transponders. The FAA does not

concur with the commenters. Although the FAA has determined that a

safety problem exists with the transponder's design, the manufacturer

is responsible for the design. The technical performance standards for

airborne air traffic control (ATC) transponder equipment (TSO-C74c)

were developed by a committee comprised of both government and industry

representatives. A representative of the transponder manufacturer is

included on the membership list for that committee. There have been no

reports of other manufacturers having a similar transponder design

deficiency. Additionally, the FAA's budget does not include allocations

to cover AD costs incurred in modifying privately-owned equipment.

Since the issuance of the NPRM, the manufacturer has issued

Revision 1 to Mandatory Service Bulletin (MSB) No. SB-104 on June 27,

1994. This revision adds an additional optional modification method to

the original MSB No. SB-104, dated March 14, 1994, that was proposed to

be incorporated by reference in the NPRM. Since the revised MSB imposes

no additional burden on operators and is an optional relieving

provision, MSB No. SB-104, Revision 1, dated June 27, 1994, is

incorporated by reference in this final rule. Additionally, since the

issuance of the NPRM, the FAA has reevaluated the labor rate, and based

upon this evaluation, has increased the hourly labor rate to $60 per

work hour instead of the proposed $55 per work hour. This change

increases the estimated overall cost of this AD by $37,500 to

$1,940,000.

After careful review of the available data, including the comments

noted above, the FAA has determined that air safety and the public

interest require the adoption of the rule with only editorial changes

and the changes described previously. The FAA has determined that these

changes will neither increase the economic burden on any operator nor

increase the scope of the AD.

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

affected by this AD, that it will take approximately 1.5 work hours per

aircraft to accomplish the required actions, and that the average labor

rate is $60 per work hour. Required parts will cost approximately $298

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

on U.S. operators is estimated to be $1,940,000.

The regulations adopted 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 final

rule does not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is

not a ``significant regulatory action'' under Executive Order 12866;

(2) is not a ``significant rule'' under DOT Regulatory Policies and

Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action

and it is contained in the Rules Docket. A copy of it may be obtained

from the Rules Docket at the location provided under the caption

ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by

reference, Safety.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration amends 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 a new airworthiness directive

to read as follows:

95-01-01 Terra Corporation: Amendment 39-9112. 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 Level) 4 and below; 3-inch ATI-mounted TRT 250 pushbutton

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.

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), Revision 1, dated June 27,

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 been modified in

accordance with the provisions of SB-104, Revision 1, dated June 27,

1994;

(2) An unaffected Terra Corporation transponder; or,

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

Mode S interrogations from both an Air Traffic Control Radio Beacon

System (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,

Revision 1, dated June 27, 1994, perform a ramp test in accordance

with the Testing section of SB-104, Revision 1, dated June 27, 1994.

Conduct the tests and checks required by section 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

that has been modified and tested in accordance with SB-104,

Revision 1, dated June 27, 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 Avionics 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 Airplane Certification Office.

(f) Special flight permits may be issued in accordance with

sections 21.197 and 21.199 of the Federal Aviation Regulations (14

CFR 21.197 and 21.199) to operate the aircraft to a location where

the requirements of this AD can be accomplished.

(g) The modification shall be done in accordance with Terra

Corporation Mandatory Service Bulletin No. SB-104, Revision 1, dated

June 27, 1994. This incorporation by reference was approved by the

Director of the Federal Register in accordance with 5 U.S.C. 552(a)

and 1 CFR part 51. Copies may be obtained from Terra Corporation,

3520 Pan American Freeway NE, Albuquerque, New Mexico, 87107-4796.

Copies may be inspected at the FAA, Office of the Assistant Chief

Counsel, 2601 Meacham Blvd., Room 663, Fort Worth, Texas; or at the

Office of the Federal Register, 800 North Capitol Street, NW., suite

700, Washington, DC.

(h) This amendment becomes effective on February 6, 1995.

Issued in Fort Worth, Texas, on December 21, 1994.

Eric Bries,

Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.

[FR Doc. 94-31903 Filed 12-28-94; 8:45 am]

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