Discussion
What Events Have Caused This AD?
The FAA has received information that erroneous altitude resolutions could occur on certain Rockwell Collins TDR-94 and TDR-94D Mode S transponders installed in airplanes with Gillham (gray code) encoded sources. This information indicates that these transponders are utilized in areas with other airplanes equipped with certain aircraft collision avoidance system (ACAS) or traffic alert and collision avoidance system (TCAS) configurations. In these situations, the transponders could receive incorrect TCAS resolution advisories. This could result in a reduction in the intended ACAS or TCAS Change 7 minimum separation margins.
Gillham altitude sources have a 100-foot resolution. The affected transponder will set the altitude resolution status to indicate a 25-foot resolution when connected to a Gillham altitude source. For those units that have digital sources of altitude information, the altitude resolution status is set correctly.
These Rockwell Collins TDR-94 and TDR-94D Mode S transponders could be installed on, but not limited to, the following airplanes:
--Aerospatiale ATR42 series airplanes;
--deHavilland DHC-7 and DHC-8 series airplanes; and
--Short Brothers Models SD3-60 and SD3-60 SHERPA airplanes.
What Is the Potential Impact if FAA Took No Action?
As described above, such erroneous altitude resolutions could cause a reduction in the intended ACAS or TCAS Change 7 separation margins and result in air traffic control or the pilot making flight decisions that put the airplane in unsafe flight conditions.
Has FAA Taken Any Action to This Point?
We issued a proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that would apply to certain Rockwell Collins TDR-94 and TDR-94D Mode S transponders that derive altitude information from a Gillham (gray code) encoded pressure altitude source and are installed on airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on November 5, 2001 (66 FR 55898). The NPRM proposed to require you to have the actions of Rockwell Collins Service Bulletin No. 17 (TDR-94/94D-34-17), dated February 8, 1999, incorporated on any affected Mode S transponder that is installed on a type-certificated airplane where Gillham pressure altitude encoding sources are used.
Was the Public Invited To Comment?
The FAA encouraged interested persons to participate in the making of this amendment. The following presents the comments received on the proposal and FAA's response to each comment:
Comment Issue No. 1: Add Revision 1 of Service Bulletin 17 as an Acceptable Method of Compliance
What Is the Commenter's Concern?
A commenter states that Rockwell Collins Service Bulletin No. 17 (TDR-94/94D-34-17), Revision No. 1, dated May 15, 2000, should be included as an acceptable method of compliance. Thecommenter states that the only change revision 1 makes to the original service bulletin is in the Material Information.
What Is FAA's Response to the Concern?
The FAA concurs that Revision 1 of the service bulletin should be included as an acceptable method of compliance with this AD. We will incorporate this bulletin into the AD.
Comment Issue No. 2: Add Another Service Bulletin as an Acceptable Method of Compliance
What Is the Commenter's Concern?
The commenter states that Rockwell Collins Service Bulletin 20 (TDR-94/94D-34-20), Revision 1, dated May 2, 2001, should also be included as an acceptable method of compliance with this AD. Service Bulletin 20 allows modification of TDR-94 and TDR-94D Mode S Transponders from the -004 or -005 status to the -006 status. Service Bulletin 20 includes all -005 status functionality required in Service Bulletin 17.
What Is FAA's Response to the Concern?
The FAA concurs that Rockwell Collins Service Bulletin 20 (TDR-94/94D-34-20), Revision 1, dated May 2, 2001, should be included as an acceptable method of compliance with this AD. We will incorporate this bulletin into the AD.
FAA's Determination
What Is FAA's Final Determination on This Issue?
After careful review of all available information related to the subject presented above, we have determined that air safety and the public interest require the adoption of the rule as proposed except for the addition of the referenced service information and minor editorial corrections. We have determined that these additions and minor corrections:
--Provide the intent that was proposed in the NPRM for correcting the unsafe condition; and
--Do not add any additional burden upon the public than was already proposed in the NPRM.
Cost Impact
How Many Airplanes Does This AD Impact?
We estimate that 1,400 affected Rockwell Collins TDR-94 and TDR-94D Mode S transponders could be installed on airplanes in the U.S. registry.What Is the Cost Impact of This AD on Owners/Operators of the Affected Airplanes?
We estimate the following costs to accomplish the modification:
Labor cost
Parts cost
Total cost per airplane
Total cost on U.S. operators
3 workhours x $60 per hour = $180
$295
$475
$665,000
The manufacturer will provide warranty credit for parts and labor for work done in accordance with Rockwell Collins Service Bulletin No. 17, dated February 8, 1999, Service Bulletin 17, Revision No. 1, dated May 15, 2000, and to the extent noted in Service Bulletin 20, Revision No. 1, dated May 2, 2001.
Compliance Time of This AD
Why Is the Compliance Time of This AD Presented in Calendar Time Instead of Hours Time-In-Service (TIS)?
The compliance of this AD is presented in calendar time instead of hours TIS because the condition exists regardless of airplane operation. The erroneous altitude indications could occur regardless of the number of times and hours the airplane was operated or the age of the Mode S transponder. For these reasons, FAA has determined that a compliance based on calendar time should be utilized in this AD in order to ensure that the unsafe condition is addressed in a reasonable time period on all airplanes that have an affected Rockwell Collins TDR-94 and TDR-94D Mode S transponder installed, and where Gillham pressure altitude encoding sources are used.
Regulatory Impact
Does This AD Impact Various Entities?
The regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132.
Does This AD Involve a Significant Rule or Regulatory Action?
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 copy of the final 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, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, under 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. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. FAA amends Sec. 39.13 by adding a new AD to read as follows: