Avionics News May 2015 - 13

added to a Part 135 certificate if: (1) they were operating under
an FAA exemption issued prior to March 1, 2007; or, (2) their
current transponder was installed prior to Jan. 1, 1992, provided
that the transponder was manufactured prior to 1990."
The challenge with this guidance is that an aircraft being
operated under Part 91 is not eligible to an FAA exemption
prior to 2007 as suggested in this policy. So the search for
answers began. This is where the documented processes of the
Administrative Procedures Act are used to develop a road map
that either proves the policy is in conflict, or in this case, actually
supports the agency's conclusion.
In order to have a full picture of the requirements, you will
need to review each of the advanced notices of proposed rulemaking, notices of proposed rulemaking and final rules dating
back to 1987. The following is the history of this regulation. You
might care about this explanation as you support your Part 135
customers and their planning during the process of bringing new
aircraft onto their certificates.
Dating back to 1983, the FAA published an ANPRM
announcing its proposal to use Mode S transponders in the
national airspace system. The ANPRM was followed on Sept.
17, 1985, with an NPRM, which, in addition to other changes
within the national airspace system, proposed to formalize the
future use of Mode S transponders. The NPRM was followed
up 17 months later on Feb. 3, 1987, with a final rule (52 FR
3280) that created the air traffic control radar beacon system
and Mode S transponder requirements in the national airspace
system for all aircraft. This final rule replicated the current
language in paragraph 135.143 (c) in Parts 91, 121, 127 and
135, essentially mandating Mode S transponders for all transponder-required aircraft operations.
In 1991, the FAA published a minor change to the air traffic
control radar beacon system and Mode S transponder requirements in the national airspace system, which deleted the requirement that "a non-Mode S transponder installed in an aircraft prior
to July 1, 1992, be manufactured before Jan. 1, 1991." According
to the FAA, "this rule will permit the installation of a non-Mode
S transponder until July 1, 1992, regardless of the date that transponder was manufactured. After July 1, 1992, any transponder
newly installed in an aircraft must be a Mode S transponder."
Again, this reinforced the FAA's intent that all transponders
installed after 1992 be Mode S transponders.
Following significant pressure from the general aviation
community, and the overall lack of the FAA's ability to build
out its surveillance infrastructure, on Aug. 5, 1992, the FAA
published yet another final rule: air traffic control radar beacon
system and Mode S transponder requirements in the national
airspace system (57 FR 34614), "...rescinding the Mode S tran-

sponder requirement for aircraft operating under Part 91 of the
Federal Aviation Regulations."
The comment section of the preamble to this final rule
included answers to questions asked. In particular, "The
commenters believe that the FAA should also rescind
the Mode S transponder installation requirement for aircraft operating under Part 135 of the Federal Aviation
Regulations. They state that the Mode S transponder requirement places an undue financial burden on businesses operating under Part 135." The FAA responded that, "Although
the FAA recognizes this financial burden, it did not propose
to withdraw the Mode S requirement for Part 135 operators because of the need for the enhanced Mode S integrity
in connection with air carrier operations in relatively dense
traffic areas."
This highlighted the agency's intent that the original 1987
rule is intended to apply to Part 135 operators, and that the
1992 rulemaking only exempted Part 91 operators from the
earlier requirement.
In 1996, the FAA reopened the rulemaking with a new NPRM
that proposed 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."
Following the 1996 NPRM, the FAA freely accepted and often
granted exemptions to the Mode S transponder installation
requirements. As a result, the FAA seldom mandated that aircraft
being brought onto a certificate comply with the Mode S transponder mandate, nor apply for an exemption.
After nearly a decade of rulemaking debate, on Oct. 7,
2005, the FAA published two separate notices. First, it finally
closed the 1996 rulemaking with a withdrawal of the proposal. The second notice announced the intent to not grant
any new exemptions to paragraph 135.143 (c) after March 1,
2007. Following the FAA notices, the 2011 InFO clarified the
applicability of section 135.143 (c) toward new aircraft being
brought onto a Part 135 certificate.
As a result of this research, I find no reason to question the
interpretation that aircraft being added to a certificate must
meet the requirements of 135.143 (c), that is any aircraft
brought onto a certificate after Jan. 1, 1992, must have an
appropriate class of TSO-C112 (Mode S) transponder or an
exemption. Aircraft being brought onto a certificate but having been on a different certificate earlier may have a valid
exemption that would still be acceptable.
While this project was specific to transponders, it became an
excellent tutorial in how and why rulemaking is such a precise
exercise that we, as industry, must insist continues. And, oh by
the way Professor Terguson, you were right! q
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