[Federal Register Volume 59, Number 84 (Tuesday, May 3, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-10381]
[[Page Unknown]]
[Federal Register: May 3, 1994]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM-95; Notice No. SC-94-2-NM]
Special Conditions: Learjet Inc., Model 45 Airplane, Lightning
and High-Intensity Radiated Fields
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This document proposes special conditions for the Learjet Inc.
(Lear) Model 45 airplane. This new airplane will utilize new avionics/
electronic systems that provide critical data to the flightcrew. The
applicable regulations do not contain adequate or appropriate safety
standards for the protection of these systems from the effects of
lightning and high-intensity radiated fields. These proposed special
conditions contain the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the existing airworthiness standards.
DATES: Comments must be received on or before June 17, 1994.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Office of the Assistant Chief Counsel,
Attn: Rules Docket (ANM-7), Docket No. NM-95, 1601 Lind Avenue SW.,
Renton, Washington, 98055-4056; or delivered in duplicate to the Office
of the Assistant Chief Counsel at the above address. Comments must be
marked: Docket No. NM-95. Comments may be inspected in the Rules Docket
weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT: Mark Quam, FAA, Standardization
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification
Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056, or
telephone (206) 227-2145.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of
these proposed special conditions by submitting such written data,
views, or arguments as they may desire. Communications should identify
the regulatory docket or notice number and be submitted in duplicate to
the address specified above. All communications received on or before
the closing date for comments will be considered by the Administrator
before further rulemaking action is taken on these proposals. The
proposals contained in this notice may be changed in light of comments
received. All comments submitted will be available in the Rules Docket
for examination by interested persons, both before and after the
closing date for comments. A report summarizing each substantive public
contact with FAA personnel concerning this rulemaking will be filed in
the docket. Persons wishing the FAA to acknowledge receipt of their
comments submitted in response to this notice must submit with those
comments a self-addressed, stamped postcard on which the following
statement is made: ``Comments to Docket No. NM-95.'' The postcard will
be date stamped and returned to the commenter.
Background
On January 27, 1992, Learjet Inc. (Lear), 8220 West Harry Street,
Wichita, KS 67209-2942, P.O. Box 7707, Wichita, KS 67277-7707, applied
for a new type certificate in the transport airplane category for the
Model 45 airplane. The Learjet Model 45 is a T-tail, low wing, medium
sized business jet powered by two Garrett TFE 731-20 turbofan engines
mounted on pylons extending from the aft fuselage. Each engine will be
capable of delivering 3,500 lbs. thrust (3,650 lbs. thrust with auto
performance reserve). The airplane will be capable of operating with
two flight crewmembers and a maximum of ten passengers (standard is
eight passengers).
Type Certification Basis
Under the provisions of Sec. 21.17 of the FAR, Learjet must show,
except as provided in Sec. 25.2, that the Model 45 meets the applicable
provisions of part 25, effective February 1, 1965, as amended by
Amendments 25-1 through 25-75. In addition, the proposed certification
basis for the Model 45 includes part 34, effective September 10, 1990,
plus any amendments in effect at the time of certification; and part
36, effective December 1, 1969, as amended by Amendments 36-1 through
the amendment in effect at the time of certification. The special
conditions that may be developed as a result of this notice will form
an additional part of the type certification basis. In addition, the
certification basis may include other special conditions that are not
relevant to these proposed special conditions.
If the Administrator finds that the applicable airworthiness
regulations (i.e., part 25, as amended) do not contain adequate or
appropriate safety standards for the Learjet Model 45 because of a
novel or unusual design feature, special conditions are prescribed
under the provisions of Sec. 21.16 to establish a level of safety
equivalent to that established in the regulations.
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49 of the FAR after public notice, as required by Secs. 11.28
and 11.29, and become part of the type certification basis in
accordance with Sec. 21.17(a)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design feature, the special conditions would also apply to the
other model under the provisions of Sec. 21.101(a)(1).
Novel or Unusual Design Features
The Model 45 incorporates new avionic/electronic installations,
including primary flight displays, an electronically controlled braking
system, digital electronic engine controls, an engine indication and
crew alerting system (EICAS), multifunction display, and a digital
autopilot/flight director system. These systems may be vulnerable to
lightning and high-intensity radiated fields external to the airplane.
Discussion
The existing lightning protection airworthiness certification
requirements are insufficient to provide an acceptable level of safety
with new technology avionic and electronic systems. There are two
regulations that specifically pertain to lightning protection: one for
the airframe in general (Sec. 25.581), and the other for fuel system
protection (Sec. 25.954). There are, however, no regulations that deal
specifically with protection of electrical and electronic systems from
lightning. The loss of a critical function of these systems due to
lightning would prevent continued safe flight and landing of the
airplane. Although the loss of an essential function would not prevent
continued safe flight and landing, it could significantly impact the
safety level of the airplane.
There is also no specific regulation that addresses protection
requirements for electrical and electronic systems from HIRF. Increased
power levels from ground based radio transmitters and the growing use
of sensitive electrical and electronic systems to command and control
airplanes have made it necessary to provide adequate protection.
To ensure that a level of safety is achieved equivalent to that
intended by the regulations incorporated by reference, special
conditions are proposed for the Lear Model 45, which would require that
new technology electrical and electronic systems be designed and
installed to preclude component damage and interruption of function due
to both the direct and indirect effects of lightning and HIRF.
Lightning
To provide a means of compliance with these proposed special
conditions, clarification of the threat definition of lightning is
needed. The following ``threat definition,'' based on FAA Advisory
Circular 20-136, Protection of Aircraft Electrical/Electronics Systems
Against the Indirect Effects of Lightning, dated March 5, 1990, is
proposed as a basis to use in demonstrating compliance with the
lightning protection special condition, with the exception of the
multiple burst environment, which has been changed to agree with the
latest recommendation from the Society of Automotive Engineers (SAE)
AE4L lightning committee.
The lightning current waveforms (Components A, D, and H) defined
below, along with the voltage waveforms in AC 20-53A, will provide a
consistent and reasonable standard that is acceptable for use in
evaluating the effects of lightning on the airplane. These waveforms
depict threats that are external to the airplane. The effect of these
threats on the airplane and its systems depends upon several factors,
including installation configuration, materials, shielding, airplane
geometry, etc. Therefore, test (including tests on the completed
airplane or an adequate simulation) and/or verified analyses need to be
conducted in order to obtain the resultant internal threat to the
installed systems. The electronic systems may then be evaluated with
this internal threat in order to determine their susceptibility to
upset and/or malfunction.
To evaluate the induced effects to these systems, three
considerations are required:
1. First Return Stroke: (Severe Strike--Component A, or Restrike-
Component D). This external threat needs to be evaluated to obtain the
resultant internal threat and to verify that the level of the induced
currents and voltages is sufficiently below the equipment ``hardness''
level.
2. Multiple Stroke Flash: (\1/2\ Component D). A lightning strike
is often composed of a number of successive strokes, referred to as
multiple strokes. Although multiple strokes are not necessarily a
salient factor in a damage assessment, they can be the primary factor
in a system upset analysis. Multiple strokes can induce a sequence of
transients over an extended period of time. While a single event upset
of input/output signals may not affect system performance, multiple
signal upsets over an extended period of time (2 seconds) may affect
the systems under consideration. Repetitive pulse testing and/or
analysis needs to be carried out in response to the multiple stroke
environment to demonstrate that the system response meets the safety
objective. This external multiple stroke environment consists of 24
pulses and is described as a single Component A followed by 23 randomly
spaced restrikes of \1/2\ magnitude of Component D (peak amplitude of
50,000 amps). The 23 restrikes are distributed over a period of up to 2
seconds according to the following constraints: (1) The minimum time
between subsequent strokes is 10ms, and (2) the maximum time between
subsequent strokes is 200ms. An analysis or test needs to be
accomplished in order to obtain the resultant internal threat
environment for the system under evaluation.
3. Multiple Burst: (Component H). In-flight data gathering projects
have shown bursts of multiple, low amplitude, fast rates of rise, short
duration pulses accompanying the airplane lightning strike process.
While insufficient energy exists in these pulses to cause physical
damage, it is possible that transients resulting from this environment
may cause upset to some digital processing systems.
The representation of this interference environment is a repetition
of short duration, low amplitude, high peak rate of rise, double
exponential pulses that represent the multiple bursts of current pulses
observed in these flight data gathering projects. This component is
intended for an analytical (or test) assessment of functional upset of
the system. Again, it is necessary that this component be translated
into an internal environmental threat in order to be used. This
``Multiple Burst'' consists of repetitive Component H waveforms in 3
sets of 20 pulses each. The minimum time between individual Component H
pulses within a burst is 50 microseconds, the maximum is 1,000
microseconds. The 3 bursts are distributed according to the following
constraints: (1) The minimum period between bursts is 30ms, and (2) the
maximum period between bursts is 300ms. The individual ``Multiple
Burst'' Component H waveform is defined below.
The following current waveforms constitute the ``Severe Strike''
(Component A), ``Restrike'' (Component D), ``Multiple Stroke'' (\1/2\
Component D), and the ``Multiple Burst'' (Component H).
These components are defined by the following double exponential
equation:
i(t)=Io(e-at-e-bt)
where:
t = time in seconds,
i = current in amperes, and
--------------------------------------------------------------------------------------------------------------------------------------------------------
Severe strike Multiple stroke (\1/2\ Multiple burst
(component A) Restrike (component D) component D) (component H)
--------------------------------------------------------------------------------------------------------------------------------------------------------
Io, amp......................................... = 218,810 109,405 54,703 10,572
a, sec-1........................................ = 11,354 22,708 22,708 187,191
b, sec-1........................................ = 647,265 1,294,530 1,294,530 19,105,100
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This equation produces the following characteristics:
ipeak = 200 KA 100 KA 50 KA 10 KA
and,
(di/dt)max(amp/sec) = 1.4 x 1011 1.4 x 1011 0.7 x 1011 2.0 x 1011
= @t=0+sec @t=0+sec @t=0+sec @t=0+sec
(di/dt), (amp/sec) = 1.0 x 1011 1.0 x 1011 0.5 x 1011 ................
= @t=.5s @t=.25s @t=.25s ................
Action Integral (amp2 sec) = 2.0 x 106 0.25 x 106 0.0625 x 106 ................
High-Intensity Radiated Fields (HIRF)
With the trend toward increased power levels from ground based
transmitters, plus the advent of space and satellite communications,
coupled with electronic command and control of the airplane, the
immunity of critical digital avionics systems to HIRF must be
established.
It is not possible to precisely define the HIRF to which the
airplane will be exposed in service. There is also uncertainty
concerning the effectiveness of airframe shielding for HIRF.
Furthermore, coupling of electromagnetic energy to cockpit-installed
equipment through the cockpit window apertures is undefined. Based on
surveys and analysis of existing HIRF emitters, an adequate level of
protection exists when compliance with the HIRF protection special
condition is shown with either paragraphs 1 or 2 below:
1. A minimum threat of 100 volts per meter peak electric field
strength from 10 KHz to 18 GHz.
a. The threat must be applied to the system elements and their
associated wiring harnesses without the benefit of airframe shielding.
b. Demonstration of this level of protection is established through
system tests and analysis.
2. A threat external to the airframe of the following field
strengths for the frequency ranges indicated.
------------------------------------------------------------------------
Average (V/
Frequency Peak (V/M) M)
------------------------------------------------------------------------
10 KHz-100 KHz................................ 50 50
100 KHz-500 KHz............................... 60 60
500 KHz-2000 KHz.............................. 70 70
2 MHz-30 MHz.................................. 200 200
30 MHz-70 MHz................................. 30 30
70 MHz-100 MHz................................ 30 30
100 MHz-200 MHz............................... 150 33
200 MHz-400 MHz............................... 70 70
400 MHz-700 MHz............................... 4,020 935
700 MHz-1000 MHz.............................. 1,700 170
1 GHz-2 GHz................................... 5,000 990
2 GHz-4 GHz................................... 6,680 840
4 GHz-6 GHz................................... 6,850 310
6 GHz-8 GHz................................... 3,600 670
8 GHz-12 GHz.................................. 3,500 1,270
12 GHz-18 GHz................................. 3,500 360
18 GHz-40 GHz................................. 2,100 750
------------------------------------------------------------------------
The envelope given in paragraph 2 above is a revision to the
envelope used in previously issued special conditions in other
certification projects. It is based on new data and SAE AE4R
subcommittee recommendations. This revised envelope includes data from
Western Europe and the U.S.
As discussed above, the proposed special conditions would be
applicable initially to the Learjet Model 45. Should Learjet apply at a
later date for a change to the type certificate to include another
model incorporating the same novel or unusual design feature, these
special conditions would apply to that model as well under the
provisions of Sec. 21.101(a)(1).
Conclusion
This action affects only certain design features on the Learject
Model 45 airplane. It is not a rule of general applicability and
affects only the manufacturer who applied to the FAA for approval of
these features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Federal Aviation Administration,
Reporting and recordkeeping requirements.
The authority citation for these proposed special conditions is as
follows:
Authority: 49 U.S.C. app. 1344, 1348(c), 1352, 1354(a), 1355,
1421 through 1431, 1502, 1651(b)(2), 42 U.S.C. 1857f-10, 4321 et
seq., E.O. 11514; and 49 U.S.C. 106(g).
The Proposed Special Conditions
Accordingly, the Federal Aviation Administration (FAA) proposes the
following special conditions as part of the type certification basis
for the Learjet Model 45 series airplanes.
1. Lightning Protection: (a) Each electrical and electronic system
that performs critical functions must be designed and installed to
ensure that the operation and operational capability of these systems
to perform critical functions are not adversely affected when the
airplane is exposed to lightning.
(b) Each essential function of electrical or electronic systems or
installations must be protected to ensure that the function can be
recovered in a timely manner after the airplane has been exposed to
lightning.
2. Protection from unwanted effects of high-intensity radiated
fields (HIRF). Each electrical and electronic system that performs
critical functions must be designed and installed to ensure that the
operation and operational capability of these systems to perform
critical functions are not adversely affected when the airplane is
exposed to high-intensity radiated fields.
3. For the purpose of these special conditions, the following
definitions apply:
Critical Functions. Functions whose failure would contribute to or
cause a failure condition that would prevent the continued safe flight
and landing of the airplane.
Essential Functions. Functions whose failure could contribute to or
cause a failure condition that would significantly impact the safety of
the airplane or the ability of the flightcrew to cope with adverse
operating conditions.
Issued in Renton, Washington, on April 12, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 94-10381 Filed 5-2-94; 8:45 am]
BILLING CODE 4910-13-M
