Special Conditions; Cessna Aircraft Company, Model 560 Block Point Change, S.N. 560-0260 and on, Airplanes, Lightning and High- Intensity Radiated Fields (HIRF)

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM-90; Special; Conditions No. 25-ANM-79]

Special Conditions; Cessna Aircraft Company, Model 560 Block

Point Change, S.N. 560-0260 and on, Airplanes, Lightning and High-

Intensity Radiated Fields (HIRF)

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Cessna Aircraft

Company (Cessna), Model 560 Block Point Change, S.N. 560-0260 and on,

airplanes. These new airplanes will utilize new avionics/electronic

systems that perform critical or essential functions. 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 (HIRF). These 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.

EFFECTIVE DATES: March 17, 1994.

FOR FURTHER INFORMATION CONTACT:Mark Quam, FAA, Standardization Branch,

ANM-13, Transport Airplane Directorate, Aircraft Certification Service,

1601 Lind Avenue SW, Renton, Washington, 98055-4056; telephone (206)

227-2145.

SUPPLEMENTARY INFORMATION:

Background

On December 2, 1992, Cessna Aircraft Company (Cessna), applied for

an amended type certificate in the transport airplane category for the

Model 560 Block Point Change, S.N. 560-0260 and on, airplanes. The

Cessna Model 560 Block Point Change is a modified Cessna Model 560. The

two Pratt and Whitney, Canada JT15D-5A engines will be replaced will be

replaced with JT15D-5D turbo fans which will have an increase of

approximately 5 percent thrust. One 8x7-inch primary flight instrument

display (PFD) will be installed at each pilot's station and an 8x7-inch

Multifunction Display (MFD) (without engine indication and crew

alerting system (EICAS)) will be installed in the center panel as

standard equipment. Copilot's standard instruments will be an electro-

mechanical attitude system driven by the VG-14 gyro and an electro-

mechanical horizontal situation indicator (HSI) driven by the C-14D

gyro. An option is offered to replace these copilot instruments with a

copilot's 8x7-inch display. A Honeywell Primus 1000, digital autopilot/

flight director system will be installed. This system will operate in

conjunction with a suite of Collins radios (dual Com, Dual Nav, dual

distance measuring equipment (DME), dual Mode S Transponder, and

automatic direction finder (ADF)). Optional available avionics will be

a second ADF, emergency locator transmitter (ELT) and cockpit voice

recorder (CVR).

The Cessna 560 Block Point Change will also include adhesive bonded

cabin side stringers, rather than riveting. Other structural, thermal

and acoustic improvements will be installed. The zero fuel weight will

increase from 11,200 pounds (lbs.) to 11,700 lbs., the ramp weight will

increase from 16,100 lbs. to 16,500 lbs. and the takeoff weight will

increase from 15,900 lbs. to 16,300 lbs.

Type Certification Basis

Under the provisions of Sec. 21.17 of the FAR, except as provided

in Sec. 25.2, the certification basis of the Model 560 Block Point

Change, S.N. 560-0260 and on, will include the applicable provisions of

Part 25, as amended by Amendments 25-1 through 25-17; Secs. 25.251(e),

25.934, and 25.1091(d)(2) as amended through Amendment 25-23;

Sec. 25.1401 as amended through Amendment 25-27; Sec. 25.1387 as

amended through Amendment 25-30; Secs. 25.787, 25.789, 25.791, 25.853,

25.855, 25.857, and 25.1359 as amended through Amendment 25-32;

Secs. 25.1303(a)(2) and 25.1385(c) as amended through Amendment 25-38;

Sec. 25.305 as amended through Amendment 25-54; Sec. 25.1001 as amended

through Amendment 25-57; Part 34 of the FAR; Part 36 of the FAR as

amended by Amendments 36-1 through 36-18. Also included in the

certification basis are Special Conditions 25-25-CE-4 and 25-ANM-21,

and the special conditions issued herewith.

For the Honeywell Primus 1000, compliance will be shown with the

following regulations: Secs. 25.1301, 25-1303(b), 25.1322 as amended

through Amendment 25-38, Secs. 25-1309, 25.25.1321 (a), (b), (d), and

(e), 25.1331, 25.1333, and 25.1335 as amended through Amendment 25-41.

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 Cessna Model 560 Block Point

Change 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).

Novel or Unusual Design Features

The Model 560 Block Point Change, S.N. 560-0260 and on,

incorporates new avionic/electronic installations, including one 8x7-

inch PFD at each pilot's station, and 8x7-inch MFD (without EICAS) in

the center panel, an optional copilot's 8x7-inch display, a Honeywell

Primus 1000 digital autopilot/flight director system to operate in

conjunction with a suite of Collins radios (dual Com, Dual Nav, dual

DME, and ADF) and optional second ADF. 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 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 could 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, these special

conditions are issued for the Cessna Model 560 Block Point Change, S.N.

560-0260 and on, which require that new technology electronic systems,

such as the primary instrument flight displays, multifunction display,

digital autopilot/flight director, etc., 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 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/Electronic 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. How these threats

affect the airplane and its systems depends upon their installation

configuration, materials, shielding, airplane geometry, etc. Therefore,

tests (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; then

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.

And,

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 subsequent bursts is 30ms,

and (2) the maximum period between subsequent 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) = I o (e-at -- e -bt)

where:

t = time in seconds,

i = current in amperes, and

Multiple stroke

Severe strike Restrike (\1/2\ component Multiple burst

(component A) (component D) D) (component H)

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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

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 = O+sec @t = O+sec @t = O+sec @t = O+sec

di/dt, (amp/sec) = 1.0 x 1011 1.0 x 1011 0.5 x 1011

@t = .5s m>s m>s

Action Integral (amp2 sec) = 2.0 x 106 0.25 x 106 @0.625 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 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.

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Peak (V/ Average

Frequency M) (V/M)

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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

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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.

Discussion of Comments

Notice of Proposed Special Conditions No. SC-93-6-NM for the Cessna

Aircraft Company, Model 560 Block Point Change, S.N. 560-0260 and on,

Airplanes, was published in the Federal Register on November 24, 1993

(58 FR 62051). One comment was received. The commenter (Cessna Aircraft

Company) called to our attention that the description of the avionics

system is different than the configuration being presented for type

certification. They stated that the standard equipment configuration

will have an 8x7-inch PFD at each pilot's station vs the Federal

Register publication description of two PFD's at the pilots station

with an optional copilot PFD. This change was noted and incorporated in

these final special conditions.

Conclusion

This action affects only certain unusual or novel design features

on one model of 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

Air transportation, Aircraft, Aviation safety, Safety.

The authority citation for these 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 Special Conditions

Accordingly, the following special conditions are issued as part of

the type certification basis for the Cessna Aircraft Company, Model 560

Block Point Change, S.N. 560-0260 and on, Airplanes.

1. Lightning Protection: (a) Each new or modified 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 new or modified electronic systems

or installations must be protected to ensure that the essential

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). (a) Each new or modified 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 external to the airplane.

3. For the purpose of these special conditions, the following

definitions apply:

Critical Function. 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 would 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 January 31, 1994

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service, ANM-100.

[FR Doc. 94-3448 Filed 2-14-94; 8:45 am]

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