17194 Federal Register / Vol. 60, No. 65 / Wednesday, April 5, 1995 / Rules and Regulations

113.1(g) and 113.2(a), as published at 60

FR 7862 (February 9, 1995), are effective

as of April 5, 1995.

Dated: March 31, 1995.

Danny L. McDonald,

Chairman, Federal Election Commission.

[FR Doc. 95–8310 Filed 4–4–95; 8:45 am]

BILLING CODE 6715–01–M

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM–105, Special Conditions

No. 25–ANM–97]

Special Conditions: Saab Aircraft AB

Model Saab 2000 Series Airplanes

AGENCY: Federal Aviation

Administration, DOT.

ACTION: Final special conditions.

SUMMARY: These special conditions are

for the Saab Aircraft AB Model Saab

2000 airplane. This airplane will have

novel and unusual design features,

relating to its electronic flight control

system, when compared to the state of

technology envisioned in the

airworthiness standards of part 25 of the

Federal Aviation Regulations (FAR).

These special conditions contain the

additional safety standards which the

Administrator considers necessary to

establish a level of safety equivalent to

that provided by the airworthiness

standards of part 25.

EFFECTIVE DATE: March 29, 1995.

FOR FURTHER INFORMATION CONTACT:

Mark I. Quam, FAA, Standardization

Branch, ANM–113, Transport Standards

Staff, Transport Airplane Directorate,

Aircraft Certification Service, 1601 Line

Avenue SW, Renton, Washington

98055–4056; telephone (206) 227–2145,

facsimile (206) 277–1320.

SUPPLEMENTARY INFORMATION

Background

Special conditions are prescribed

under the provisions of § 21.16 of the

FAR when the applicable regulations for

type certification do not contain

adequate or appropriate standards

because of novel or unusual design

features. The new Saab 2000

incorporates a number of such design

features.

The Saab 2000, certificated on April

29, 1994, is a twin-engined, low-wing,

pressurized turboprop aircraft that is

configured for approximately 50

passengers. The airplane has two

Allison Engine Company AE 2100A

engines rated at 3650 shp. The propeller

is a 6 bladed Dowty Rotol swept shaped

propeller. A single lever controls each

prop/engine combination. An Auxiliary

Power Unit (APU) will be installed in

the tail. The airplane has provisions for

two pilots, an observer, two flight

attendants, overhead bins, a toilet, and

provisions for the installation of a

galley. There is a forward and aft

stowage compartment and an aft cargo

compartment. The airplane has a

maximum operating altitude of 31,000

feet.

The Saab 2000 has a fully

hydraulically powered electronically

controlled rudder and will have fully

hydraulically powered electronically

controlled elevators as a follow-on

design modification. The Powered

Elevator Control System (PECS)

provides control and power actuation of

the left and right elevator surfaces. The

PECS also provides aircraft stability

augmentation and trim functions.

The proposed elevator system is in

many respects similar to the rudder

design and is comprised of a mix of

analog and digital circuitry and has no

mechanical backup. Control columns

are connected to Linear Variable

Differential Transducers (LVDT), stick

damper(s), auto pilot servo, linear

springs with break-outs and are

interconnected with an electronic

disconnect unit.

The position transducers (LVDT),

connected to the control columns,

provide signals to two Powered Elevator

Control Units (PECU). Each PECU

controls two Elevator Servo Actuators

(ESA) through two separate Servo

Actuator Channels (SAC). Each SAC is

subdivided into a primary control lane

and a monitor lane. Two of the four

ESAs, controlled by one PECU,

positions one elevator side.

The ESAs have two modes of

operation, active and damped. The

active mode will result when mode

control current from the PECU and

hydraulic pressure are available. One

active servo actuator is sufficient to

operate the elevator surface.

Elevator Servo Actuators valve and

actuator ram position feedback are

provided by position transducers

(LVDT). The PECUs are connected to

one Flight Control Computer via the

trim relay and two Digital Air Data

Computers. The flight control computer

also provides a signal to the auto pilot

servo.

Stick to elevator gearing is a function

of Indicated Airspeed (IAS). Trim and

stability augmentation are based on IAS,

vertical acceleration and flap position.

Stick, trim and elevator position and

status information are fed to the Engine

Indicating and Crew Alerting System

(EICAS).

Each PECU has built in Automatic

Preflight Built in test (PBIT) and

Continuous Built In Test (CBIT)

circuitry and utilizing cross channel

nomitoring.

The elevator’s actuators are supplied

by three hydraulic circuits that are

physically separated, isolated, fused and

located to minimize common cause

failures. The Number 1 hydraulic circuit

is powered by the left engine and a

backup DC pump and accumulators.

The Number 2 hydraulic circuit is

powered by the right engine and a

backup AC pump and accumulators.

THe Number 3 hydraulic circuit is

powered by an AC drive pump.

The Number 1 hydraulic circuit

powers the left hand (LH) and right

hand (RH) outboard servo actuators. The

Number 2 hydraulic circuit powers the

RH inboard servo actuator. the Number

3 hydraulic circuit powers the LH

inboard servo actuator.

Hydraulic warnings and cautions in

the event of hydraulic supply failure are

provided by the EICAS.

The elevator system is electrically

supported by two system sides, a LH

and a RH side. The electrical system is

normally powered by two AC

generators, each driven by a propeller

gear box. An APU equipped with a

standby generator is installed. When

only one of the three generators is

working, it supplies power to both LH

and RH sides.

Each LH and RH AC system side is

connected via a Transformer Rectifier

Unit (TRU) to a LH and RH DC system

made up of a network of DC buses. A

third center TRU is connected to a

center circuit. The LH, RH and center

buses can be supplied from batteries or

from the TRUs. The center TRU will

replace a failed RH or LH TRU. When

only one TRU unit is working, the LH

and RH buses are tied together with

power being received from the

remaining TRU.

Two DC feeders in addition to two AC

feeders provide power aft of the debris

zone. The LH side is routed through the

ceiling and the RH side is routed

through the floor.

Type Certification Basis

The applicable requirements for U.S.

type certification must be established in

accordance with §§ 21.16, 21.17, 21.19,

21.29, and 21.101 of the FAR.

Accordingly, based on the application

date of June 9, 1989, and Saab Aircraft

AB volunteering for certain later

regulations, the TC basis for the Saab

2000 airplane is as follows:
Federal Register / Vol. 60, No. 65 / Wednesday, April 5, 1995 / Rules and Regulations 17195

Part 25 as amended by Amendments

25–1 through 25–71, except:

§ 25.361 Engine torque, as amended by

Amendment 25–72.

§ 25.365 Pressurized compartment

loads, as amended by Amendment

25–72.

§ 25.571 Damage tolerance and fatigue

evaluation of structure, as amended

by Amendment 25–72.

§ 25.772 Pilot compartment doors, as

amended by Amendment 25–72.

§ 25.773 Pilot compartment view, as

amended by Amendment 25–72.

§ 25.783(g) Doors, as amended by

Amendment 25–72.

§ 25.905(d) Propellers, as amended by

Amendment 25–72.

§ 25.933 Reversing systems, as

amended by Amendment 25–72.

§§ 25.903 and 25.951 as amended by

Amendment 25–73.

§§ 25.851 and 25.854 as amended by

Amendment 25–74.

§ 25.729 as amended by Amendment

25–75.

§ 25.813 as amended by Amendment

25–76.

Part 34, as amended on the date of

issuance of the type certificate.

Part 36, as amended on the date of

issuance of the type certificate.

Special Conditions No. 25–ANM–66,

dated 1/12/93, for Lightning and HIRF

Protection.

Special Conditions No. 25–ANM–82,

dated 3/11/94, for Interaction of

Systems and Structure.

Special conditions, as appropriate, are

issued in accordance with § 11.49 of the

FAR after public notice, as required by

§§ 11.28 and 11.29(b), and become part

of the type certification basis in

accordance with § 21.101(b)(2).

Discussion

Special Conditions No. 25–ANM–82

were written for the rudder and in

anticipation of the installation of the

powered elevator. However, as the Saab

2000 could be flown without rudder

control during certain failure

conditions, and the elevator system was

not installed for initial certification,

Special Conditions No. 25–ANM–82

were limited to requirements common

to both the rudder and follow-on

elevator. The Saab 2000, however,

requires control and power to the

elevator all the time for safe flight and

landing. Therefore, these special

conditions supplement Special

Conditions No. 25–ANM–82 for the

powered elevator. The proposed type

design of the Saab 2000 contains novel

or unusual design features not

envisioned by the applicable part 25

airworthiness standards and therefore

special conditions are considered

necessary in the following areas:

Systems

1. Operation Without Normal

Electrical Power. In the Saab 2000, a

source of electrical power is required by

the elevator electronic flight control

system. Service experience with

traditional airplane designs has shown

that the loss of electrical power

generated by the airplane’s engines is

not extremely improbable. The electrical

power system of the Saab 2000 must

therefore be designed with standby or

emergency electrical sources of

sufficient reliability and capacity to

power essential loads in the event of the

loss of normally generated electrical

power. The need for electrical power for

electronic flight controls was not

envisioned by part 25 since in

traditional designs, cables and

hydraulics are utilized for the flight

control system. Therefore, Special

Condition No. 1 is adopted as proposed.

2. Command Signal Integrity.

Command and control of the control

surfaces will be achieved by fly-by-wire

systems that will utilize electronic (AC,

DC, or digital) interfaces. These

interfaces involve not only the

commands to the control surfaces, but

all the control feedback and sensor

input signals as well. These signal

paths, as well as the electronic

equipment that manages them, can be

susceptible to damage that may cause

unacceptable or unwanted control

responses. The damage may originate

from electrical equipment failures,

mechanical equipment failures or

external damage. Therefore, special

designs are needed to maintain the

integrity of the fly-by-wire interfaces to

an immunity level equivalent to that of

traditional hydro-mechanical designs.

Similar to the conventional steel cable

controls, positioning of the electrical

control equipment and routing of wire

bundles must provide separation and

redundancy to ensure maximum

protection from damage due to a

common cause. Therefore, Special

Condition No. 2 is adopted as proposed.

3. Design Maneuver Requirements. In

a conventional airplane, pilot inputs

directly affect control surface movement

(both rate and displacement) for a given

flight condition. In the Saab 2000, the

pilot provides only one of several inputs

to the control surfaces, and it is possible

that the pilot control displacements

specified in §§ 25.331(c)(1), 25.349(a),

and 25.351 of the FAR may not result

in the maximum displacement and rates

of displacement of the elevator. The

intent of these noted rules may not be

satisfied if literally applied. Therefore,

Special Condition No. 3 is adopted as

proposed.

Discussion of Comments

Notice of Proposed Special

Conditions No. SC–95–1–NM for the

Saab Aircraft AB Model Saab 2000

Series Airplanes was published in the

Federal Register on February 2, 1995

(60 FR 6456). No comments were

received.

Special conditions may be issued and

amended as necessary, as part of the

type certification basis if the

Administrator finds that the

airworthiness standards designated in

accordance with § 21.17(a)(1) do not

contain adequate or appropriate safety

standards because of novel or unusual

design features of an airplane. Special

conditions, as appropriate, are issued in

accordance with § 11.49 after public

notice as required by §§ 11.28 and

11.29(b), effective October 14, 1980, and

will become part of the type

certification basis in accordance with

§ 21.17(a)(2).

Under standard practice, the effective

date of these special conditions would

be 30 days after publication in the

Federal Register. As the intended U.S.

type certification date for the Saab 2000

is April 1, 1995, the FAA finds that

good cause exists to make these special

conditions effective upon issuance.

Conclusion

This action affects only certain

unusual or novel design features on one

model series of airplanes. 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 airplanes.

List of Subjects in 14 CFR Part 25

Air transportation, Aircraft, Aviation

safety, Safety.

The authority citation for these

proposed special conditions is as

follows:

Authority: 49 U.S.C. 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 Saab Aircraft

AB Model Saab 2000 series airplanes.

1. Operations Without Normal Electrical

Power. In lieu of compliance with

§ 25.1351(d), it must be demonstrated by test,

or combination of test and analysis, that the

airplane can continue safe flight and landing

with inoperative normal engine generated

electrical power (electrical power sources

excluding the battery and any other standby

electrical sources). The airplane operation

should be considered at the critical phase of

flight and include the ability to restart the
17196 Federal Register / Vol. 60, No. 65 / Wednesday, April 5, 1995 / Rules and Regulations

engines and maintain flight for the maximum

diversion time capability being certified.

Discussion: The Electronic Flight Control

System installations establish the criticality

of the electrical power generation and

distribution systems, since the loss of all

electrical power may be catastrophic to the

aircraft.

The Saab 2000 fly-by-wire control system

requires a continuous source of electrical

power in order to maintain the flight control

system. The current § 25.1351(d), ‘‘Operation

Without Normal Electrical Power,’’ requires

safe operation in visual flight rules (VFR)

conditions for at least five minutes with

inoperative normal power. This rule was

structured around a traditional design

utilizing mechanical control cables for flight

control while the crew took time to sort out

the electrical failure and was able to reestablish some of the electrical power

generation capability.

In order to maintain the same level of

safety associated with traditional designs, the

Saab 2000 design must not be time limited

in its operation without the normal source of

engine generated electrical power. It should

be noted that service experience has shown

that the loss of all electrical power which is

generated by the airplane’s engines is not

extremely improbable. Thus, it must be

demonstrated that the airplane can continue

safe flight and landing with the use of its

emergency electrical power systems

(batteries, auxiliary power unit, etc.). This

emergency electrical power system must be

able to power loads that are essential for

continued safe flight and landing. Also, the

availability of emergency electrical power

sources, including any credit taken for APU

start reliability, must be validated in a

manner acceptable to the FAA.

The emergency electrical power system

must be designed to supply:

—electrical power required for immediate

safety, which must continue to operate

without the need for crew action following

the loss of the normal electrical power

system;

—electrical power required for continued

safe-flight and landing;

—electrical power required to restart the

engines.

For compliance purposes:

1. A test demonstration of the loss of

normal engine generated power is to be

established such that:

a. The failure condition should be assumed

to occur during night instrument

meteorological conditions (IMC) at the most

critical phase of flight relative to the

electrical power system design and

distribution of equipment loads on the

system.

b. After the unrestorable loss of the source

of normal electrical power, the airplane

engines must be capable of being restarted

and operations continued in IMC until visual

meteorological conditions (VMC) can be

reached. (A reasonable assumption can be

made that turbine engine driven transport

category airplanes will not have to remain in

IMC for more than 30 minutes after

experiencing the loss of normal electrical

power).

c. After 30 minutes of operation in IMC, the

airplane should be demonstrated to be

capable of continuous safe flight and landing

in VMC conditions. The length of time in

VMC conditions must be computed based on

the maximum flight duration capability for

which the airplane is being certified.

Consideration for speed reductions resulting

from the associated failure must be made.

2. Since the availability of the emergency

electrical power system operation is

necessary for safe-flight, this system must be

available before each flight.

3. The emergency electrical power system

must be shown to be satisfactorily

operational in all flight regimes.

2. Command Signal Integrity. In addition to

compliance with § 25.671 of the FAR, it must

be shown that for the elevator Electronic

Flight Control System (EFCS):

(a) Signals cannot be altered

unintentionally, or that the altered signal

characteristics are such that the control

authority characteristics will not be degraded

to a level that will prevent continued safeflight and landing; and

(b) Routing of wire EFCS wires and wire

bundles must provide separation and

redundancy to ensure maximum protection

from damage due to common cause.

Discussion: The Saab 2000 will be using

fly-by-wire (FBW) as a means to command

and control the elevator surface actuators. In

the FBW design being presented, command

and control of the control surfaces will be

achieved by electronic (AC, DC, or digital)

interfaces. These interfaces involve not only

the direct commands to the elevator control

surfaces, but feedback and sensor signals as

well.

Malfunctions could cause system

instabilities, loss of functions or freeze-up of

the control actuator. It is imperative that

after failure at least one path of the

command signal, that is capable of providing

safe flight and landing, remains continuous

and unaltered.

The current regulations, which primarily

address hydro-mechanical flight control

systems, §§ 25.671 and 25.672, make no

specific or implied reference that command

and control signals remain unaltered from

external interferences. Present designs

feature steel cables and pushrods as a means

to control hydraulic surface actuators. These

designs are easily identifiable relative to the

understanding that they are necessary for

safe flight and landing and thus should be

protected and continually inspected.

However, the FBW designs are not easily

discernible from non-essential electronics

where placement of equipment and wire runs

is not critical. Therefore, FBW requires

additional attention when locating the

equipment and wire runs.

It should be noted that:

—The wording ‘‘signals cannot be altered

unintentionally’’ is used in the Special

Condition to emphasize the need for design

measures to protect the FBW control

system from the effects of the fluctuations

in electrical power, accidental damage,

environmental factors such as temperature,

local fires, exposure to reactive fluids, etc.

and any disruptions that may affect the

command signals as they are being

transmitted from their source of origin to

the Power Control Actuators.

3. Design Maneuver Requirements

(a) In lieu of compliance with

§ 25.331(c)(1) of the FAR, the airplane is

assumed to be flying in steady level flight

(point A1 within the maneuvering envelope

of § 25.333(b)) and, except as limited by pilot

effort in accordance with § 25.397(b), the

cockpit pitching control device is suddenly

moved to obtain extreme positive pitching

acceleration (nose up). In defining the tail

load condition, the response of the airplane

must be taken into account. Airplane loads

which occur subsequent to the point at

which the normal acceleration at the center

of gravity exceeds the maximum positive

limit maneuvering factor, n, need not be

considered.

(b) In addition to the requirements of

§ 25.331(c), it must be established that pitch

maneuver loads induced by the system itself

(e.g. abrupt changes in orders made possible

by electrical rather than mechanical

combination of different inputs) are

acceptably accounted for.

Issued in Renton, Washington, on March

29, 1995.

Darrell M. Pederson,

Acting Manager, Transport Airplane

Directorate, Aircraft Certification Service,

ANM–100.

[FR Doc. 95–8371 Filed 4–4–95; 8:45 am]

BILLING CODE 4910–13–M

14 CFR Part 71

[Airspace Docket No. 95–AWA–5]

Modification of the Pensacola

Regional, FL, Lexington Blue Grass,

KY, Fayetteville Regional/Grannis

Field, NC, Pope AFB, NC, and

Providence, Theodore Francis Green

State, RI, Class C Airspace Areas and

Establishment of the Pensacola

Regional, FL, and Providence

Theodore Francis Green State, RI,

Class E Airspace Areas

AGENCY: Federal Aviation

Administration (FAA), DOT.

ACTION: Final rule.

SUMMARY: This rule modifies the Class C

airspace areas at Pensacola Regional, FL,

Lexington Blue Grass, KY, Fayetteville

Regional/Grannis Field, NC, Pope AFB,

NC, and Providence, Theodore Francis

Green State, RI, Airports. This action

modifies the Lexington Blue Grass, KY,

Fayetteville Regional/Grannis Field, NC,

and Pope AFB, NC, airspace

designations to reflect continuous

operation and availability of services.

The effective hours of the Pensacola

Regional, FL, and Providence, Theodore

Francis Green State, RI, Class C airspace

areas are amended to coincide with the

associated radar approach control

facility’s hours of operation. Class C

airspace areas are predicated on an

operational air traffic control tower