I OPERATING COST I
1.6. IMPACT OF CIVIL AIRWORTHINESS REQUIRE- REQUIRE-MENTS AND OPERATIONAL RULES
1. 6. 1. General
Airworthiness Requirements , Operational Rules and other regulations are framed by national governments and imposed on air-plane manufacturers and operators in order to guarantee the general public a certain level of safety. These rules have a far-reaching influence on the design of the structure, systems, installations , perfor-mance and fly i ng qualities of aircraft . To begin with, the designer will have to make the correct choice of the airworthi-ness code to which the airplane will be de-signed, particularly when an international market is envisaged . He must realize that rules differ from country to country and that distinctions between various airplane categories and types of operation have to be observed. The purpose of this section is to give some insight into the most relevant criteria on which he can base ~is choice . Emphasis will be placed on the following rules:
a. FEDERAL AVIATION REGULATIONS (FAR), issued by the Federal Aviation Administra-tion (FAA), an office of the Department of Transportation of the United States
ofAmer-ica;
b. BRITISH CIVIL AIRWORTHINESS REQUIREMENTS (BCAR) , issued by the Civil Aviation Au-thority (CAA) of Great Britain.
Several other countries have drawn up sim-.
ilar rules , but there are always more or less troublesome differences, leading to confusion and extra costs when an attempt is made t o satisfy different rules simul-taneously. In view of the considerable e-conomi c impact of these requirements, e ·f:-forts have been made and wi ll continue t o be made to arrive at greater uniformity.
In the past the International Civil Aviation Or-ganization (ICAO) has attempted t o promote inter-national r e quirements . . For example, a well-known requirement was ICAO Circular 58-AN/ 53 : "Provision-al Acce ptable Means of Compliance, Aeroplane Per-f o rmanc e", date d 1959. These have not be en gener-ally accepted and only one type of aircraft, the Fokk.er F-27 (Fig. 1-lOa), was certificated
accord-a. A 11large" aircraft: the Fokker F-27 Friendship (Maximum Takeoff Weight 45,000 1b)
b. A " light" aircraft : the Scottish Aviation Jet-stream (Maximum Takeoff weight 12 ,499 lb = 5 ,670 kg) Fig. 1-10. Examples of large and light air-craft
ing to these performance rules, after adoption of the code by the Dutch Civil Aviation Authority (RLD).
In this secti on only those i tems will be reviewed which may affect the design of the
COUNTRY (BUREAU) UNITED STATES OF AMERICA (F .A.A.) GREAT BRITAIN (C.A.A.)
AlRPLAJIES nRFORMANCE GROUP SHALL GENERALLY LIGHT LARGE
LARGE c:aoup
C, ·D, E, A
KAX.. TAKEOFF WEIGHT ' 12,500 LB :S: 12,500 LB
~ 12,500 LB >12,500 LB
NORMAL, UTILITY NON-, SEMI- AND NON-AEROBATIC
CATEGORY ACROBATIC AND NORMAL TRANSPORT AEROBATIC
AGRICULTURAL (RESTR.) AGRICULTURAL
NUtiiER OF ENGINES ONE OR )I)RE TWO OR PI>RE TWO OR HORE ONE OR HORE TWO OR !«JRE
CLASS ALL PROPELLER ALL ALL ALL
TYPE OF ENGINE TYPES* ENGINES ONLY TYPES* TYPES* TYPES*
FLIGHT
HINIHUH ONE OR MORE Tl«l TWO OR N>RE ONE OR I«)RE TWO OR ltJRE
<20 PASS.: NONE <10 PASS.: NONE
CREW CABIN ATTENDANTS NONE ~20 PASS.: ONE $:10 PASS.: ONE -
-OR }I)RE
HAlt. NUMBER OF OCCUPANTS 10 II THRU 23 NOT RESTRICTED
-
NOT RESTRICTEDMAX. OPERATING ALTITUDE 25,000 Fr 25,000 FT NOT RESTRICTED NOT RESTRICTED NOT RESTRICTED
HAl(. DESIGN DIVING SPEED NOT RESTRICTED 300 KTS/H =, 6 NOT RESTRICTED
APPLICABILITY *rec:1procat1ng,turboprops, -Jets and -fans AIRWORTHINESS STANDARDS AIRPLANES
.. ..
ENGINES FAR PART 2] " )) SFAR PART 23 FAR )) FAR PART 25 )) SCAR SECTION K c SCAR SECT lON D " " c" " PROPEUERS " " 35 " " 35 " " 35 " " c " " c
NOISE STANDARDS FAR PART 36 APPENDIX PROP. DRIVEN: F " " )6 -
-GENERAL OPERATING AND FLIGHT RULES FAR PART 91 FAR PART 91 FAR PART 91 LAlD DOWN IN
~ DOMESTIC, FLAG AND SUPPLEMENTAL
-
- FAR PART 121i!i COHH. OPERATORS OF LARGE AIRCRAFT AIR NAVIGATION
;:: AIR TRAVEL CLUBS USING LARGE AIRCRAFT - - FAR PART 12)
~ AIR TAXI AND COHH. OPERATORS FAR PART 135 - REGULATIONS
"
~ AGRICULTURAL AIRCRAFT - - - ' - · FAR PART 1)7-
-Table 1-1. Classification of aircraft categories in the American and British airworthi-ness requirements
aircraft in the preliminary design stage.
Obviously, this summary is not a substi-tute for study and consultation of therel-evant airworthiness requirements. Designers are also advised to take due notice of the FAA Advisory Notes, which are intended as explanatory information to prevent misin-terpretation of the regulations.
Airworthiness requirements sometimes do not cover new developments in civil aviation, while in other cases changes in the
regula-tions are to be expected in the future. All rules are subject to continuous revision and the authorities should be consulted in connection with any particular problem ar-eas that are not covered by current legis-lation. In many cases the design must in-corporate provisions for (retro-)fitting changes which may be required by the regu-lations during development and production and sometimes even after the start of serv-ice.
A choice must be made of the group, cate-gory or class of aircraft to which the de-sign will belong. The upper part of Table 1-1 shows the division of aircraft into groups while the lower part lists the ap-propriate American and British requirement~
The most relevant point to note in this
· table is that civil aircraft are classified as "light" (U.K.) or "small" (U.S.) when their Maximum (certificated) Takeoff Weight is less than 12,500 lb (5, 700 or 5, 760 kg)·.
An impor.tant class of light aircraft is formed by the feeder liners and twin-en-gined business (executive) aircraft of 12,499 lb Maximum ·Takeoff Weight, an ex-ample of which is the Scottish Aviation Jetstream (Fig. 110b). "Large aircraft" for the purpose of airworthiness standards -have a Maximum (certificated) Takeoff Weight of more than 12,500 lb (5,700 or 5,760 kg). The division ·into categories in Table 1-1, as used with respect to certi-fication, indicates a grouping of aircraft
SUB CHAPTER
A
c
D E
CONTENTS
DEFINITIONS AND ABBREVIATIONS
PROCEDURAL RULES: General Rule-making Procedures Enforcement Procedures
Nondiscrimination in Federally As~isted Programs of the FAA AIRCRAFT: Certification Procedures: type 1 production, airworthiness certification,
delegation options, production approval Airworthiness Standards : Airframes: Normal, Utility, Acrobatic Category
airplanes
Transport Category airplanes Normal Category rotorcraft Transport Category rotorcraft Manned Free Balloons
Aircraft Engines Propell~rs Noise Standards: Aircraft type Certification
Technical Standard Orders Authorizations for Materials, Parts, Appliances Airworthiness Directives
Maintenance, Preventive Maintenance, Rebuilding, and Alteration Identification and Registration Marking
Aircraft Registration
Recording of Aircraft Titles and Security Documents AIRMEN: Beyond the scope of this book
AIRSPACE: Designation of Federal Airways, Controlled Airspace and Reporting Points Special Use Airspace .
Establishment of Jet Routes Objects Affecting Navigable Airspace
PART
I II 13 15
21 23 25 27 29 31 33 35
36 37 39 43 45 47 49 61 -67
71 73 75 77 F AIR TRAFFIC AND GENERAL OPERATING RULES:
General Operating and Flight ·Rules 91
Special Air Traffic Rules and Airport Traffic Patterns 93
IFR Altitudes 95
Standard Instrument Approach Procedures 97
Security Control of Air Traffic 99
Moored Balloons, Kites, Transport of Dangerous Articles, Parachute Jumping, G CERTIFICATION AND OPERATIONS: AIR CARRIERS, AIR TRAVEL CLUBS, AND OPERATORS FOR
COMPENSATION OR HIRE:
etc. 101 -107
Certification and Operations: Air Carriers and Conmercial Operators of
Large Aircraft 121
Air Travel Clubs using Large Airplanes 123 of Scheduled Air Carriers with Helicopters 127
Operations of Foreign Air Carriers 129
Rotorcraft External-Load Operations 133
Air Taxi Operators and Cotmnercial Operators 135
Agricultural Aircraft Operations 137
H SCHOOLS AND OTHER CERTIFICATED AGENCIES: Beyond the scope of this book 141-149 I AIRPORTS: Of interest only:
Notice of Construction, Alteration, Activa.J;ion and Deactivation of Airports 157
J AIR NAVIGATION FACILITIES: Beyond the scope of this book 171
K ADMINISTRATIVE REGULATIONS: Beyond the scope of this book 181- 189
Table 1-2. Subdivision of FAR requirements
based upon intended use or operating limi-tations.
1.6.2. Federal Aviation Regulations
The FAA Regulations are divided into Sub-chapters, each containing one group of sub-jects, and these are further subdivided in-to Parts, as exemplified by Table 1-2 .. For
practical purposes, the FAA issues these Parts in a Volume system, each volume con-taining one or more Parts. Subchapters A, C, F and G are of particular interest t0 the designer. It is useful to note the follow-ing distinction:
a. Certification Rules and Procedures (Sub-chapter C), relating to the airworthiness aspects of aircraft, irrespective of the
manner in which they are operated. For ex-ample: rules are established for defining and measuring the landing distance, but no criteria for deciding whether the aircraft can be used on the particular airfields considered are given here.
b. Operating and Flight Rules (Subchapters F and G), specifying conditions to comply with certain types of operations, relating the takeoff and landing distances required to the available runway lengths, etc. Al-though these rules have no direct conse-quence for the airworthiness of a particu-lar type of aircraft, the designer must appreciate the interaction between the Op-erational and Flight Rules in order to de-sign the aircraft so that it fulfils its task. Some examples are given below.
1. Part 121 contains criteria for minimum fuel supply (Pars. 121.639 to 121.647), particularly the reserve fuel required for holding, diversion, etc. of transport air-craft. These rules have a considerable im-pact on payload-range characteristics and hence on operating economy (cf. Section 11. 8).
2. In Paragraphs 121.185 and 121.195 it is stated that upon landing at a destination airport each transport aircraft must come to a full stop within 60% of the effective length of the runway from a point 50 ft (15.24 m) above the runway.
3. Part 135, applicable to Air Taxi Opera-tors and Commercial OperaOpera-tors of small craft, defines a category of "small air-craft" different from the one mentioned previously. This refers to a class of air-planes, operated under an individual exemp-tion and authorizaexemp-tion of the Civil Aero-nautics Board (CAB) or under the exemption authority of the Economic Regulations of Part 298 (Ref. 1-86). In this particular context a "small transport aircraft" means a multi-engined aircraft having a maximum passenger capacity of 30 seats or less or a maximum payload of 7,500 lb (3,400 kg) or under. The operational requirements for this particular category are greatly sim-plified in relation to the transport cat-egory. The British Short SD 3-30 feeder
lin-22
er is an example of an aircraft designed to these particular American regulations.
4. Aircraft with more than 9 passenger seats have to be operated with at least two pilots. When category II operations
(cf. FAR Part 97) or operations in IFR con-ditions are conducted, a second-in-command pilot is also required. Aircraft with 8 passenger seats or less may be operated with a pilot's seat occupied by a passenger if appropriate measures are taken to ensure that the passenger cannot interfere with the pilot's actions. A flight attendant is required when 20 seats or more are in-stalled
1.6.3. British Civil Airworthiness Require-ments
The British Regulations are published in sections which are comparable to the FAR Parts or combinations of Parts. Operating Rules are laid down in separate Air Navi-gation Regulations, which will not be re-viewed here. The subdivision of require-ments according to subjects is compared with the American equivalent in Table 1-3.
SECTION REQUIREMENT AMERICAN EQUIVALENT
A PROCEDURE SUBCHAPTER B
c ENGINE AND PROPELLER PARTS 33 AND 35
D AEROPLANE* PART 25
E GLIDER PART 21 + GLIDER
CRITERIA HANDBOOK G ROTOR CRAFT PARTS 27 AND 29 J ELECTRICAL PARTS 37 AND 41 K LIGHT AEROPLANE PART 23, SFAR PART
23 (PART 135, App. A)
L LICENCING SUBCHAPTER D
R
I
RADIO PARTS 37 AND 41* LARGE AEROPLANES
Table 1-3. Subdivision of BCAR requirements
To the preliminary design engineer of Brit-ish aircraft the following subdivision in-to performance groups is the most signifi-cant:
Group A- aircraft that, following
apower-unit failure, are not forced to land.
Group D - aircratt that, following an en-gine failure, are not forced to landafter takeoff, during initial climb or when fly-ing·on instruments has started.
Group C - aircraft whose performance is not specified with regard to engine failure.
Group E - aircraft for which the extent of performance scheduling is limited (Maximum Takeoff Weight below 6,000 lb or 2,730 kg).
1.6.4. Airworthiness standards and design
The American airworthiness standards FAR Parts 23 and 25 and the BCAR Sections D and K contain several subsections relating to very similar subjects. The FAR is subdi-vided into the following Subparts:
A - general (and definitions) B - flight
c - structures
D - design and construction E
-
powerplant (installation) F - equipment (installation)G - operating limitations (and information)
SUB-PART B. The level of safety intended by the airworthiness regulations will only be achieved by relating the characteristics of the aircraft to those of the airport, the surroundings (obstacles) and the route.
The requirements of this sub-part lay down absolute performance minima, as well as the methodology needed to define and measure flight characteristics.
SUB-PART C defines the loads on the struc-ture, the safety factors, and the minimum strength which shall be provided in the airplane as a whole and in its components.
They are directly related to the primary structure.
SUB-PARTS E AND F. The powerplant and e-quipment installations requirement must en-sure safe operation within the airplane structure during all appropriate phases of the flight.
SUB-PART G. Certain limiting values are to be established, warning notices (placard speeds) displayed, and instructions made available to the flight crew.
The subdivision into "small" or "light"
aircraft on the one hand and "large" air-craft on the other hand is very similar to the subdivision into the non-transport cat-egory and the transport catcat-egory, except that the transport category is not re-stricted in Maximum Takeoff Weight. Some aircraft lighter than 12,500 lb (5,670 kg) have been certificated under FAR Part 25.·
The differences in airworthiness standards for transport and non-transport categories are significant. The main reason for this is that transport aircraft are intended to be operated by airlines, carrying fare0~ paying passengers, while the Other catego-ry is primarily intended for private use by individuals and companies in general avia-tion. The airworthiness authorities assume that, unlike the private owner, the aver-age passenger knows little about flying and relies upon the government to ensure the highest degree of safety in every phase of the flight.
However, to reduce the effects on safety of different certification policies for the two categories, the private aircraft is normally restricted in its operations, es-pecially above congested areas. Besides, a steady improvement in the safety of opera-tion is aimed at for all categories. A small category of light aircraft may carry up to 15-18 passengers and for this cate-gory it has been agreed that the airworthi-ness standards of FAR Part 23 are too low.
The arbitrariness of this subdivision may be demonstrated by Fig. 1-10b, which shows a "light" aircraft and Fig. 1-10a, which shows a "large" aircraft with comparable operational characteristics. Consequently, the FAA has developed a special set of re-gulations, Special FAR Part 23 (SFAR 23), with more stringent performance require-ments, particularly after engine failure
(Ref. 1-78). In order to take advantage of the future growth capacities of an airframe design, a manufacturer may decide to satis-fy certain FAR 25 requirements from the outset, even though the airplane is intended primarily for FAR 23 certification.
23
GENERAL
weight limitation min. number of engines seating capacity
engine failure req.'s in takeoff
accelerate-stop landing
PERFORMANCE wet.runw~y
FLIGHT CHARACTER-ISTICS
STRUCTURAL
climb capability after engine failure lateral e.g. shift minimum control speed
spin characteristics maneuver load factor margin in cruise maneuver and gust
load envelope fatigue evaluation
SFAR
PART 25 PART 23 PART 23
no I ~ 12,500 lb ' I ~ 12,500 lb
two I two I one
no restriction :more than I up to 9 : 10 occupants I I passengers
I I
yes I no I no
complete stop I limited I no
detailed I I limited I > 6000 lb: limited I
I I ~ 6000 lb: no
yes I no I no
I I
throughout flight I takeoff, I I multi-engine:
1landing I limited en-route
included I no I no
related to liftoff speed and stall.
speed
I related to stalling speed at MTOW no
avoid buffet onset
I limited no
1 complete no
fail-safe, safe l~fe1for pressure cabin, wing and fatigue evaluation ,associated structure of major parts 1
DESIGN, fail safe I safe life specified through- I for wing and carry
-CONSTRUCTION __ ~---~----~~----+---o_u_t ________________ ~• _____ t_h_r_o_u_gh __ s_t_r_u_crt_u_r_e ______________ _, bird-proof wiadshield
SYSTEMS, EQUIPMENT
limit descent velocity for landing gear loads max. cabin pressure alt.
after system failure special emergency provisions for pax.
ice protection prov.
restarting capability of engines
powerplants and re la'ted systems system redundancy equipment for adverse weather flight
yes 10 fps 15,000 ft
yes yes
yes complete in<Jependence throughout
yes
no 1depenaent on 1loading, but
no
yes Jlimited
:
yes I complete I independenceno landing wing
~ 10 fps.
I
no
no no no limited independence lessential func- I
ltions duplicated: no
yes no
Table 1-4. Differences in. FAR airworthiness standards for small and transport category airplanes
The most relevant differences between the
transpt,r~ and non-transport categories have been listed in Table 1-4. It should also be
24
noted that transport category aircraft re-quire an approved Flight Manual (FM), con-taining all the necessary information on
performance, operating limitations and procedures, in both normal and emergency situations. Similar documentation for the non-transport category is relatively lim-ited.
Although Table 1-4 applies to the American regula-tions, most of the differences are valid for Brit-ish aircraft as well. Some exceptions are:
1. Section K of the BCAR limits the design dive speed to 300 kts (556 km/h) EAS or H = .6 for take-off weights up to 12,500 lb (5,670 kg).
2. The BCAR Section D is limited to aircraft with a Maximum Takeoff Weight above 12,500 lb (5,670 kg), but may apply to non-transport category aircraft as
well.
3. British light aircraft are divided into perform-ance groups and weight groups, American small air-craft into weight groups only, with some exceptions for Single-engine aircraft.
4. Birdproof windshields are required for both cat-egories of British aircraft, in contrast to American practice, where only transport-category airplanes must be provided with them.
5. British rules are more stringent and detailed with respect to wet runway landing performance cer-tification.
6. Special requirements for British agricultural :::tircraft are included in Section K, while American .3.gricultural aircraft are certificated under re-stricted operations of FAR Parts 21 and 22.
In conclusion, the similarities between the British and American airworthiness stand-ards far outweigh the differences, result-ing in practically the same overall stand-ard of safety, especially for the transport category. The American rules are generally more precise and the designer can apply them more easily without having to consult the authorities. On the other hand, the British rules are more flexible to accommo-date new developments, avoiding special re-gulations. They constitute a basis for the assessment of the airworthiness of a new type of aircraft, the overall .assessment being made on an engineering basis.
It will be clear that several problems have to be solved when certification is intended to comply with both the American and Brit-ish regulations. For example, Ref. 1-80
shows that in the.case of the Beechcraft 99, certificated for several years under FAR Part 23, many performance penalties were imposed when a British certification was applied for. After an extensive revi-sion of the interpretation of the require-ments, the performance figures were less divergent. On the other hand, the Short Skyvan is certificated according to both regulations and exhibits noticeable differ-ences in performance, with the British ver-sion on the conservative side.
There are many important details of air-worthiness which cannot be examined in this chapter. A number of them will be discussed in the appropriate place where they bear directly on the design. This introduction is merely intended to prove that airworthi-ness rules and requirements form a most im-portant source of informatjon for the de-signer and as such should belong to his daily inventory and mental toolkit.