(v) Climb performance should account for any additional drag or thrust loss due to special equipment installations.
(3) Airplane Handling . Airplane handling characteristics must meet the appropriate airworthiness requirements in each configuration specified for operation. Any special procedures or techniques associated with unpaved runway operation, such as use of thrust reversers, brakes, nose wheel steering, etc., should be identified.
(4) Systems, Engine, and Structure .
(i) It should be demonstrated that systems whose normal functions may be affected by operation from unpaved runways (e.g., anti-skid, nose wheel steering) continue to perform their intended function under all conditions for which approval is requested.
(ii) It should be determined that the airplane can be operated on each defined surface without hazard from likely impingement or engine ingestion of gravel or other surface material. In demonstrating that there is no hazard, consideration should be given to immediate effects such as mechanical damage, and to longer term effects, such as accumulation of loose runway material. These accumulations could cause jamming of flight controls, prevent configuration changes, or cause blockage of cooling ducts or drains. Also, sandblasting effects, from materials thrown by the tires, on the wings, propellers, and fuselage may result in surface erosion that, in time, may lead to more serious structural damage.. To address these concerns, the test airplane, its engines, and any relevant systems should be inspected for surface damage after each accelerate-stop test and each takeoff/landing cycle.
(iii) The effect on landing gear fatigue life, due to operation on unpaved runway surfaces, should be determined.
(iv) It should be demonstrated that any special equipment, such as gravel deflectors or low pressure tires, does not adversely affect any of the AFM performance or ground handling characteristics previously established for the airplane on hard surface runways (e.g., water spray ingestion characteristics of the airplane).
(5) Maintenance .
(i) Any revised airplane maintenance procedures, such as increased frequency of inspections considered necessary to ensure safe operation of the airplane, should be determined and scheduled.
(ii) Runway maintenance procedures specific to the unpaved surface should be determined and scheduled (e.g., grading and sanding at, and just beyond, the touchdown point, and in the area where takeoff thrust is set, if those areas may be contaminated with ice or compact snow).
(6) Airplane Flight Manual (AFM) . The limitations, procedures, and performance information for unpaved runway operation must be presented in an AFM appendix or supplement.
(i) The limitations s ection should include runway surface definitions as established under paragraph (1) above, for which the airplane has been approved to operate and for which suitable performance data has been determined and scheduled in accordance with paragraph (2). Approved airplane configurations, including any special equipment required, along with system limitations, should also be included. The following takeoff and landing limitations should be stated:
(A) Reduced thrust takeoffs are prohibited.
(B) Dispatch with an inoperative antiskid system is prohibited.
(C) Dispatch with inoperative spoilers/lift dumpers is prohibited.
(D) Use of continuous ignition is required during the takeoff.
(ii) The procedures section should include any special p rocedures (e.g., use of thrust reversers, nose wheel steering, rolling takeoff, air conditioning/pressurization configuration).
(iii) The performance section should include the performance determined and approved under paragraph (2) of this section, accounting for any special procedures required. No credit for clearway and/or stopway should be allowed.
235. ACCOUNTABILITY OF PERFORMANCE DEGRADATION RELATIVE TO BOTH MINOR DESIGN CHANGES (EXTERNAL EXPOSURE) AND CONFIGURATION DEVIATION LIST (CDL)ITEMS .
a. Explanation. When minor changes to the type design or a Configuration Deviation List (CDL) item, which have external exposure (e.g., installation of wing tip-mounted emblem lights, missing flap hinge covers, etc.), have been submitted for FAA approval, the consideration of applicable performance degradation has frequently presented a problem. This problem materialized when the assessed performance penalty (in terms of gross weight decrements) was very small and the applicant was of the opinion that the numerical value was so small as to be negligible. However, the resulting Supplemental Type Certificate (STC) usually required an Airplane Flight Manual (AFM) supplement, which contained a performance limitation requiring an applicable gross weight decrement or, in the case of the CDL, a gross weight decrement was listed as a certificate limitation.
b. Procedures . The following criteria were developed with simplicity as a prime objective and yet encompassing a practical resolution of many airworthiness and operational considerations. Some of these considerations were the tolerances applicable to flight test performance data scatter and computerized operational performance/runway planning data, accuracy of AFM performance charts, minimal obstacle clearance climb gradients, as well as weight and balance standard practices.
(1) One method to analytically assess the performance degradation of an aerodynamic configuration change is to estimate the drag value and then increase that by a factor of 2. The resulting degradations in takeoff field length and climb, enroute climb, and approach/landing climb should be determined in terms of airplane weight.
For airplanes with maximum takeoff gross weights not exceeding 20,000 lbs., performance weight decrements less than 0.5 percent of maximum takeoff weight for the takeoff and enroute cases (or 0.5 percent of maximum landing weight for the approach/landing climb cases) may be considered negligible; for airplanes with maximum takeoff gross weights greater than 20,000 lbs., performance weight decrements of 100 lbs. may be considered negligible.
The AFM supplement or CDL appendix should identify those type design changes or CDL items that result in a negligible performance degradation. If the performance degradation is not considered negligible, the appropriate performance penalty should be provided as a limitation in the AFM supplement or in the CDL appendix. Such procedures are considered as being a conservative alternative to a complete flight test analysis. Additionally, the information described under "General Limitations" in paragraph 236, following, should be presented in the CDL appendix.
(2) An alternative method of analytically assessing the performance degradation is to implement conservatism throughout the analysis through conservative roundoffs and chart readings, using worst -case assumptions, etc. The performance weight decrements are then implemented as noted in paragraph (1), above.
236. CONFIGURATION DEVIATION LIST .
a. Explanation. The parts and/or combinations of parts permitted to be missing, and the associated performance decrements and other limitations, shall be determined and presented in the Airplane Flight Manual Configuration Deviation List (CDL).
b. Procedures .
(1) Performance decrements should be computed as described in paragraph 235 of this AC. A single decrement applicable to all AFM performance limitations may be presented; or, subject to the following restrictions, performance decrements may be presented for the different flight regimes:
(i) Only a single performance decrement for takeoff and a single performance decrement for landing will be permitted. For takeoff, the decrement will be the greatest decrement considering takeoff field length, first, second, and final segment climbs, and takeoff flight path. For landing, the decrement shall be the greatest decrement considering approach climb, landing climb, and landing field length.
(ii) Only a single weight decrement for the one-engine-inoperative and two -engine-inoperative enroute climb performance will be permitted.
(iii) The CDL shall contain explanations of the takeoff performance decrement, the landing performance decrement, and the enroute performance decrement, as appropriate for the airplane, when the three decrements are used.
(2) No reduction in VMO/MMO will be required if it can be shown by flight test that no significant changes of flight characteristics, or other adverse airworthiness effects exist up to V MO/MMO and a rational analysis is made for speeds up to V D/MD to show no deterioration of airplane control characteristics. Basis for the rational analysis will primarily be the proximity of the missing part to aerodynamic surfaces. If a reduction in V MO/MMO is required, the maximum allowable airspeed indicator and aural warning, required by §§ 25.1303(b)(1) and (c)(1), must be rescheduled for the reduced speed.
c. General Limitations . The following information shooed be presented in the CDL appendix:
(1) When the airplane is ope rated using the CDL, it must be operated in accordance with the limitations specified in the AFM, as amended in the CDL.
(2) The associated limitations must be listed on a placard affixed in the cockpit in clear view of the pilot in command and other appropriate crewmember(s).
(3) The pilot in command should be notified of each operation with a missing part(s) by listing the missing part(s) in the flight or dispatch release.
(4) The operator should list in the airplane logbook an appropriate not ation covering the missing part(s) on each flight.
(5) If an additional part is lost in flight, the airplane may not depart the airport at which it landed following this event, until it again complies with the limitations of the CDL. This, of course, does not preclude the issuance of a ferry permit to allow the airplane to be flown to a point where the necessary repairs or replacements can be made.
(6) No more than one part for any one system (e.g., one engine pylon fairing) may be missing, unless specific combinations of parts are included in the CDL. Unless otherwise specified, parts from different systems may be missing. The performance penalties are cumulative, unless specifically designated penalties are indicated for the combination of missing parts.
(7) No more than three parts that have each been determined to cause a negligible performance degradation may be missing for takeoff without applying a performance penalty. When more than three such parts are missing, a performance penalty of either 0.5 percent of the maximum takeoff weight or 100 pounds, whichever is less, must be applied for takeoff, en route, and landing for each missing part.
(8) Takeoff performance penalties should be applied to the takeoff weights that are limited b y performance considerations (i.e., takeoff field length, first, second, or final segment climb, or takeoff flight path). If the performance-limited takeoff weight is greater than the maximum certified takeoff weight, the takeoff performance penalties should be applied to the maximum certified takeoff weight to ensure compliance with the noise requirements.
(9) Landing performance penalties should be applied to the landing weights that are limited by performance considerations (i.e., landing field length, landing climb, or approach climb). If the performance-limited landing weight is greater than the maximum certified landing weight, the landing performance penalties should be applied to the maximum certified landing weight to ensure compliance with the noise requirements.
(10) En route performance penalties apply only to operations that are limited by the one- or two-engine(s) inoperative en route climb performance.
(11) The numbering and designation of systems in the CDL appendix is based on Air Transport Association (ATA) Specification 100. The parts within each system are identified by functional description and, when necessary, by part numbers.
237. SPARE ENGINE POD .
a. Explanation. When a spare engine pod is installed, the performance and flight characteristics that are affected by the installation must be evaluated.
b. Procedures . The drag increment due to the spare engine pod installation is normally determined by the drag polar method described in paragraph 17b(1)(ii) of this AC. Check climbs are performed to verify the performance penalties derived from the drag data. These check climbs will normally be conducted in the airplane configuration corresponding to the limiting takeoff performance segment. Performance stalls should be conducted for a minimum of one takeoff and one landing flap setting to determine any effect of the spare engine pod installation on stall speeds and handling characteristics in the stalling maneuver. Vibration and buffeting (§ 25.251), flutter (§ 25.629), and the maximum operating limit speed (§ 25.1505) may also require flight demonstration with the spare engine and pod installed. Longitudinal control (§ 25.145), directional and lateral control (§ 25.147), and ability to trim (§ 25.161) should be demonstrated with the spare engine and pod installed.
238. AUTHORIZATION FOR FERRY FLIGHT WITH ONE ENGINE INOPERATIVE - § 91.611.
a. Explanation. Section 91.611 provides an allowance for the ferry flight of "... a four-engine airplane or a turbine-engine-powered airplane equipped with three engines, with one engine inoperative, to a base for the purpose of repairing that engine...." This allowance is provided for airplanes operated in accordance with Parts 121 and 125 of the FAR. Section 91.611 also provides performance and operating criteria, including references to sections of Part 25, that must be met in order to obtain a one-engine-inoperative ferry-flight permit.
b. Procedures . Section 91.611(a)(1) requires the subject airplane be flight tested to show satisfactory compliance with the requirements of §§ 91.611(b) or (c) for reciprocating and turbine engine powered airplanes, respectively. Deviations from the flight tested configuration may be approved, based on a conservative analysis as described in paragraph 235 of this AC. An example of such a deviation would be a turbojet powered airplane with a one-engine-inoperative ferry flight approval, based on a flight test with the inoperative engine windmilling being subsequently approved for flight with a locked rotor. Though the one-engine-inoperative ferry is an operational approval and not a change in the type design, the airplane performance with the locked rotor should be treated in the same manner as a "Minor Design Change," and the associated drag increment computed conservatively as described in paragraph 235. The pertinent regulatory sections are described below.
(1) Section 91.611(a)(2) requires the approved Airplane Flight Manual (AFM) to contain limitations, operating procedures, and performance information, including a description of the configuration of the inoperative propeller (i.e., engine). This requirement implicates all the processes normally associated with Part 25 AFM's.
(2) Sections 91.611(c)(1) and (2) require flight t ests to be conducted, in the propeller (i.e., engine) configuration desired for approval, to determine takeoff speeds and distances for one-engine-inoperative ferry operations.
(3) Section 91.611(c) refers to the general performance requirements of § 25 .101, the takeoff speed requirements of § 25.107, and the climb requirements of § 25.121, thus tying the one engine inoperative ferry performance to the type design criteria.
(4) Section 91.611(c)(5) states the airplane must be satisfactorily controllab le in a climb with two critical engines inoperative and the climb performance "...may be shown by calculations based on, and equal in accuracy to, the results of testing."
(5) Section 25.21(a)(1), Proof of Compliance, states the same allowance for calcu lated performance if it is "...based on, and equal in accuracy to, the results of testing." Based on this statement, and the previously noted references of § 91.611 to sections of Part 25, it is permissible to calculate one-engine-inoperative ferry performance for a configuration that differs from that flight tested. In such cases the conservative methods described in paragraph 235 of this AC should be used.
239. INSTRUMENT LANDING SYSTEM WEATHER MINIMA .
a. Explanation. The all weather categories, as presented by the International Civil Aviation Organization (ICAO), are defined as follows:
(1) Category I - 200 feet (60 meters) ceiling, 2600 feet (800 meters) runway visual range (RVR).
(2) Category II - 100 feet (30 meters) ceiling, 1200 feet (400 meters) RVR.
(3) Category III
(i) Category IIIA - No decision height, 700 feet (200 meters) RVR.
(ii) Category IIIB - No decision height, no external reference and 150 feet (50 meters) RVR.
(iii) Category IIIC - No decision height, no exter nal reference for landing or taxi.
b. Procedures . The criteria for airworthiness certification of Category II and III all weather operations are contained in Advisory Circular 120-29, "Criteria for Approving Category I and Category II Landing Minima for FAR 121 Operators," dated September 25, 1970, and Advisory Circular 120-28C, "Criteria for Approval of Category III Landing Weather Minima," dated March 9, 1984, respectively.
240. TAKEOFF PERFORMANCE CREDIT FOR ALTERNATE FORWARD CENTER OF GRAVITY LIMITS .
a. Applicable Regulations . Sections 25.23, 25.103, 25.105, 25.107, 25.109, 25.111, 25.113, 25.115, and
25.121 of the Federal Aviation Regulations.
b. Explanation.
(1) In the early 1970s, approvals were granted for one alternate forward center of gravity (c.g.) limit per manufacturer's airplane model (e.g., DC-10 Series 40, B737-300, A300-600, etc.). These approvals included Airplane Flight Manual (AFM) performance information that took credit for the improved takeoff performance available with a further aft forward c.g. limit. The effect of this was that all operators of a manufacturer's airplane model (e.g. B737-300) would have the same alternate forward c.g. limit that may or may not afford any takeoff performance benefit, depending on any one operator's interior configuration, loading, and route structure.
(2) Since those early approvals, the commercial aviation market has changed considerably, with many transport category airplanes capable of fulfilling more than one mission requirement in an operator's fleet. This is particularly true for modern extended range operation two-engine airplanes, most of which were derived from an earlier medium range version of the same basic airplane type. When these airplanes are used in long range operations, the c.g. can be considerably aft of the forward limit, upon which the takeoff performance is based, due to large fuel loadings. The advent of integral horizontal stabilizer fuel tanks has also led to a further aftward shift of the center of gravity. Some operators use these same long range airplanes on short to medium length routes, with the c.g. further forward than that of the long range operations, but still significantly aft of the forward c.g. limit.
(3) The operational flexibility of many o f today's transport category airplanes can be enhanced by taking credit for the improvements in takeoff performance afforded by a c.g. that is aft of the forward limit. The reductions in stall speeds and airplane drag render increased takeoff weights for a given field length and takeoff flight path profile. The approval of takeoff performance for two alternate forward c.g. limits would provide this type of operator with increased flexibility in operating the same airplane model on both long range, and short to medium range routes.
(4) The concept of having alternate forward c.g. limits, with associated improvements in takeoff performance, does not conflict with any of the airworthiness or operational requirements of the Federal Aviation Regulations. Sections 25.103(a)(4) and 25.117 state that compliance with the stall speed and climb performance requirements, respectively, must be shown with the "most unfavorable center of gravity" position. Historically, this has been interpreted as a requirement to conduct the associated performance flight testing at the extreme forward
c.g. limit, and present the resulting AFM performance for that same extreme forward c.g. limit. However, no corresponding requirement exists for presentation of AFM data in § 25.1583 (Operating Limitations) or § 25.1587 (Performance Information) that would limit the performance information to being presented for only the most extreme unfavorable center of gravity obtainable for a particular airplane. In the context of the part 25 airworthiness requirements, it would be acceptable to specify alternate forward c.g. limits as operating limitations, and provide takeoff performance that represents the capability of the airplane at those c.g. limits.
(5) The primary concern in granting pe rformance credit for forward c.g. limits, aft of the extreme forward limit, relates to the diminishment of the conservative performance margin that resulted from generally operating with the c.g. some measurable increment aft of the extreme forward limit, upon which the takeoff performance is based. With the availability of alternate forward c.g. limits, this intrinsic performance margin will be decreased, and on a statistical basis, completely eliminated more often. Consequently, emphasis must be put on maintaining accurate weight and balance records, implementing accurate loading plans, and providing the necessary training and operating procedures for ground and dispatch personnel.
(6) Flight crew training is also a concern for alternate forward c.g. limit operations. With many of today's transport category airplanes incorporating high levels of cockpit automation (e.g., Flight Management Systems), it is imperative that the flightcrew be aware of when an alternate forward c.g. limit is being used as the basis for computing takeoff performance data. This is of critical import when an alternate forward c.g. limit is used in conducting a performance-limited takeoff. Since the aforementioned automated onboard systems may or may not be reprogrammed to accommodate the necessary performance data, it should be emphasized that the forward c.g.
limit provided by the ground operations and dispatch personnel takes precedence over that shown by any onboard systems.
c. Procedures . Approval may be granted for as many as two alternate forward c.g. limits (for a total of three), with associated takeoff performance credit, provided the following certification and operational criteria are complied with:
(1) Certification Criteria .
(i) No more than two alternat e forward c.g. limits (three total) may be approved per operatorspecific variant of a particular airplane type and model. "Airplane type" refers to those airplanes of similar design as identified on the Type Certificate; “airplane model” refers to different versions of an airplane type as reflected on the Type Certificate. An "operator specific variant" is an airplane type and model outfitted to a particular customer's requirements (e.g., engine type, seat pitch, galley locations, etc.). For control purposes, airplanes that are classified as an "operator specific variant" must be clearly identifiable as such; this can be accomplished by definitive AFM document numbering systems and AFM's tied to specific airplane serial numbers.
(ii) The alternate fo rward c.g. limits should be sufficiently different that they will be treated as discrete limits and not result in confusion when determining takeoff performance adjustments.
(iii) The c.g. range that results from the use of an alternate forward c.g. limit must be of sufficient magnitude to be practical and allow for expected variations in operational loading.
(iv) The alternate forward c.g. limits must be identified as such and presented on the Weight and Center of Gravity chart in the limitations section of the basic AFM. That chart should also provide a reference to a separate appendix to the AFM that contains the related airplane performance adjustments.
(v) To minimize the impact on crew training and standardization of cockpit procedures, it is preferable that onboard Flight Management Systems (FMS) be modified to include the performance and fuel management data associated with the alternate forward c.g. limits. If the FMS is not modified in such a manner, a limitation must be added to the AFM that prohibits the use of the FMS when using an alternate forward c.g. limit.
(vi) The AFM performance associated with alternate forward c.g. limit operations must be substantiated by flight test data. This does not mean that flight test data needs to be obtained at every alternate forward c.g. limit; the intent is for the applicant to verify the analytical predictions of c.g. effect with flight test data collected at different c.g.’s.
(vii) All affected cockpit placards and displays must be rev ised to reflect the alternate forward c.g.
limits.
(2) Operational Criteria .
(i) Training and operational procedures, emphasizing the need for accurate weight and balance control, should be implemented. These procedures should address weight and balance knowledge of any given airplane, loading plans and procedures, dispatch responsibilities and procedures, and flightcrew awareness.
(ii) Before an operator implements alternate forward c.g. limit operations, each airplane that will be used in those operations should be weighed and its Operating Empty Weight (OEW) and center of gravity location determined. This process should be repeated on an annual basis to assure accurate knowledge of the empty airplanes’ c.g. positions.
(iii) Operators seek ing takeoff performance credit for alternate forward c.g. limits should provide evidence that their loading plans and procedures result in the c.g. location of any affected airplane being known to within 1 percent mean aerodynamic chord (MAC).
(iv) Operators with mixed fleets of a particular airplane type (i.e., more than one "operator specific variant" of a type) should provide evidence of having an accurate control system to eliminate the potential for loading errors.
(v) If the Flight Management System (FMS) databases have not been modified to reflect the effect of the alternate forward c.g. limits on performance (e.g., takeoff speeds) and fuel consumption, a limitation must be placed in the appropriate operating manuals that prohibits the use of the FMS when operating with an alternate forward c.g. limit.
(vi) All affected documents (Weight and Balance manuals, Flight Crew Operating Manual, etc.)
should be revised to reflect the alternate forward c.g. limits. These documents should also note any restrictions associated with their use.
241. PERFORMANCE CREDIT FOR AUTOMATIC PROPELLER DRAG REDUCTION DEVICES .
a. Explanation. In the description of takeoff path requirements, § 25.111(c)(4) states, in part, that "no change in power or thrust that requires action by the pilot may be made, until the airplane is 400 feet above the takeoff surface." This can result in significant takeoff performance penalties for propeller driven airplanes if the propeller on the critical inoperative engine remains in takeoff pitch, or assumes some other high drag windmilling pitch. Devices that automatically reposition an engine's propeller to a blade angle that reduces its drag contribution
(e.g., autofeather systems), upon failure of the engine, can provide significant takeoff performance gains.
Performance credit has been approved for the operation of these automatic propeller drag reduction devices, below 400 feet above the takeoff surface, when compliance with the criteria described below has been shown.
b. Procedures .
(1) Propeller pitch setting generally has a significant effect on minimum control speeds and airplane drag. The magnitude of these effects is such that continued safe flight may not be possible should a combined failure of an engine and its automatic propeller drag reduction system occur at a takeoff speed based on operation of that system. Consequently, in accord with the stipulations of § 25.1309(b)(1), the probability of this combined failure must be shown to be extremely improbable (on the order of 10 -9 per flight hour).
(2) In determining the combined engine and automatic propeller drag reduction system failure rate of paragraph (1) above, the engine failure rate should be substantiated. Notwithstanding the in-service engine failure rate, the failure of the automatic propeller drag reduction system should be shown not to exceed 10 -4 per flight hour.
(3) The automatic propeller drag reduction system should be designed so that it will automatically be disabled on the operating engine(s) following operation on the failed engine. The probability of an unwanted
operation of the automatic propeller drag reduction system on an operating engine, following its operation on the failed engine, should be shown to be extremely improbable (on the order of 10 -9 per flight hour).
(4) If performance credit is given for operation of the automatic propeller drag reduction system in determining the accelerate-go takeoff distances, the propeller of the failed engine must also remain in the reduced drag position in determining the accelerate-stop distances.
(5) In determining the brake application speed for the maximum energy rejected takeoff demonstration of § 25.109(g), consideration should be given to the accelerate-stop configuration (all-engines-operating vs. engine failure with automatic propeller drag reduction system operation) that will produce the greatest brake energy absorption requirement.
(6) The limitations section of the Airplane Flight Manual should contain a requirement for a flight crew functional check of the automatic propeller drag reduction system. The frequency with which flight crew functional checks and ground maintenance checks of the automatic propeller drag reduction system are required will be considered in the evaluation of the system reliability.
(7) Clear annunciations should be provided to the flight crew for the following:
(i) The automatic propeller drag reduction system is "ARMED."
(ii) A malfunction exists in the automatic propeller drag reductio n system.
242. AIRPLANE BACKING USING REVERSE THRUST .
a. Explanation. Where compliance with applicable airworthiness requirements has been demonstrated, operational approval has been granted for the use of reverse thrust to back airplanes away from airport gates in lieu of a tug pushback. The applicable airworthiness requirements are prescribed in paragraph b, below. Note that compliance with these requirements only demonstrates the capability of the airplane, and does not constitute operational approval; operational approval should be coordinated with the applicable FAA Flight Standards office.
b. Procedures . To obtain airworthiness approval for reverse thrust backing, compliance should be demonstrated with the criteria prescribed below. Since operational approvals for reverse thrust backing specify the applicable airplanes, airports, and gates, some of these tests will be "site" specific and should be coordinated with the applicable FAA Flight Standards office.
(1) Both the airplane and engine manufacturer should determine the applicability of the maneuver and provide appropriate limitations for the procedure. These limitations should include:
(i) Engine power setting and operating parameter limits;
(ii) Minimum and maximum allowable w eights;
(iii) Center of gravity (c.g.) limits;
(iv) Ramp slope limits;
(v) Use of wheel brakes;
(vi) Atmospheric conditions (see NOTE, below); and
(vii) Any other factor unique to the proposed operation.
NOTE: The use of reverse thrust backing with snow, ice, or slush on the ramp, or during periods of heavy rain, is not considered good operating practice.
(2) All limitations, and any normal or abnormal operating procedures, associated with reverse thrust backing should be included in the Airplane Flight Manual (AFM). Any procedures related to ground crew functions should also be included in the AFM.
(3) Testing should be conducted to verify that the reverser efflux does not have a detrimental effect on the powerplant installations. Items to be considered include:
(i) Foreign object damage (FOD);
(ii) Effects on engine cooling;
(iii) Inlet flow distortion;
(iv) Reingestion of exhaust gases; and
(v) Any effects on engine mounted accessories.
(4) Testing shou ld be conducted to verify that the reverser efflux does not have a detrimental effect on other airplane systems such as air conditioning system inlets, APU inlets and exhausts, overboard drains, etc.
(5) It should be verified that cockpit and cabin air will not be contaminated.
NOTE: It is acceptable to have a limitation prohibiting the operation of the air conditioning packs during reverse thrust backing to avoid cockpit and cabin air contamination.
(6) Reverse thrust backing demonstrations should be conducted to evaluate the associated procedures.
These demonstrations should be conducted at:
(i) Maximum ramp weight with the c.g. at the aft limit, and
(ii) Any other weight that may be critical with the c.g. at the aft limit.
(7) The reverse thrust backing demonstrations of paragraph (6), above, should be evaluated to determine:
(i) The degree of aft pitching moment, including its effect on nose wheel steering;
(ii) The effect of inadvertent heavy/emergency braking action;
(iii) Adequate cockpit visibility and ground crew function;
(iv) The adequacy of procedures for transitioning from reverse to forward thrust;
(v) The effect of thrust asymmetry due to failure of an engine to enter reverse, or recover forward thrust mode;
(vi) The effects of low tire pressures;
(vii) The effect of ramp slope and surface condition;
(viii) The effects of ambient atmospheric temperature; and
(ix) The effect of flap/slat configuration.
APPENDIX 1
HISTORY OF JET TRANSPORT PERFORMANCE STANDARDS When the first jet transport airplanes were certificated in the late 1950s, the applicable transport category airworthiness regulations were contained in Part 4b of the Civil Air Regulations (CAR 4b). The airworthiness requirements of CAR 4b were developed from years of experience with propeller-driven airplanes powered by reciprocating engines. The different powerplant operating principles, and expanded speed and altitude envelopes of the first generation jet-powered airplanes required comprehensive changes to the performance requirements of CAR 4b. Special Civil Air Regulation No. SR-422 was adopted in July 1957 as a supplement to CAR 4b, containing airworthiness and operational requirements that were applicable to transport category airplanes powered by turbine engines (turbojet and turbopropeller). As experience was gained, SR-422 was amended in July 1958 (SR-422A) and July 1959 (SR-422B) to better reflect the operating environment of these new airplane designs.
These Special Civil Air Regulations, presented in this appendix, formed the basis for the current transport category airworthiness and operating performance regulations of 14 CFR parts 25, 121, and 135. Though the number of operational airplanes that were certificated to these requirements is continually decreasing, these Special Civil Air Regulations, and the related preamble material, still provide a worthwhile perspective on many of the issues behind the development of today ’s regulations, and are therefore preserved for future reference in this appendix.
SPECIAL CIVIL AIR REGULATION NO. SR-422 Effective: August 27, 1957 Adopted: July 23, 1957 Turbine-Powered Transport Category Airplanes of Current Design Part 4b of the Civil Air Regulations contains rules governing the design of transport category airplanes. For a number of years, this part has established airworthiness requirements for this category of airplanes by prescribing detailed provisions to be met for the issuance of a type certificate. However, the advent of turbine-powered airplanes (jets, turbo-props, etc.) has brought about operations at considerably higher speeds and altitudes than those involving reciprocating engine airplanes. These higher speeds and altitudes as well as certain inherent characteristics of turbine engines have introduced numerous new technical and design problems and have necessitated re-evaluation and amendment of many provisions in Part 4b.
In recent years the Board has amended Part 4b by introducing numerous technical provisions more specifically applicable to turbine-powered airplanes. These were included in amendments pertaining to structural, flight characteristic, powerplant installation, and other provisions. It is believed that Part 4b as now written is applicable to turbine-powered airplanes with but one exception; namely, airplane performance. In the future, further amendments to this part, other than those relating to performance, will be comparatively minor in nature mainly reflecting the latest experience in the certification and operation of these airplanes.
The performance requirements presently in Part 4b were first promulgated almost twelve years ago. They are now considered by the Board to be in a form not suitable for direct application to turbine-powered airplanes.
The administrator of Civil Aeronautics is in receipt of a large number of applications for type certification of turbine-powered airplanes. However, the so-called "non-retroactive" clause of section 4b.11(a) of Part 4b does not make applicable to a particular airplane type any amendment which is adopted after an application is filed by the manufacturer for type certification of that airplane. Thus, most of these airplanes are not now required to meet some of the latest effective provisions of Part 4b unless the Board prescribes otherwise. With so many applications for type certificates pending, it is essential that the Board establish adequate requirements which will effectively apply to the type certification of turbine-powered transport category airplanes. This Special Civil Air Regulation is being promulgated for that purpose.
This Special Civil Air Regulation is being made effective with respect to all turbinepowered transport category airplanes not yet certificated. In essence, it prescribes a revised set of performance requirements for turbine-powered airplanes and incorporates such of the recent amendments to Part 4b as the Administrator finds necessary to insure that the level of safety of turbine-powered airplanes is equivalent to that generally intended by Part 4b.
The performance requirements contained herein include not only the performance requirements necessary for the certification of an airplane, but also the complementary performance operating limitations as applicable under Parts 40, 41, and 42 of the Civil Air Regulations. In promulgating this new performance code, the Board intends that the resulting level of safety will be generally similar to the level of safety established by the performance code as expressed by the provisions now contained in Parts 4b and 40 (or 41 or 42 as appropriate) for reciprocating engine airplanes. To attain this, many of the performance provisions have been modified for better applicability to turbine-powered airplanes, some in the direction of liberalization, others in the direction of improvement in the required performance.
A significant change being made is the introduction of full temperature accountability in all stages of performance, except the landing distances required. The introduction of full temperature accountability will insure that the airplane's performance is satisfactory irrespective of the existing atmospheric temperature. The performance requirements heretofore applicable did not give sufficient assurance in this respect.
The reason for omitting the direct application of temperature accountability in the requirement for landing distances is that this stage of performance always has been treated in a highly empirical fashion whereby temperature effects are taken into account indirectly together with the effects of other operational factors. Long range studies on rationalization of airplane performance so far have not yielded a satisfactory solution to the landing stage of performance.
The Board hopes, however, that continued studies will result in a solution of this problem in the near future.
The introduction of full temperature accountability has necessitated a complete reevaluation of the minimum climb requirements. Since the prescribed climb must now be met at all temperatures rather than to be associated with standard temperature, the specific values of climb have been altered. In each instance, the change has been in the downward direction because, although the previous values were related to standard temperature, a satisfactory resultant climb performance was attained at temperatures substantially above standard. While values of minimum climb performance specified in the new code will tend to increase the maximum certificated weights of the airplane for the lower range of temperatures, they will limit these weights for the upper range of temperatures, giving adequate assurance of satisfactory climb performance at all temperatures.
In considering the various stages of flight where minimum values of climb have been heretofore established, the Board finds that in two of the stages (all-engines-operating en route and one-engine-inoperative en route) the establishment of minimum values of climb is unnecessary because, in the case of the all-engines-operating stage, it has been found not to be critical and the case of the one-engine-inoperative stage is now more effectively covered by the en route performance operating limitations.
Considering that the minimum climbs being prescribed affect mainly the maximum certificated weights of the airplane but not the maximum operating weights, the Board, in adopting the new performance code, places considerable emphasis on the ability of the airplane to clear obstacles on take-off and during flight. To this end, criteria for the take-off path, the en route flight paths, and the transition from take-off to the en route stage of flight have been prescribed to reflect realistic operating procedures. Temperature is fully accounted for in establishing all flight paths and an expanding clearance between the take-off path and the terrain or obstacles is required until the en route stage of flight is reached.
In order to insure that the objectives of the prescribed performance are in fact realized in actual operations, the manufacturer is required to establish procedures to be followed in the operation of the airplane in the various conditions specified in the regulation. These procedures, each designed for a specific airplane, will permit the operator to utilize the full performance capabilities of the airplane more readily than if the regulations prescribed all-inclusive procedures. The use of these procedures in determining compliance with the requirements governing take-off, en route, and landing stages, will also add considerable flexibility to the regulation.
The new performance requirements established more clearly than heretofore which of the performance limitations are conditions on the airworthiness certificate of the airplane. In addition to the maximum certificated take-off and landing weights, there are included limitations on the take-off distances and on the use of the airplane within the ranges of operational variables,