would be conducted by the Flight Standardization Board during the test program for airworthiness certification of steep approach capability.
42.4.3 General Criteria.
42.4.3.1 If approval is sought to conduct steep approaches in icing conditions, compliance with the part 25 requirements applicable to steep approach operations identified below should also be shown for icing conditions.
42.4.3.2 The following criteria apply when showing compliance with § 25.125 for steep approaches:
42.4.3.2.1 The airplane should be in the landing configuration used for steep approaches.
42.4.3.2.2 Compliance with the requirement that a stable approach be conducted to a height of 50 feet with a speed not less than VREF (§ 25.125(b)(2)) should be shown with an approach path angle not exceeding the maximum for which approval is sought. The VREF used for steep approaches may be different than the VREF used for normal approaches.
42.4.3.2.3 If the parametric method of determining the landing distance is used (see paragraph 4.11.2.3 of this AC), approach angles should be appropriate to the steep approach path angle desired, and the touchdown sink rate for data expansion should be limited to 6 feet per second.
42.4.3.3 The landing distance established under § 25.125(a) begins at a point 50 feet above the landing surface. If an applicant proposes to use a different height for the beginning of the steep approach landing distance, this must be done through an equivalent level of safety finding, in accordance with § 21.21(b)(1), or an exemption, in accordance with part
11. This has been done in some steep approach certifications to take advantage of precision approach guidance at an airport that guides the airplane to a height over the runway threshold of less than 50 feet.
42.4.3.4 Compliance with §§ 25.119 and 25.121(d) should be shown using the configurations and speeds established for steep approach operations.
42.4.4 Test Conditions for Reasonably Expected Variations in Approach Speed and Path Angle.
The following additional criteria should be applied to show that the airplane is safely controllable and maneuverable during landing (§ 25.143(a)(5)):
42.4.4.1 Under calm air conditions, demonstrate that it is possible to complete an approach, touchdown, and stop without displaying any hazardous characteristics in the following conditions:
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42.4.4.1.1 An approach path angle 2° steeper than the steepest approach path angle for which approval is sought at the VREF established for a steep approach;
and
42.4.4.1.2 The steepest approach path angle for which approval is sought at a speed 5 knots lower than the VREF established for a steep approach.
42.4.4.2 For both conditions in paragraphs 42.4.4.1.1 and 42.4.4.1.2 above:
42.4.4.2.1 The airplane should be loaded to the most critical weight and CG combination;
42.4.4.2.2 The airplane should be in the steep approach configuration;
42.4.4.2.3 The rate of descent should be reduced to no more than 3 feet per second at touchdown;
42.4.4.2.4 Below a height of 200 feet, no action should be taken by the pilot to increase power or thrust, apart from those small changes needed to maintain an accurate approach;
42.4.4.2.5 After initiating the flare, the longitudinal control should not be used to depress the nose apart from those small changes necessary to maintain a continuous and consistent flare flight path;
42.4.4.2.6 The flare, touchdown, and landing should not require exceptional piloting skill, alertness, or strength; and
42.4.4.2.7 To ensure adequate capability for a go-around or down path adjustment, the engines should remain above flight idle power or thrust when stabilized on the approach path.
Note: The 2° steeper approach path angle demonstration is to account for tailwinds on the approach and to take into account necessary corrections back to the desired approach path after inadvertent excursions. The purpose of the test at VREF minus 5 knots is to account for an unnoticed speed decrease during the approach, hence the requirement in paragraph 42.4.4.2.4 for no power or thrust increase to account for the slower speed.
42.4.4.3 For flight test safety reasons, when conducting the 2° steeper approach path angle test condition of paragraph 42.4.4.1.1, the pilot may begin to flare the airplane (or reduce the approach angle) at a reasonable height somewhat higher than the normal steep approach flare height. If this is done, it should be shown by analysis that there is sufficient pitch control to arrest the descent rate if the flare were to be initiated at the normal steep approach flare height, keeping in mind the criteria in paragraphs 42.4.4.2.3 and 42.4.4.2.6.
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42.4.4.4 Compliance with § 25.143(b)(1) should be assessed as follows:
Demonstrate that the airplane can both safely land and safely transition to a go-around following a failure of the critical engine at any point in the approach under the following conditions:
42.4.4.4.1 The steepest approach angle for which approval is sought;
42.4.4.4.2 The VREF established for a steep approach; and
42.4.4.4.3 The most critical combination of weight and CG; and
42.4.4.4.4 For propeller powered airplanes, the propeller of the inoperative engine should be in the position it would normally assume without any action taken by the pilot following an engine failure.
42.4.4.5 The height loss experienced during the maneuver described in paragraph 42.4.4.3 should be determined.
42.4.5 One-Engine-Inoperative Steep Approach.
If approval is sought for one-engine-inoperative steep approach capability, the following criteria should be met at the most critical weight and CG position, using the configuration and speed established for a one-engine-inoperative steep approach:
42.4.5.1 The demonstrations identified in paragraph 42.4.4 above; and
42.4.5.2 Demonstrate that the airplane can safely transition to a go-around during a one-engine-inoperative steep approach.
42.4.6 Airplane Flight Manual.
In accordance with §§ 25.1581, 25.1583, 25.1585, and 25.1587, the following information must be provided in the AFM:
42.4.6.1 Limitations, operating procedures, and performance information necessary for steep approach operations, including the configuration(s), speeds and flight path angle(s) approved for conducting a steep approach; and
42.4.6.2 Operating limitations prohibiting initiation of a steep approach:
42.4.6.2.1 With one engine inoperative, unless the airplane is approved for one-engine-inoperative steep approaches; and
42.4.6.2.2 In forecast or known icing conditions unless the airplane is approved for conducting steep approaches in icing conditions.
42.4.6.3 A statement in the limitations section that the steep approach limitations, procedures, and performance information reflect the capability of the airplane to perform a steep approach, but do not constitute operational approval to conduct steep approach operations.
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42.4.6.4 The height loss determined in accordance with paragraph 42.4.4.4.
42.5 Takeoff and Landing on Unpaved Runways.
42.5.1 Explanation.
There are no specific regulatory requirements or established guidance material pertaining to transport category airplane airworthiness certification for operations on runway surfaces other than smooth and hard. However, several transport category airplanes have been certificated by the FAA for operation on various kinds of unpaved runways, including sod, dirt, and gravel. The following general guidance for airplane certification, for operation on unpaved surfaces, reflects the experience and policy developed during those certification programs.
42.5.2 Procedures.
The considerations described in paragraphs 42.5.2.1 through 42.5.2.6 below should be addressed in obtaining approval for operation of transport category airplanes on unpaved runways.
42.5.2.1 Surface Definition.
Each type of surface should be defined so that it can be recognized, controlled, and maintained in service. The definition should include specification characteristics of the surface necessary for safe operation, such as:
42.5.2.1.1 Surface and sub-base bearing strength, usually expressed in terms of California bearing ratio (CBR). Measurements wet and dry every 500 feet along the runway centerline and 15 to 30 feet either side of the centerline have been used. Other means of defining the suitability of a runway surface to the operation of a particular airplane exist that classify runways based on their load bearing capability; one example is the Aircraft Classification Number (ACN) employed by the International Civil Aviation Organization (ICAO).
42.5.2.1.2 Thickness, aggregate size, and depth of the surface material.
42.5.2.1.3 Presence of rutting.
42.5.2.1.4 Drainage.
42.5.2.1.5 Presence of surface vegetation.
42.5.2.2 Airplane Performance.
If special equipment (e.g., low pressure tires, shields, deflectors) or special procedures are required, the effect of such equipment and/or procedures on airplane performance should be determined and presented in the AFM;
for example, landing gear retraction time may increase if deflectors are 42-12
installed on the landing gear, necessitating changes to AFM first segment climb data.
42.5.2.2.1 Takeoff, accelerate-stop, and landing performance should be demonstrated and scheduled in accordance with the appropriate airworthiness requirements based on each type of unpaved runway surface for which approval is requested. The flight test demonstrations should be conducted on both wet and dry surfaces. An abbreviated series of test conditions, relative to the test requirements of a conventional smooth, hard-surface runway test program, may be acceptable if reliable adjustments for all flap settings can be established to derive these data from the smooth, hard surface performance data. However, a minimum of four conditions each for takeoff, accelerate-stop, and landing should be conducted, and the heaviest weight demonstrated for takeoff and landing will establish the weight limitations for those modes of operation.
42.5.2.2.2 The test runway should be the actual runway for which approval is requested or be chosen to represent the worst characteristics (i.e., high rolling friction, low braking friction, etc.) of each type of unpaved runway for which approval is sought. In this regard, it may not be sufficient to conduct these tests from a runway with a low CBR. Previous tests have shown that rolling friction is primarily a function of CBR, but braking friction is primarily a function of runway surface characteristics and largely independent of CBR and, in some cases, whether the surface is wet or dry. The effects of other variables such as airplane weight and tolerances on recommended tire pressure should also be determined.
42.5.2.2.3 A VMCG demonstration should be conducted. Rudder pedal nose wheel steering may be used, provided the runway surface for the test represents the worst case anticipated for operation. The aerodynamic moment applied to the airplane by the rudder, combined with the use of rudder pedal nose wheel steering, may result in the nose wheel plowing the unpaved runway surface. This can result in the runway surface elements impacting critical airframe and powerplant surfaces. The test should be closely monitored to ensure this damage source does not exist. If the test is conducted with rudder pedal nose wheel steering:
Credit may be taken for any performance benefit provided; and Dispatch without it is prohibited, regardless of whether credit for any performance benefit is taken.
42.5.2.2.4 Landing flare and touchdown characteristics should be evaluated during the landing performance tests.
42.5.2.2.5 Climb performance should account for any additional drag or power/thrust loss due to special equipment installations.
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42.5.2.3 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.
42.5.2.4 Systems, Engine, and Structure.
42.5.2.4.1 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.
42.5.2.4.2 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.
42.5.2.4.3 The effect on landing gear fatigue life, due to operation on unpaved runway surfaces, should be determined.
42.5.2.4.4 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).
42.5.2.5 Maintenance.
42.5.2.5.1 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.
42.5.2.5.2 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 power or 42-14
thrust is set, if those areas may be contaminated with ice or compact snow).
42.5.2.6 Airplane Flight Manual.
42.5.2.6.1 The limitations, procedures, and performance information for unpaved runway operation should be presented in an AFM appendix or supplement.
42.5.2.6.2 The limitations section should include runway surface definitions as established under paragraph 42.5.2.1 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 42.5.2.2 above. 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:
Reduced power or thrust takeoffs are prohibited.
Dispatch with an inoperative anti-skid system is prohibited.
Dispatch with inoperative spoilers/lift dumpers is prohibited.
Use of continuous ignition is required during the takeoff.
42.5.2.6.3 The procedures section should include any special procedures (e.g., use of thrust reversers, nose wheel steering, rolling takeoff, air conditioning/pressurization configuration).
42.5.2.6.4 The performance section should include the performance determined and approved under paragraph 42.5.2.2 above, accounting for any special procedures required. No credit for clearway and/or stopway should be allowed.
42.6 Accounting for Performance Effects of Minor Design Changes and Configuration Deviation List Items.
42.6.1 Explanation.
Minor changes to the type design that involve changes to the exterior of the airplane
(e.g., installation of wing tip-mounted emblem lights) and configuration deviation list (CDL) items (e.g., missing flap hinge covers) have aerodynamic effects and therefore can adversely affect airplane performance. These effects should be assessed and performance decrements identified as applicable.
42.6.2 Procedures.
The methods described below have been found acceptable for assessing the performance decrement that should be applied. These methods are considered as being a conservative alternative to a complete flight test analysis.
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42.6.2.1 Analytically assess the performance degradation of an aerodynamic configuration change by estimating the drag value and then doubling that value. The resulting degradations in takeoff performance, en route climb, and approach/landing climb capability 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 en route 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 or less 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 (in terms of a weight and/or climb gradient capability, as appropriate) should be provided. For design changes, this information should be provided as a limitation in the AFM supplement.
For CDL items, this information should be provided in the CDL appendix, along with the information described under General Limitations in paragraph 42.7.3 of this AC.
42.6.2.2 An alternative method of analytically assessing the performance degradation is to implement conservatism throughout the analysis through conservative round offs and chart readings, using worst-case assumptions, etc. The performance weight decrements are then implemented as noted in paragraph 42.6.2.1 above.
42.7 Configuration Deviation List.
42.7.1 Explanation.
The parts and/or combinations of parts permitted to be missing, and the associated performance decrements and other limitations, must be determined and presented in the AFM CDL.
42.7.2 Procedures.
42.7.2.1 The effect of the missing part should be evaluated to determine if an airplane performance decrement and/or other limitation(s) must be applied to ensure that there is no safety effect. A missing part that affects structural safety, results in damage to other parts, or causes the loss of required safety features is ineligible to be included in the CDL. For example, access panels that, if missing, could affect fire detection, extinguishing, and containment characteristics, are not eligible for listing as CDL items.
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42.7.2.2 Performance decrements should be computed as described in paragraph 42.6 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 different flight phases:
42.7.2.2.1 Only a single performance decrement for takeoff and a single performance decrement for landing will be permitted. For takeoff, the decrement should be the greatest decrement considering takeoff field length, first, second, and final segment climbs, and takeoff flight path. For landing, the decrement should be the greatest decrement considering approach climb, landing climb, and landing field length.
42.7.2.2.2 Only a single weight decrement for the one-engine-inoperative and two-engine-inoperative en route climb performance will be permitted.
42.7.2.2.3 The CDL should contain explanations of the takeoff performance decrement, the landing performance decrement, and the en route performance decrement, as appropriate for the airplane, when the three decrements are used.
42.7.2.3 No reduction in VMO/MMO will be needed if it can be shown by flight test that: (1) no significant changes of flight characteristics or other adverse airworthiness effects exist up to VMO/MMO; and (2) a rational analysis is made for speeds up to VD/MD to show no deterioration of airplane control characteristics. The rational analysis should be based primarily on the proximity of the missing part to aerodynamic surfaces. If a reduction in VMO/MMO is needed, the maximum allowable airspeed indicator and aural warning, required by § 25.1303(b)(1) and (c)(1), must be rescheduled for the reduced speed.
42.7.3 General Limitations.
The following information should be presented in the CDL appendix:
42.7.3.1 When the airplane is operated using the CDL, it must be operated in accordance with the limitations specified in the AFM, as amended in the CDL.
42.7.3.2 Any associated operating limitations (e.g., speed, altitude, or performance limitations) should be listed on a placard affixed in the cockpit in clear view of the pilot in command and other appropriate crewmember(s).
42.7.3.3 For operations using a dispatch or flight release not prepared by the pilot in command, 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.
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42.7.3.4 The operator should list in the airplane logbook an appropriate notation covering the missing part(s) on each flight.
42.7.3.5 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.
42.7.3.6 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.
42.7.3.7 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 lbs, whichever is less, should be applied for takeoff, en route, and landing for each missing part.
42.7.3.8 Takeoff performance penalties should be applied to the takeoff weights that are limited by 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.
42.7.3.9 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.
42.7.3.10 En route performance penalties apply only to operations that are limited by the one- or two-engine(s)-inoperative en route climb performance.
42.7.3.11 The numbering and designation of systems in the CDL appendix should be based on an Air Transport Association (ATA) Specification. The parts within each system should be identified by functional description and, when necessary, by part numbers.
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42.8 Spare Engine Pod.
42.8.1 Explanation.
When a spare engine pod is installed, this is considered a major change to the type design. The airplane’s performance and flight characteristics that are affected by the installation should be evaluated as part of the approval process required by § 21.97(a)(2).
42.8.2 Procedures.
The drag increment due to the spare engine pod installation is normally determined by the drag polar method described in paragraph 4.9.2.1.2 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.
42.9 Authorization for Ferry Flight with One Engine Inoperative—§ 91.611.
42.9.1 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. Section 91.611 also provides performance and operating criteria, including references to sections of part 25 that must be met to obtain a one-engine-inoperative ferry flight permit.
42.9.2 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 42.6 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 42.6. The pertinent regulatory sections are described below.
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42.9.2.1 Section 91.611(a)(2) requires the approved AFM to contain limitations, operating procedures, and performance information, including a description of the configuration of the inoperative propeller (i.e., engine).
42.9.2.2 Section 91.611(c)(1) and (2) require flight tests 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.
42.9.2.3 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.
42.9.2.4 Section 91.611(c)(5) states the airplane must be satisfactorily controllable 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.”
42.9.2.5 Section 25.21(a)(1) states the same allowance for calculated 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 42.6 of this AC should be used.
42.10 Instrument Landing System Weather Minima.
42.10.1 Explanation.
The all-weather categories, as presented by the ICAO, are defined as follows:
42.10.1.1 Category I—200 feet (60 meters) ceiling, 2600 feet (800 meters) runway visual range (RVR).
42.10.1.2 Category II—100 feet (30 meters) ceiling, 1200 feet (400 meters) RVR.
42.10.1.3 Category III.
42.10.1.3.1 Category IIIA—No decision height, 700 feet (200 meters) RVR.
42.10.1.3.2 Category IIIB—No decision height, no external reference and 150 feet (50 meters) RVR.
42.10.1.3.3 Category IIIC—No decision height, no external reference for landing or taxi.
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