(d) 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.
(3) The height loss experienced during the maneuver described in paragraph 231d(2) should be determined.
e. One-Engine-Inoperative Steep Approach.
(1) If approval is sought for one-engine inoperative steep approach capability, the following criteria should be met at the most critical weight and c.g. position, using the configuration and speed established for a one-engine-inoperative steep approach:
(a) The demonstrations identified in paragraph 231d(1) above; and
(b) Demonstrate that the airplane can safely transition to a go-around during a one-engine inoperative steep approach.
f. Airplane Flight Manual.
(1) In accordance with §§ 25.1581, 25.1583, 25.1585, and 25.1587, the following information must be provided in the AFM:
(a) 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
(b) Operating limitations prohibiting initiation of a steep approach:
1 With one engine inoperative, unless the airplane is approved for oneengine inoperative steep approaches; and
2 In forecast or known icing conditions unless the airplane is approved for conducting steep approaches in icing conditions.
(c) 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.
(d) The height loss determined in accordance with paragraph 231d(3).
232. Takeoff and Landing On Unpaved Runways.
a. Explanation. There are no specific regulatory requirements or established guidance material pertaining to transport category airplane airworthiness certification for operations on
301 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.
b. Procedures. The considerations described in paragraphs (1) through (6), below, should be addressed in obtaining approval for operation of transport category airplanes on unpaved runways.
(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:
(a) 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).
(b) Thickness, aggregate size, and depth of the surface material.
(c) Presence of rutting.
(d) Drainage.
(e) Presence of surface vegetation.
(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 installed on the landing gear, necessitating changes to AFM first segment climb data.
(a) 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.
(b) 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.
(c) 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:
1 Credit may be taken for any performance benefit provided; and
2 Dispatch without it is prohibited, regardless of whether credit for any performance benefit is taken.
(d) Landing flare and touchdown characteristics should be evaluated during the landing performance tests.
(e) Climb performance should account for any additional drag or power/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.
(a) 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.
(b) 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.
(c) The effect on landing gear fatigue life, due to operation on unpaved runway surfaces, should be determined.
(d) 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.
(a) 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.
(b) 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 thrust is set, if those areas may be contaminated with ice or compact snow).
(6) Airplane Flight Manual. The limitations, procedures, and performance information for unpaved runway operation should be presented in an AFM appendix or supplement.
(a) The limitations section 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) 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:
304 1 Reduced power or thrust takeoffs are prohibited.
2 Dispatch with an inoperative antiskid system is prohibited.
3 Dispatch with inoperative spoilers/lift dumpers is prohibited.
4 Use of continuous ignition is required during the takeoff.
(b) The procedures section should include any special procedures (e.g., use of thrust reversers, nose wheel steering, rolling takeoff, air conditioning/pressurization configuration).
(c) The performance section should include the performance determined and approved under paragraph (2) above, accounting for any special procedures required. No credit for clearway and/or stopway should be allowed.
233. Accounting for Performance Effects of Minor Design Changes and Configuration Deviation List (CDL) Items.
a. 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.
b. 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.
(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 234 of this AC.
(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 (1), above.
234. Configuration Deviation List.
a. 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.
b. Procedures.
(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.
(2) Performance decrements should be computed as described in paragraph 233 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:
(a) 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.
(b) Only a single weight decrement for the one-engine-inoperative and twoengine-inoperative en route climb performance will be permitted.
(c) 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.
(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.
c. General Limitations. The following information should be presented in the CDL appendix:
(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.
(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).
(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.
(4) The operator should list in the airplane logbook an appropriate notation 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, should 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 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.
(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 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.
235. Spare Engine Pod.
a. 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).
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)(b) 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.
236. 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. 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 233 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 233. The pertinent regulatory sections are described below.
(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).
(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.
(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 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.”
(5) Section 25.21(a)(1), “Proof of Compliance,” 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 233 of this AC should be used.
237. Instrument Landing System Weather Minima.
a. Explanation. The all weather categories, as presented by the 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.
(a) Category IIIA - No decision height, 700 feet (200 meters) RVR.
(b) Category IIIB - No decision height, no external reference and 150 feet (50 meters) RVR.
(c) Category IIIC - No decision height, no external reference for landing or taxi.
b. Procedures. The criteria for airworthiness certification of Category I and II all weather operations are contained in AC 20-129A, “Criteria for Approval of Category I and Category II Weather Minima for Approach,” dated August 12, 2002. The criteria for airworthiness certification of Category III all weather operations are contained in AC 20-128D, “Criteria for
309 Approval of Category III Weather Minima for Takeoff, Landing, and Rollout,” dated July 13, 1999.
238. 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.
b. Explanation.
(1) In the early 1970’s, approvals were granted for one alternate forward c.g. (c.g.)
limit per manufacturer’s airplane model (e.g., DC-10 Series 40, B737-300, A300-600, etc.).
These approvals included 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 particular airplane model (e.g., B737-300) would have the same alternate forward
c.g. limit, which may or may not be useable by any particular operator, depending on that 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 airplane type. When these airplanes are used in long range operations, the c.g. can be considerably aft of the forward limit due to large fuel loadings. The advent of integral horizontal stabilizer fuel tanks has also led to a further shift aft of the c.g.. 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 of 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 result in 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 operators with increased flexibility in operating the same airplane model on both long 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. Section 25.103(b)(5) requires stall speeds to be based on the c.g. position that results in the highest value of reference stall speed. Section
25.117 states that compliance with the climb performance requirements must be shown with the “most unfavorable c.g.” position. Historically, this has been interpreted as a requirement to conduct the associated performance flight testing at the most forward c.g. limit, and present the resulting AFM performance for that same extreme forward c.g. limit. However, there is no requirement that prevents operating limitations from being used to establish multiple forward c.g.
limits.
(5) The primary concern in granting performance credit for forward c.g. limits that are aft of the extreme forward limit, is the reduction in the conservative performance margin that results from usually operating with the c.g. aft of the extreme forward limit that the takeoff performance is based on. With the availability of alternate forward c.g. limits, this safety margin will be decreased, and on a statistical basis, completely eliminated more often. Consequently, emphasis should 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, it is important 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 most important when an alternate forward c.g. limit is used in conducting a performance-limited takeoff.
c. Procedures. Approval may be granted for as many as two alternate forward c.g. limits (for a total of three forward c.g. limits), with associated takeoff performance data, using the following certification criteria:
(1) No more than two alternate forward c.g. limits (three total) should be approved per operator-specific 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” should be clearly identifiable as such; this can be accomplished by definitive AFM document numbering systems and AFM’s tied to specific airplane serial numbers.
(2) The alternate forward 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.
(3) The c.g. range that results from the use of an alternate forward c.g. limit should be of sufficient magnitude to be practical and allow for expected variations in operational loading.
(4) The alternate forward c.g. limits should be identified as such and presented on the weight and c.g. 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.
(5) To minimize the impact on crew training and standardization of cockpit procedures, onboard systems that use or provide weight and balance information (e.g., Flight Management Systems, Electronic Flight Bags, etc.) should include the performance and fuel management data associated with the alternate forward c.g. limits. If they do not include such information, a
311 limitation should be added to the AFM that prohibits the use of such systems when using an alternate forward c.g. limit.
(6) The AFM performance associated with alternate forward c.g. limit operations must be substantiated by flight test data per § 25.21(a)(2). 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.
(7) All affected cockpit placards and displays should be revised to reflect the alternate forward c.g. limits.
239. 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:
(a) Engine power or thrust setting and operating parameter limits;
(b) Minimum and maximum allowable weights;
(c) C.g. limits;
(d) Ramp slope limits;
(e) Use of wheel brakes;
(f) Atmospheric conditions (see NOTE below); and
(g) 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.