277 be on the order of 2.0 to 3.0 percent. On a downhill runway of sufficient magnitude, the airplane could attain a height of 35 feet above the runway and have a positive gradient of climb relative to it, but its flight path may continue to descend beyond that point. The transition from liftoff to climbing flight, in the sense of an ascending flight path, should be adequately addressed with respect to obstacle clearance analysis data.
(2) Minimum Takeoff Climb Gradients. At limiting thrust-to-weight ratios, the transition to free air (i.e., out of ground effect) takeoff climb could result in steep uphill runways rising faster than the airplane’s ability to climb. The minimum second segment takeoff climb gradient should maintain the same margin, relative to the increased maximum uphill runway slope, that exists between the minimum gradient specified in § 25.121 and a two percent uphill runway.
(3) Minimum Approach and Landing Climb Gradients. Balked landing go-arounds, at climb limited landing weights, could also result in an uphill runway rising faster than the airplane’s ability to climb. The minimum approach and landing climb gradients should maintain the same margins, relative to the increased maximum uphill runway slope, that exist between the minimum gradients specified in §§ 25.119 and 25.121 and a two percent uphill runway.
(4) Landing Technique and Distance. Final approaches to steep uphill runways will require early flare initiation, to avoid hard landings, and landing flare air distances will be increased for approaches to steep downhill runways using normal approach descent angles. The AFM operating procedures should describe any special piloting technique required for landing on steep runways. The AFM expansion of landing distances should account for the effect of runway gradient, including any expected increase in flare distances, from 50 feet to touchdown, for steep downhill runways.
(5) Operating Procedures. Operating procedures should be provided in the AFM for operations on runways with gradients greater than ± 2 percent. Guidance should be provided on takeoff rotation and landing flare techniques.
(6) Operational Considerations. For runway slopes greater than ± 3 percent, the specific airport(s) should be investigated relative to runway lengths and surrounding terrain and obstacles. Airport-specific operating limitations may be necessary, such as: direction of takeoff and landing, takeoff flap restrictions, prohibition of overspeed takeoffs on downhill runways, requirement for the antiskid system to be operative and on, and restrictions on engine bleed air and power extraction.
(7) Flight Test Requirements. For approval of certification data for runway slopes exceeding ± 3 percent, operational flight tests should be conducted to verify the proposed procedures and performance information.
231. Criteria For Approval of Steep Approach To Landing.
a. Applicable Regulations . Sections 25.119 & 25.125.
b. Explanation .
(1) Sign Convention. In referring to approach path deviations/increments, a “plus” (or “+”) indicates an increase in the approach path angle (i.e., steeper than) and a “minus” (or “-”) indicates a decrease in the approach path angle (i.e., less steep).
(2) Airworthiness Approval. The standard approach angle certified as part of the type design of transport category airplanes for instrument landing operations is 3 degrees, which coincides with the nominal ILS approach angle. Some ILS installations use a 4.5 degree approach path angle, and a very small number exceed that angle under controlled conditions at dedicated short takeoff and landing (STOL) facilities. Airplanes certificated under part 25, with features that allow them to make steep approaches (greater than 4.5 degrees), and to take off and land in less than normal distances, have not been given credit for this capability by past FAA policies. In response to requests from several operators for authority to conduct steep approaches to short landing fields, the FAA has, however, developed the following basic airworthiness certification criteria for this type of approval. Additions or deletions to these criteria may be required to address specific design features. It should be noted in the AFM that the presentation of the steep approach limitations, procedures, and performance information reflects the capability of the airplane to perform steep approaches, but does not constitute operational approval.
(3) Operational Approval. Operational approval at a particular airport will, in part, be based on the results of the airworthiness testing described in this section. Additional testing, for operational concerns, may be combined with the airworthiness testing.
c. General Requirements .
(1) Approach path guidance should be used for all steep approaches. The landing screen height is 50 feet, unless stated otherwise (see paragraph 231c(3)(c), below).
(2) In lieu of the wind tolerance specified in § 25.21(d), the wind for takeoff and landing performance tests may not exceed 5 knots along the runway, measured at a height of 6 feet above the runway.
(3) In lieu of the corresponding landing performance requirements of § 25.125(a), the horizontal distance necessary to land and come to a complete stop from the landing screen height should be determined (for standard temperatures, at each weight, altitude, and wind within the operational limits established by the applicant for the airplane) as follows:
(a) The airplane should be in the appropriate landing configuration.
(b) A steady approach should be maintained down to the landing screen height at a calibrated airspeed not less than VREF, with an approach path angle not exceeding the maximum for which approval is sought. (VREF is the steady landing approach speed for a defined landing configuration.)
(c) When an approved means of approach path visual guidance is used, and the approach path angle is equal to or greater than 4.5o, the landing screen height may be reduced to 35 feet.
NOTE: An operating limitation in the AFM should specify that when approach path visual guidance is not available, or the approach path angle is less than 4.5o, landing performance must be based on a screen height of 50 feet.
(4) In addition to the approach climb requirements of § 25.121(d) and the landing climb requirements of § 25.119, it should be possible to successfully complete a go-around in the landing configuration, with an engine failure at DH or minimum descent altitude (MDA), as applicable. For propeller driven airplanes, the propeller of the inoperative engine should be in the position it automatically assumes following an engine failure.
(5) If the parametric method is used to determine landing distance, similar to paragraph 19b(3) of this AC, approach angles should be appropriate to the steep approach path angle desired, but the touchdown sink rate for data expansion should be limited to 6 feet per second.
d. Abuse Testing . Under no-wind conditions, it should be demonstrated that it is possible to complete an approach, touchdown, and stop without displaying any hazardous characteristics in the following conditions:
(1) The recommended approach path angle ±2 o at VREF.
(2) The recommended approach path angle at V REF minus 5 knots.
(3) For both conditions d(1) and d(2):
(a) The rate of descent should be reduced to less than 3 feet per second before touchdown.
(b) Below a height of 200 ft. no action should be taken to increase power, apart from those small changes necessary to maintain an accurate approach.
(c) The airplane should be loaded to the critical weight and c.g. combination, and the tests conducted in the all engines operating, or one-engine inoperative, short landing configuration, as appropriate.
(d) During the +2 o approach path abuse demonstration, the engines should remain above idle when stabilized on the approach path.
NOTE: The approach angle abuse requirements are to account for tailwinds or headwinds on the approach and/or to account for necessary corrections back to the desired approach path after inadvert ent excursions. The purpose of the speed abuse test is to account for an unnoticed speed decrease during the approach,
280 hence the requirement in paragraph 231d(3)(b) for no power increase to account for the slower speed.
e. Engine-Out Operation .
(1) It should be shown that the airplane is safely controllable during approach, landing, and during the transition to a go-around, using recommended operational speeds and procedures.
This should be demonstrated after failure of the critical engine, while the airplane is stabilized on VREF at the maximum approved approach path angle, and also at the approved angle plus 2 o.
(2) If the one-engine feathered thrust/drag characteristics are such that it is not possible to maintain the approved approach path angle plus 2 degrees without accelerating, then the airplane should either be able to maintain the approved approach path angle minus 2 degrees at VREF, in the landing configuration with one propeller windmilling (in which case it is permissible to continue the approach), or a go-around should be initiated following any engine failure. The results of this test will determine the appropriate engine-out configuration to be approved in the AFM. If the airplane cannot maintain the approved approach path angle plus 2 degrees with the inoperative engine’s propeller feathered without accelerating, or the approved approach path angle minus 2 degrees with the propeller windmilling, then the AFM limitations section should state that steep approaches are not approved with a failed engine and the airplane must divert to an alternate airport.
NOTE: The intent of this test is to determine an airplane configuration that allows adequate vertical flight path control to permit regaining the approved approach path following deviation from that path for any reason. If an engine failure occurs below DH/MDA, it is permissible to continue the approach with the propeller windmilling, without meeting th e requirements of paragraph e(2), above, provided the airplane is safely controllable during the subsequent approach and landing.
f. Airplane Flight Manual .
(1) Limitations, operating procedures, and performance information necessary for steep approach operations should be clearly identified as such.
(2) The limitations section should note that the limitations, operating procedures, and performance information for steep approach operations are predicated on the use of an approved approach path guidance system.
(3) The limitations section should specify the airplane configurations (i.e., flaps, gear, number of engines operating, etc.) for which steep approach operations are approved.
(4) The landing weight limitations should include the most restrictive of the landing climb performance conditions, as determined by the approach climb requirements of § 25.121(d), the landing climb requirements of § 25.119, and the additional climb requirements specified in paragraph 231c(4) of this AC.
(5) The operating procedures and performance information should clearly identify the airplane configuration, screen height, and approach path angle that the steep approach landing distances are based upon.
(6) The steep approach landing distances should be presented for standard day conditions and should include corrections for weight, altitude, and winds within the limits established for the airplane. Wind velocities should be factored in accordance with § 25.125(f).
At the option of the applicant, corrections may also be presented for non-standard temperatures and runway slope.
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 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
282 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 landi ng 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 V MCG 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 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 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:
1 Reduced 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. Accountability of Performance Degradation Relative to Both Minor Design Changes (External Posture) and Configurat ion 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 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 assess analytically 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, en route 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 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
285 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 234, 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 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) 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 the different flight regimes:
(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.
(2) No reduction in V MO/MMO will be needed if it can be shown by flight test that no significant changes of flight characteristics, or other adverse airworthiness effects exist up to VMO/MMO and a rational analysis is made for speeds up to VD/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 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) The associated 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) 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 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.
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). This requirement implicates all the processes normally associated with part 25 AFM’s.
(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