25 1 . In § 23.221(a)(2)(ii), "with the ailerons deflected opposite the direction of turn in the most adverse manner" means anti-spin or "reflexive" ailerons.
2 . In § 23.221(a)(2)(ii), "respond immediat ely" means recovery in approximately one-quarter turn or that amount that the test pilot determines is immediate and repeatable.
3 . The preceeding spin test guidance does not reduce the regulatory burden to show that it is “impossible to obtain” an unrecoverable spin for a given airplane design. The manufacturer is responsible for compliance with the regulations and should perform a thorough spin test evaluation. This AC simply describes a methodology that the FAA has found is adequate for a showing of compliance to the spin requirements for small, simple, low performance airplanes.
Finding literal compliance to the regulation that states “… it must be impossible to obtain unrecoverable spins…” is not practical since this would necessitate an infinite number of test points.
The methods described have been found to be an adequate number of test points to find compliance for these airplanes. This is derived from experience, technical data, and judgment, through many years using AC 23-8A for showing compliance on more complex airplanes. The methodology in this AC is a refinement of the method in AC 23-8A for showing compliance to the spin requirement of 23.221(a)(1)(iii) for these simple airplanes.
k. Emergency Landing Dynamic Conditions .
(1) Regulations Reference . Section 23.562.
(2) Discussion .
(a) See AC 23.562-1 “Dynamic Testing of Pa rt 23 Airplane Seat Restraint Sy stems and Occupant Protection” for information. AC 23.562-1 addresses all part 23 airplanes, and has no specific guidance for “small, simple, low performance airplanes”. However, all of the guidance material may be applied to “small, simple, low performance airplanes”.
(b) See AC 23-11A “14 CFR Part 23 Type Certif ication of an Airplane Originally Certificated to Joint Aviation Regulations - Very Light Airplane (JAR-VLA) Standards”. Some small, simple, low performance airplanes, are similar to the JAR-VLA discussed in AC 23-11A, and therefore, that AC's guidance material may be of interest to the reader.
l. Fabrication Methods .
(1) Regulation Reference . Section 23.605.
(2) Process Specifications Format . The following sample process specification (for welding) provides an acceptable format. An applicant may develop specifications in this format.
(a) 1.0 PURPOSE
This section should cover what the sp ecification will control. Such as,
This specif ication establishes the engineering requirements for nam e process to be used by company name .
Personnel and machines used shall be able to meet or exceed this s pecification.
(b) 2.0 REFERENCES
The fo llowing publications are to be used to clarify this specification or be the ba sis for testing or equipment/personnel certification:
List other co mpany specifications, military specifications (MIL SPEC) or standards."
(c) 3.0 STANDARDS
3.1 Weld word vocabulary reference AWS A3.0-8 for definitions used in weld rela ted work.
3.2 Examples of acceptable and unacceptable weld should be shown in this section.
3.3 Method of certification and recertification of the welder. Weld specime ns and qualification and requalification test conditions.
3.4 Visual and radiographic inspection, metallographic examination and standards should be included in this section as applicable.
(d) 4.0 QUALIFICATION, CERTIFICATION, REQUALIFICATION, AND
RECERTIFICATION
The ability to weld or inspect to the requireme nt of this specification shows the person, process, and equipment are qualified. "Certified," means the weld er, welding procedure, and welding machine is qualified to make welds, and can make welds, to this specification.
4.1 Qualification requireme nt.
4.2 Equipment, machines, and process procedures should consist of such things as requir ed tooling, welding, schedule, pre-heat cycles, post-heat cycles, and required calibration of equipm ent.
(e) 5.0 MATERIALS
5.1 List welding rod and electrodes.
5.2 Gases.
5.3 Storage of rods and electrodes.
(f) 6.0 TECHNICAL
6.1 Inspection and manufacturing requirements.
6.2 Pre-heat and post-heat requirem ents if needed.
6.3 Heat treatment. This paragraph should cover any heat treatm ent required to restore all material in a weldment to a certain temper or tensile strength.
6.4 Detail gap - joint design information.
6.5 Describe weld repairs if applicable.
6.6 Cleaning, pre- and post-welding.
(g) 7.0 MANUFACTURING AND QUALITY CONTROL
7.1 Manufacturing requirements.
7.2 Quality control requirements.
m. Flutter.
(1) Regulation Reference. Section 23.629.
(2) Discussion. For general guidance on this section see AC 23.629-1A.
(3) Regulation Reference. Section 23.629 (b).
(4) Discussion. All airplanes certified to Title 14 CFR part 23, in any category, must perform flight flutter test(s) to show compliance in addition to any analytical methods.
(5) Regulation Reference. Section 23.629(d).
(6) Discussion. Airplanes that are the subject of this AC would typically meet the requirements of § 23.629(d)(1) through (d)(3). However, the applicant should review the criteria to ensure applicability. Based on the review of criteria, Engineering Report No. 45 (Simplified Flutter Prevention Criteria) could then be used to substantiate this portion of the regulations.
(7) Regulation Reference. Section 23.629(f)(2).
AC 23-15A, Change 1 3/15/05
(8) Discussion. For small low performance airplanes, designing the actuating structures to a factor of safety equaling four and providing redundant fastener safety as a means to minimize loss of single fastener joint integrity would be an acceptable method of showing compliance with this request.
n. Proof of Strength (Wings).
(1) Regulation Reference. Section 23.641.
(2) Discussion. Section 23.641 requires proof of strength of a stressed skin wing through tests or by combined structural analysis and load tests.
(a) Proof of strength of conventional aluminum or wood stressed skin wing structures primarily by analysis to limit and test to ultimate loads for the most critical bending and torsional wing load conditions is acceptable.
(b) In order to determine the most critical bending and torsional wing loads, one must complete a loads survey of the structure to determine which load case(s) produce the lowest safety margin against catastrophic failure of the wing. The actual mechanics of how to determine those specific load conditions requires qualified and experienced engineering personnel. The critical load conditions must be determined for the specific structural and airplane configuration, by detailed load and stress analysis. A specific explanation of this procedure that would be applicable for every airplane design doesn't exist.
(c) For conventional aluminum materials, the ultimate strength is typically less than one and a half times the yield strength. This means that as long as the article doesn't fail at the ultimate load, it will not yield at limit load. This rationale is for the worst-case scenario where the part fails in tension. For most structures however, failures occur due to instability first. The allowable ultimate load capability of a member in compression is lower than the tension capability.
This further reduces the difference between the ultimate and yield strength. Structural analysis should still be used to demonstrate that the yield strength is not exceeded at limit loads. If nonconventional aluminum is used, where this yield-to-ultimate strength relationship doesn't exist, then testing to ensure no yielding occurs at limit loads may be in order, at the ACO's discretion.
(d) In any event, part 23.307 is still app licable. Section 23.307 states in part that “Structural analysis may be used only if the structure conforms to those for which experience has shown this method to be reliable.” If in the ACO's judgment, the structure or analysis techniques used by the applicant, will not produce reliable analytical data, then testing may be in order.
(e) For wooden structures, there are no we ll-defined (published) yield strength values. When you observe the stress-strain curves for wood, it is evident that the relationship is not linear up to failure. The mechanism, that appears as yielding on the stress-strain curve, is actually micro cracks that develop within the matrix (lignin) between the fibers (cellulose). [3/15/05] These micro cracks have a negligible effect on the final ultimate strength [or—3/15/05] stiffness, of the material. Experience has shown that the ultimate strength test along with analysis is adequate to show compliance.
o. Landing Gear .
(1) Regulations Reference . Sections 23.723, 23.725, 23.726, and 23.727.
(2) Discussion .
(a) The designer selects the landing load factor, and the applicant is required to dem onstrate that the airplane will not exceed this factor when the aircraft is landing at the descent velocity specified by the regulations (reference § 23.473). For design purposes, this load factor may not be less than 2.67 and must not be exceeded by the certification drop tests specified in §§ 23.723 through 23.727.
(b) Alternatively, a conservative approach may be chosen by using a load factor of
4.2 g's to directly d etermine the static loads to be applied through design or static test to the landing gear. This load factor is considered conservative enough that it is unnecessary to verify it is not exceeded by an instrumented drop test. If this method (load factor of 4.2g's) is used, the only dynamic test required is the most critical drop test for reserve energy either in a fixture or by dropping the airframe, as described in § 23.727, without the need for instrumentation.
p. Brakes .
(1) Regulation Reference . Section 23.735.
(2) Discussion .
(a) A conservative rational analysis (§ 23 .735(a)(1)), or Technic al Standard Order (TSO) type tests (§ 23.735(a)(2)) and takeoff power test (§ 23.735(b)) are adequate for this class of airplane. (A rational analysis may include data such as service history, similarity to other approved brakes, etc., sufficient to increase the FAA's confidence level prior to installation/flight testing.)
(b) Additionally, taxi and landing stop test s to dem onstrate acceptable longitudinal and directional stability and control, and that no unacceptable vibrations, squeal, fade, grabbing, or chatter are present, are required in accordance with §§ 23.75, 23.143(a)(6), 23.231(a), 23.233(c),
23.493(c), 23.1301(d), and 23.1309(a)(1).
NOTE "Acceptable" means controllable by a pilot of any skill leve l.
q. Compartment Interiors/Powerplant Instruments .
(1) Regulations Reference . Sections 23.853 and 23.1337.
(2) Discussion .
(a) Section 23.853(e) does not prohibit direct reading oil pressure gauges, but it must be ". . . adeq uately shielded, isolated, or otherwise protected so that any breakage or failure of such an item would not create a hazard." Additionally, § 23.1337(a)(2)(i) and (ii) state that, "Each line . . . must have restricted orifices or other safety devices at the source of pressure to preven t the
30 escape of excessive fluid if the line fails; and be . . . located so that the escape of (such) fluid would not create a hazard."
(b) A direct oil pressure gauge line located in the cabin and f itted with an orifice of approximately 0.060-inch diameter located at the engine fitting limiting the flow of the oil into the cabin in the event of an oil line rupture inside the cabin is acceptable without a shrouded oil line vented overboard.
r. Fire Protection of Flight Controls, Engine Mounts, and Other Flight Structure.
(1) Regulation Reference . Section 23.865.
(2) Discussion . Two methods are available to validate that flight controls, engine mounts, and other flight structure can satisfy this requirement:
(a) Verify that the proposed components use a known fireproof material (example, steel or stainless steel). Or, as an alternative, a conformity inspection comparing the proposed assem bly to an existing Parts Manufacturer Approval (PMA) or product that is used in an existing type certificated aircraft can be accomplished.
(b) The applicant can validate components not previously approved by performing a fireproof test. Procedures for conducting such tests are contained in AC 20-135. A proposed test plan would need to be reviewed and approved b y the FAA prior to testing unless an existing TSO validation procedure is already published. The test would use a conformed control; a 2,000-degree Fahrenheit flame would be impinged onto the component and held in place for 15 minutes for fireproof compliance. Before removal of the flame at the termination of the test, loads should be applied to the component to show that it can still perform its intended function.
NOTE This portion of the regulations does not address engine controls. See part 23, § 23.1141(f) for requireme nts regarding the fire resistance testing for engine controls.
Also, the reader may refer to AC 23-17A, “Systems and Equipment Guide for Certification of Part 23 Airplanes” for more information.
s. Lightning Protection of Structure, Fuel System Lightning Protection, and S ystems.
(1) Regulations Reference . Sections 23.867, 23.954, and 23.1309(e).
(2) Discussion .
(a) Lightning testing is not required for those airplanes intended for operation under Visual Flight Rules (VFR) only. A general engineering overview of the airplane construction features to determine that any lightning induced hazards are minimized may be all that is required, if it can be determined that sufficient conductivity is available throughout the airplane and that the design employs features that have been found to minimize the hazard to the airplane and occupants.
Refer to FAA report number DOT/FAA/CT-89/22, “Aircraft Lightning
31 Protection Handbook” for best practices. The Type Certificate Data Sheet (TCDS) will contain this statem ent: "This aircraft is not approved for Instrument Flight Rules (IFR) operation under the provisions of § 91.205(d)."
(b) For those airplanes intended for opera tion under IFR a m ore detailed assessment will need to be made as to the vulnerability to lightning related hazards. Sections 23.867, 23.954, and 23.1309(e) of part 23 of the 14 CFR will need to be individually addressed. The depth of the verification should be commensurate with the degree of hazard. Since airplanes that employ conventional service proven construction and systems (i.e., all-aluminum airplanes with gyro flight instruments, magneto type engine ignition systems, mechanical fuel systems, etc.) have demonstrated over many millions of flight hours excellent inherent lightning protection qualities, similar designs may only need a qualitative engineering assessment that all hazards have been reasonably minimized. The Aircraft Lightning Protection Handbook, DOT/FAA/CT-89/22 may be used as a guide to make this assessment.
(c) Airplane designs that employ all composite construction, electronic flight instrum ent displays, electronic ignition systems, electronic fuel systems or electronic engine controls are generally more susceptible to lightning threats and, require further investigation. Therefore, airplanes that employ these designs are not within the scope of this AC. For electronic systems, see AC 20-53A, AC 20-136, and RTCA DO-160D for additional information. AC 23.1309-1C provides an acceptable means of identifying and assessing complex critical and essential systems.
(d) Airplanes using the foregoing means of compliance shall display the following lim itation placard: Not approved or eligible in Instrument Meteorological Conditions (IMC).
(e) See AC 23-17A “Systems and Equipmen t Guide f or Certification of Part 23 Airplanes” for more information.
t. Fuel Tank Tests .
(1) Regulation Reference . Section 23.965.
(2) Discussion . Certain requirements as defined in § 23.965(b) and (c) would be unduly burdensome in cases where certain small aluminum or nonmetallic fuel tanks incorporate side stiffeners or beads and internally attached baffles. The FAA tests described in § 23.965(a) satisfy the requirements if the tank has less than a 10-gallon capacity, or the tank interior has baffles (or equivalent support) at least every 15 inches in both directions.
u. Avionics Installation .
(1) Regulations Reference . Sections 23.1301, 23.1431, 23.1309(a), and 23.1311.
(2) Discussion .
(a) Section 23.1301 requires that all installed equipment perform its intended functions. For comm unication and navigation equipment required for IFR operations, an acceptable means of performance evaluation of these systems is provided in AC 23-8B, chapter 5.
(b) For non-required navigation and communication equipment that could be used for flight purpo ses and which have not been previously approved, an acceptable means of performance evaluation of these systems is provided in AC 23-8B, chapter 5, and AC 23.1309-1C. For optional equipment that has no functions that can be utilized by the flight crew for the purpose of flight (i.e., stereo receivers, television sets, tape players, etc.), the intended function is considered to be the lack of any hazardous failure modes and the non-interference with other required equipment installed in the airplane. Evaluation of these systems should address only those failure modes or performance qualities that would directly result in hazard (fire, smoke, explosion, etc.) or indirectly affect safety by interfering with the operation of required equipment. Typically, FAA flight test pilot observation is adequate to determine any affects of interference. Non-flight related functions do not need to be evaluated. An acceptable method of evaluating adverse effects and minimizing hazards in accordance with § 23.1309(a) is provided in AC 23.1309-1C.
(c) The requirements of § 23.1431 are self-e xplanatory and parallel the requirem ents of § 23.1309(a).
(d) The requirements of § 23.1311 pertain to the certification of electronic display instrum ent system installations. An acceptable means of compliance with the specific requirements of § 23.1311 are provided by AC 23.1311-1A.
(e) For communication and navigation equipment with previous installation approvals, an acceptable m eans of performance evaluation of these systems is outlined below (the intent is to verify the installation, not the ability of the already proven system):
1. Very High Frequency (VHF ) Communication Transceivers. For VFR, establish satisfactory communications with the tower while on the airport ramp and in flight at 20+/-5 Nautical Mile (NM) and the higher of 2,000 feet Above Ground Level (AGL) or Minim um Obstruction Clearance Altitude (MOCA). The flight path relative to the tower includes toward, away, 90 degrees right and 90 degrees left while in level flight at cruise power.
2. VHF Navigation Receivers . For VFR, tune to a Visual Omni Test (VOT), or use a Visual Omni Range (VOR) checkpoint (+/-4 degrees tolerance), and fly to a VOR airborne checkpoint and check for accuracy within IFR tolerances (+/-6 degrees). The audio signal must be clearly audible.
3. VHF Area Navigation (RNAV) Systems . VFR only: establish waypoint over known position and confirm accuracy, per the manufacturer's instructions. IFR approvals may be done in accordance with AC 20-121A, AC 20-130A, or applicable Global Positioning System (GPS) certification guidance.
4. Automatic Direction Finde r (ADF) Navigation Systems. For VFR, tune to known station; check bearing indication against known position, on the ground and at 2,000 feet AGL, or MOCA, (whichever is higher) at 20+/-5 NM, for two positions. Errors must not exceed +/- 5 degrees, and the aural signal must be clearly audible.
5. Transponders, Mode A . For VFR, ask approach control or center to confirm operation, in the traffic pattern and at 2,000 feet AGL or MOCA (whichever is higher), at 20 NM.
6. Transponders, Mode C . For VFR, same as (v), also requesting altitude check, starting at 2,000 feet AGL, or MOCA (whichever is greater), and continuing every 2,500 feet up to 90 percent of service ceiling; starting the climb at 10 NM and ending at 80 NM from the station.
7. Long Range Navigation Communication (LORAN-C) Systems . Use VFR only criteria of AC 20-121A.
8. Electro Magnetic Compatibility . With all systems exercised in flight, verify by observation that no adverse effects are present in the installed equipment.
v. Equipment Systems and Installation .
(1) Regulation Reference . Section 23.1309.
(2) Discussion . For those airplanes with equipment installations where a single failure would not cause loss of safe flight capability, or if not limited to VFR operation, a failure would not result in a significant reduction in the ability of the crew to cope with adverse operating conditions, § 23.1309(a) is applicable. An example would be loss of the primary attitude indicator during an IFR flight where the pilot can maintain control of the airplane by other means such as use of a secondary attitude indicator or use of partial-panel piloting techniques. In this instance, further evaluation would not be needed other than the requirements of § 23.1309(a), which addresses adverse effects on other equipment, the minimizing of hazards on single engine airplanes, and the prevention of hazards on multiengine airplanes. The methods of compliance outlined in AC
23.1309-1C, figure 1 and paragraph 7, are acceptable for evaluating these systems.
(a) For those airplanes with equipment installations whose fa ilure conditions are catastrophic, the requirem ents of § 23.1309(b) are also applicable. The methods of compliance outlined in AC 23.1309-1C, paragraphs 9 and 10 are acceptable for evaluation of these systems.
(b) The general considerations of § 23.1309(c) and (f) are self-explanatory and are applic able to all airplanes being evaluated. Paragraph (d) is applicable only to commuter category airplanes (this intent was inadvertently omitted with the adoption of amendment 23-41). Paragraph
(e) is applicable to all installations with critical or essential functions that are also susceptible to lightning threats and radio frequency energy threats (other than High Intensity Radiated Fields (HIRF). This is discussed in paragraph "5s" of this AC and in AC 23.1309-1C, paragraph 11.
(c) Those systems employing software in their design will need further evaluation.
AC 23.1309-1C, paragraph 12 discus ses this. AC 20-115B, and RTCA/DO-178B, is an acceptable means of assessing these systems.
w. Airplane Flight Manual .
(1) Regulations Reference . Sections 23.1581, 23.1585, and 23.1587.
(2) Discussion . For small airplanes, compliance is met by computing performance at two temperatures--standard day, and standard day +30 degrees Centigrade, and at least three altitudes for takeoff and landing distance and climb data expanded to a minimum of 10,000 feet altitude. A
presentation (the use of tables/charts rather than graphs) similar to that found in figure 13 is acceptable.
TAKE-OFF DISTANCE-FLAPS RETRACTED-HARD SURFACE RUNWAY @ 1600 LBS WT. & 68 KNOT CLIMB SPEED Sea Level (59F) 2500 FT (50F) 5000 FT (40F) 7500 FT (32F) Wind DISTANCE 50 FT ALT DISTANCE 50 FT ALT DISTANCE 1115 1985 1360 2440 10 500 1035 800 1250 780 1530 970 1875 20 305 730 395 890 505 1090 840 1375 Notes 1lIncrease the distances 10% for each 35F increase in temperature above standard for the particular altitude 2 For operation on dry, grass runway, increase distances (both "DISTANCE" and "Total to clear 50FT ALT".) by 7% of the "50FT ALT." figure.
MAXIMUM RATE-OF-CLIMB DATA @ 1600 LBS SEA LEVEL (69F) 5000 FT (41F) 10,000 FT (23F) JAS R.O.C. Fuel Used R.O.C. Fuel Used JAS R.O.C. Fuel Used Gal. S.L. GAL S.L. GAL.
74 670 0.6 71 440 1.6 67 220 3 Notes 1 Flaps retracted, full throttle, mixture leaned to smooth operation above 5000 FT.
2 Fuel used includes warm-up and take-off allowances 3 For hot weather, decrease rate of climb 15FT/min for each 10F above standard day temperature for particular altitude LANDING DISTANCE-FLAPS 40 DEGREES, POWER OFF HARD SURFACE RUNWAY--ZERO WIND @ 1600 LBS. & 60 KNOTS SEA LEVEL (59F) 5000 FT (50F) 5000 FT (41F) 7500 FT (32F) DISTANCE 50FT ALT DISTANCE 50FT ALT. DISTANCE 50FT ALT. DISTANCE 50FT ALT 445 1075 470 1135 495 1195 520 1255 Notes 1 Decrease the distances shown by 10% for each 4 knots increase in headwind 2 Increase the distance by 10% for each 60F temperature increase above standard.
3 For operation on a dry, grassy runway, increase distances ("Both "DISTANCE" and Total to clear 5OFT ALT.") by 20% of the " 50FT ALT." figure Figure 13 - PERFORMANCE CONTENT AND FORMAT 34