(bb) Maximum takeoff weight is limited by structural integrity or airplane performance.
(6) The Airplane Flight Manual (AFM) should clearly present these limitations to the pilot.
(7) Display maximum ramp weight limitations in at least two places—the Type Certificate Data Sheet and the AFM.
(8) Obtain the correct fuel capacity and fuel weight to show compliance for design landing weight (reference § 23.473(b)(2)) by using the following:
(a) The entire airplane fuel capacity (including unusable and residual fuel), with 1 The maximum appropriate fuel densities shown in the Note found in the Powerplant Guide for the Certification of Part 23 Airplanes (AC 23-16),
23.955 Fuel flow, (c) Pump Feed Systems, paragraph (3).
2 For avgas, use 6.0 pounds per gallon.
113. Why did a prior amendment level refer to part 25 regulations?
Before Amendment 23-7, § 23.473(c) referred to the requirements of § 25.1001 for fuel jettison requirements.
Warning: The design landing weight of a part 23 airplane may be less than that allowed by § 23.473 when a fuel jettisoning system is installed and the one engine inoperative rate-of-climb requirements of § 23.67(a) are met.
The other requirements related to this subject are so different in parts 23 and 25 that the jettisoning requirements of current part 25 are not compatible with part
23. These differences include structures and loads, aircraft performance, and accounting for temperature and altitude effects.
Therefore, the FAA did not intend the jettison requirements of part 25 (Amendment 25-18) to be applied to part 23. The preamble of Amendment 23-7 states that amended § 25.1001 does not now reflect the appropriate requirements for part 23. Amendment 25-18 was intende d to cater to the needs of airline transport airplanes and to preclude the need for additional exemptions from the pre-amendment jettisoning requirement.
114. Is there any policy available on paragraph (d), (e), (f) or (g) of this section as of January 1, 2007? No.
115. Where can I find more information about an increase in maximum weight, maximum landing weight, or maximum zero fuel weight? More information may be found in 23.307, Proof of structure.
116. What weight should be used in showing compliance with §§ 23.485, 23.493, and 23.499 (side load conditions, braked roll conditions, and supplementary conditions for nose wheels)? The design landing weight may be used in showing compliance to these regulations.
Other ground load conditions, which address ground handling or taxiing conditions, should be substantiated to the design maximum weight.
117. Can I establish separate land and water weight limits for amphibian airplanes? Yes.
Separate weight limits are acceptable for amphibians for operation on land and on water because separate certification criteria exist within the regulations.
118. What are the appropriate ground load conditions for an amphibious airplane design?
a. For an amphibious airplane design, the following ground load conditions and assumptions are appropriate (see § 23.473, paragraphs (e), (f), and (g)) when the design landing weight is less than the maximum weight (see § 23.473 (b)):
(1) § 23.473(d) - Determine the landing descent velocity from 14/ W ⎞ ⎠⎟
(2) § 23.473(e) - Assume a wing lift not exceeding two-thirds of the airplane weight exists throughout the landing impact; and
(3) § 23.473(f) - Energy absorption tests.
119. Can I use a landing weight less than the design maximum weight in § 23.473(g)? No.
That is inappropriate since the airplane inertial load factor may not be less than 2.67.
Correspondingly, the ground reaction load factor may not be less than 2.0 at design maximum weight.
120. How much can the gross weight be increased by analysis of prior drop tests without actually conducting a drop test at the increased weight?
a. Any answer should consider all the factors, such as remaining shock-strut travel, metering pin design, energy absorption characteristics (area under the accelerometer time-history trace), etc., and how those factors change at the increased gross weight configuration. The need to conduct or ignore drop tests should be reviewed cautiously.
● Policy: A decision about whether the maximum weight increase is “small” or “substantial” does not affect the application of guidance in this AC.
⎛⎜⎝ V
44.
;
= S
23.477 Landing gear arrangement (Original)
121. Is there any policy available on this section as of January 1, 2007? No.
23.479 Level landing conditions (Amendment 23-45)
122. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
123. What is the background of paragraph (b) of this section?
a. The drag component for landing gear loads may not be less than 25 percent of the design load factor multiplied by the gross weight of the airplane. This equation is observed in Appendix C of part 23 under main wheel loads. This does not mean that a separate drop of the main gear, at maximum gross weight, is required to obtain the load factor used in making this calculation.
b. Two different incline plane angles are given in the Civil Air Regulations (CAR) and Title 14 of the Code of Federal Regulations (14 CFR).
c. Approvals have been granted using CAR 3, before May 3, 1962, which defines the inclined plane angle to be ARC tan K for the level landing case with the nose wheel just clear of the ground. In CAR 3 (Amendment 3-7), dated May 3, 1962, the regulations show the inclined plane angle to equal ARC tan [nk/(n-L)] (see CAR 3.245(b)(2). See Figure 3-12(b), and § 23.479(a)(2)(ii), Appendix C of part 23). Manu facturers of amphibious floats for aircraft certificated under part 23 have used inclined plane angles as ARC tan K. There are no unfavorable service history records of landing gear failures for part 23 airplanes that were substantiated and approved for the main landing gear drop test using the old CAR 3 regulations.
• Policy: CAR 3 landing gear drop test data substantiated to requirements dated before May 3, 1962, are not acceptable for aircraft certificated to CAR 3 or part 23 on or after the 1962 date.
124. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
125. Is there any policy available on paragraph (d) of this section as of January 1, 2007?
No.
23.481 Tail down landing conditions (Original)
126. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
127. What are “spin-up” and “spring-back” loads?
a. When a landing airplane wheel touches the ground, a near instantaneous wheel spinup occurs (since the wheel tangential velocity should quickly match that of the runway). Due to inertial properties, this phenomenon induces a drag load upon the landing gear. The drag force energy is stored in the landing gear as potential energy that causes the gear to spring-back (a negative drag force). The drag forces of spin-up and spring-back may reach maximum values at different times than when the vertical load on the landing gear is achieved. It would be unusual for both load maximums (drag and vertical) to occur simultaneously.
128. Should there be a drag load (spin-up), combined with the vertical load, for paragraph
(b), tail down landing conditions?
a. A primary concern about the last phrase of paragraph (b) is that it can be interpreted at least two ways. The two interpretations are as follows:
(1) Since the wheel is assumed up to speed, the drag load caused by wheel spin-up is zero.
(2) Maximum wheel spin-up and spring-back occur before the landing gear maximum vertical load is attained; therefore, the drag load due to spin-up or spring-back combines with earlier lower-magnitude vertical loads but does not combine with the maximum vertical load.
b. The second interpretation of the regulation is correct. The different interpretations of tail-down landing requirements come from the Basic Landing Conditions table shown in Appendix C of part 23. The ta ble does not include a load, Dr, which accounts for spin-up and spring-back loads. However, Appendix D provides Dr loads for the same landing conditions shown in Appendix C.
129. How are the landing gear loads typically determined and tested?
a. Airplane landing gear designers often estimate these loads analytically and test for these loads by dropping the airplane or the landing gear units. The drag loads are sometimes approximated using inclined planes (wedge blocks) and, at other times, they are created by reverse spinning the wheel and tire before the drop impact.
b. Incline planes are often suitable for small airplanes where the touchdown velocity is relatively small and the wheel and tire diameters are correspondingly small. Incline planes, which are used to induce the estimated drag load, may restrict proper development of the springback (negative drag) load—and should be viewed accordingly. For small airplane landing gear designs, incline planes may be an adequate method to use to show compliance with part 23.
c. Reverse wheel spin-up, to simulate the drag load caused by wheel spin-up, is frequently used by landing gear designers for larger, faster, airplane designs. Higher touchdown speeds and larger diameter tires cause disproportionate increases in the wheel and tire inertial properties; these create larger magnitude spin-up and spring-back loads.
• Policy: Reverse wheel spin-up and in cline planes are both acceptable methods for imposing the drag inputs into a drop test when they are properly applied. Also see § 23.725(c).
23.483 One-wheel landing conditions (Original)
130. What wing lift should I use for this condition? Use wing lift consistent with that used for the other landing impact conditions.
23.485 Side load conditions (Amendment 23-45)
131. Is there any policy available on this section as of January 1, 2007? No.
23.493 Braked roll conditions (Original)
132. Is there any policy available on this section as of January 1, 2007? No.
23.497 Supplementary conditions for tail wheels (Amendment 23-48)
133. Is there any policy available on this section as of January 1, 2007? No.
23.499 Supplementary conditions for nose wheels (Amendment 23-48)
134. Is there any policy available on this section as of January 1, 2007? No.
23.505 Supplementary conditions for skiplanes (Amendment 23-7)
135. What is the typical method for determining the load factor for a ski installation?
a. A ski installation should use a load factor determined by either of the following two methods:
(1) Perform drop tests, with skis installed, on a surface simulating frozen hardpacked snow or ice; or
(2) Use a conservative formula (see SPECIFICATION—Aircraft skis, National Aircraft Standards Committee, NAS 808, paragraph 5.1(a)).
b. Ski installation factors should include consideration for fittings, tubes, axles, nuts, bolts, etc., which attach the skis to the fuselage. Ski-gear loads normally run about 115 percent to 125 percent of wheel-gear loads. Also see 23.737, Skis.
23.507 Jacking loads (Amendment 23-14)
136. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
137. How do I meet the intent of paragraph (b) of this rule? The intent is accomplished when structure affected by jacking loads is designed to withstand the inertial load factors in part 23, § 23.507(a)(2) and (c). Section 23.507( b), in essence, is redundant with § 23.471 General (Ground Loads).
138. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
23.509 Towing loads (Amendment 23-14)
139. Is there any policy available on paragraph (a), (c) or (d) of this section as of January 1, 2007? No.
140. What is an auxiliary gear? Auxiliary gear means a landing gear unit that is not part of the main landing gear.
23.511 Ground load; unsymmetrical loads on multiplewheel units (Amendment 23-7)
141. Is there any policy available on this section as of January 1, 2007? No.
WATER LOADS
23.521 Water load conditions (Amendment 23-48)
142. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
143. Is there any policy available on paragraph (b) of this section as of January 1, 2007?
No. See 23.603, Materials and workmanship, for information that pertains to floats.
23.523 Design weights and center of gravity positions (Amendment 23-45)
144. Is there any policy available on this section as of January 1, 2007? No.
23.525 Application of loads (Amendment 23-45)
145. Is there any policy available on this section as of January 1, 2007? No.
23.527 Hull and main float load factors (Amendment 23-45)
146. Is there any policy available on paragraph (a) or (b) of this section as of January 1, 2007? No.
147. Does the term “seaplane structure,” as used in paragraph (c), apply to the engine mounts? Yes. Therefore the factor K 1, used in the calculation of the water reaction load factor nw, may be reduced at the bow and stern to 0.8 of the value shown in figure 2 of appendix I in part 23.
23.529 Hull and main float landing conditions (Amendment 23-45)
148. Is there any policy available on this section as of January 1, 2007? No.
23.531 Hull and main float takeoff condition (Amendment 23-45)
149. Is there any policy available on this section as of January 1, 2007? No.
23.533 Hull and main float bottom pressures (Amendment 23-45)
150. Is there any policy available on this section as of January 1, 2007? No.
23.535 Auxiliary float loads (Amendment 23-45)
151. Is there any policy available on this section as of January 1, 2007? No.
23.537 Seawing loads (Amendment 23-45)
152. Is there any policy available on this section as of January 1, 2007? No.
EMERGENCY LANDING CONDITIONS
23.561 General (Amendment 23-48)
153. Is there any policy available on paragraph (a) of this section as of January 1, 2007?
No.
154. What are the historical requirements of this section in reference to Cargo Restraints?
a. Guidance information about ultimate inertial strength requirements for cargo restraint devices in part 23 airplane designs originally centered around part 135 air taxi operators who carried mail sacks in an empty cabin after passenger seats were removed. The guidance is from around 1968.
b. There is an inconsistency between Civil Air Regulations (CAR) 3.386(d) and § 23.561(e), in recodified part 23, dated February 1, 1965. The inconsistency concerns protecting occupants from mass items that might cause injury if they come loose in a minor crash landing (up to 9g’s). Another inconsistency exists between CAR 3.392 and § 23.787(c) when considering occupant protection. This inconsistency concerns the cargo compartment contents ultimate forward acceleration of 4.5g’s. Another inconsistency exists between CAR 3.392 and § 23.787(c). Section 23.787(c) sugges ts that a designer should also consider the maximum flight and ground-load factors for load conditions.
c. As originally viewed, CAR 3.392 applied to airplane configurations that contained a forward crew compartment, a center passenger compartment, and an aft bulkhead, which separated a small cargo compartment from the passenger area. In this configuration, 4.5g restraint was considered adequate since the National Aeronautics and Space Administration (NASA) data showed that, in a typical crash, the g-forces became lower as distance increased aft from the airplane nose. Thus, what would be adequate cargo restraint in the aft fuselage would probably be inadequate near the cockpit. When CAR 3.392 was adopted, the Civil Aviation Authority did not envision all-cargo CAR Part 3 aircraft.
d. For § 23.561(b) and (e), the restraining devices should meet the 9g requirement.
155. What are the historical requirements of this section in reference to Cargo Compartment Design?
a. Regulatory history about cargo compartment design practices and minimum airworthiness standards guidance is from around 1968.
b. CAR 3.392 requires a cargo restraint of 4.5g forward inertial load factor when structure separates the contents in a cargo compartment from occupants forward of the compartment. Section 23.787 requires a cargo restraint of 9.0g forward inertial load factor when structure separates the contents in a cargo compartment from occupants forward of the compartment. At Amendment 23-36, the FAA increased the mass item retention to 18.0g for occupant protection when the mass items are located in the cabin with the occupant (i.e., not located in a separated cargo compartment).
c. The emergency provisions protection, the intent of CAR 3.386, is as follows: Each acceleration specified in CAR 3.386 should be considered to act independently. If the occupants’ heads could strike sharp edges of objects within the passenger cabin under combinations of load factors less than those given in CAR 3.386(a), then the designer should use 55
the general requirement of the first paragraph of CAR 3.386 with the guidelines of CAM
3.386-1.
156. What are the historical requirements of this section in reference to Cabin Safety?
a. Airplane designers (and modifiers) and FAA Aviation Safety Engineers should pay attention to the need for increased emphasis in the design of cabin safety provisions in small airplanes. Observe the following guidelines: Strive for the highest level of occupant crash protection feasible within the state-of-the-art technology for the general emergency landing conditions and the occupant protection provisions given in §§ 23.561, 23.562 and 23.785. Do this early and frequently in the Type Certification Process.
b. Cabin safety emphasis is intended to influence an individual designer’s choices early in the conceptual phases, when safety objectives can be achieved with little or no burden on the designer and the manufacturer. The level of occupant crash protection is determined by interrelated cabin features including, but not limited to, the following:
(1) Seating configuration (considering occupant flailing characteristics);
(2) Occupant restraint devices, supports, attachments, and installations;
(3) Energy absorbing padding (thoughtfully located); and
(4) Potentially hazardous hard points.
c. To clarify confusion about static side load factors: Mass items have a 4.5g static side load factor requirement, whereas occupants have only a 1.5g condition.
d. The occupant sideward static load factor requirement of 1.5g was recodified into § 23.561(b)(2)(iii) from the Civil Air Regulations, Part 3. Twenty-three years later, part 23, Amendment 23-36, put the 4.5g mass item requirement into the seat and restraint systems dynamic test requirements. The General Aviation Safety Panel (GASP) studied and recommended these actions.
e. GASP I, as the first group was known, recognized that 26g times the SIN 10° equals
4.5g, which is the sideward dynamic emergency landing condition for an airplane impact associated with a yaw. They further recognized that it would be much more economical to conduct static tests, or analyses, than dynamic tests for mass items installed on the airplane.
Consequently, GASP I recommended the static load factor now contained in § 23.561(b)(3).
157. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
No.
158. What is the background of protection of occupants in an airplane for a sliding bubble canopy and with no turnover structure? Until Amendment 23-36, effective September 14, 1988, the turnover requirement in § 23.561(d) was essentially the same as in CAR 3.386(c), which first appeared in CAR 3, as amended in November 1949.
159. What are the requirements of this section for airplane turnover?
a. Regardless of the type of landing gear installed, the inverted attitude is probable;
therefore, the emergency exit requirements of § 23.807(a) should be demonstrated unless escape means are obvious.
b. Figure 8 presents an overall relational view of turnover protection airworthiness standards.
FIGURE 8
RELATIONAL VIEW OF TURNOVER PROTECTION
c. To meet the static emergency landing conditions requirements (see § 23.561(d)), the strength of turnover structure may be shown by analysis. However, conduct tests if an analysis is questionable (see § 23.601).
160. Is there any policy available for this section on a Jettisonable Canopy?
a. The airworthiness standard for § 23.807(a), Emergency exits, requires that emergency exits be located to allow escape in any probable crash attitude. Compliance with this requirement should be demonstrated with a rollover structure installed.
b. Section 23.807(b)(4), the emergency exits regulation, requires each emergency exit to have reasonable provisions against jamming by fuselage deformation. Compliance with this requirement should be demonstrated with the airplane resting inverted after accounting for any structural collapse.
c. In an acrobatic category airplane, the occupants should be able to bail out quickly, with parachutes, at any speed between VSO and VD (see § 23.807(b)(5)). Further, § 23.807(c) requires that the proper functioning of each emergency exit be shown by tests, which are usually demonstrated on the ground rather than in flight.
d. Forward sliding, jettisoning, and hinged canopy designs were not originally envisioned by CAR 3 or part 23. Occupant protection and escape from an airplane damaged in a turnover, and in-flight emergency escape provisions, should be addressed in any certification project, since adequate emergency exit airworthiness standards exist in these regulations.
Special conditions may be required for a jettisonable canopy to address continued safe flight, inadvertent canopy opening hazards, and in-flight canopy jettison-safe trajectory. Other possible methods of showing compliance to the airworthiness standards include wind tunnel tests, sled tests, or other ground tests that simulate flight.
e. A jettisonable canopy may not jam when the airplane is resting inverted.
f. For the bail-out requirement of § 23.807(b)(5) for an acrobatic category airplane:
(1) If the canopy is not jettisonable, show that the occupants can safely exit the airplane between VSO and VD.
(2) If the canopy is jettisonable, show that the canopy trajectory will not injure the occupants while separating from the airplane between VSO and VD. Also demonstrate that the airplane can continue safe flight and landing without the canopy. Alternatively, inadvertent canopy jettison should be improbable.
161. Is there any policy available for this section on Emergency Exit requirements in an Airplane Turnover Condition?
a. The inverted attitude is a probable crash attitude for small airplanes. The occupant emergency exit requirements of § 23.807(a) should be shown. If escape from the inverted attitude airplane is not obvious, or is questionable, compliance should be by demonstration.
b. It is not acceptable to rely on an emergency procedure that requires canopy jettison immediately before an impact accident (except for an in-flight canopy jettison above a safe parachute altitude required in § 23.807(b)(5)). If the canopy is made jettisonable, to comply with § 23.807(b)(4), avoid jams with fuselage deformation when the airplane is resting inverted. If there is any doubt, the applicant should demonstrate by tests.
162. Is there any policy available on paragraph (e) of this section as of January 1, 2007?
No.
163. Do internal cabin doors have to remain operational after an emergency landing? Do not allow an internal cabin door to jam during an emergency landing and block the flight crew’s escape path. See the Systems and Equipment Guide for Certification of Part 23 Airplanes, AC 23-17B, 23.807 Emergency Exits, for further guidance.
164. What minimum occupant weight should I use? Use, at least, the following minimum occupant weights when showing compliance with the emergency landing conditions static strength airworthiness standards of § 23.561:
a. Design each seat and its supporting structure for an occupant weight of at least 170 pounds, for normal and commuter category airplanes. Use a 190-pound occupant weight, which includes a parachute, for utility and acrobatic category airplanes. (Reference § 23.25(a)(2).)
b. Also, design each seat and restraint system for at least a 215-pound occupant weight when considering maximum flight and ground-load conditions of the airplane-operating envelope.
NOTE: A 1.33 factor should be applied to all load s that affect the strength of fittings and attachment of the following:
(1) Each seat to the structure, and
(2) Each safety belt and shoulder harness to the seat or structure.