41 Guidelines for performing a design safety assessment by application of § 23.1309(b), as adopted by Amendment 23-41, are given in AC 23.1309-lE. This AC also provides guidance on design safety assessments, environmental and atmospheric conditions, and software assessment.
23.703 Takeoff warning system
There are no corresponding rule or airworthiness criteria in CAR 3 or the Airship Design Criteria.
Amendment 23-49 and Subsequent
This amendment adopted a proposed revision in NPRM 94-21 that stated: “This proposed new section would require a takeoff warning system on some commuter category airplanes.
The requirement would be applicable if the flight evaluation showed that an unsafe takeoff condition would result if lift devices or longitudinal trim devices are set to any position outside the approved takeoff range. If the evaluation shows that no unsafe condition would result at any setting of these devices, a takeoff warning system would not be required. For those airplanes on which a warning system must be installed, the proposal would provide requirements for the installation of the system.”
Amendment 23-62 and Subsequent
In Docket No. FAA-2009-0738, the Discussion of the Regulatory Amendments stated: FAA revised the language in the introductory text and § 23.703(b) to add takeoff warning system requirements to all airplanes over 6,000 pounds and all jet airplanes. The definition of an unsafe condition is the inability to rotate or the inability to prevent an immediate stall after rotation. High temporary control forces that can be quickly trimmed out would not necessarily be considered unsafe.
This amendment has three effects:
1. Maintains the requirement for a takeoff warning only if no unsafe condition results from any setting of lift and longitudinal trim devices outside the approved takeoff range.
2. Changes the applicability from only commuter category airplanes to all jets and any reciprocating or turbopropeller engine airplane over 6,000 pounds,
3. Defines an unsafe takeoff configuration as the inability to rotate or the inability to prevent an immediate stall after rotation.
The Final Rule added the prior § 23.703(b), which was deleted by mistake in the NPRM.
Section 23.703 is modified to correct the error that deleted § 23.703(b).
43 Section 2. Landing Gear
23.721 General
The Small Airplane Directorate has no criteria or policy for taxi over rough surfaces for small airplane landing gear design. Manufacturers are free to develop and substantiate their own criteria.
There are no corresponding rule or airworthiness criteria in CAR 3 or the Airship Design Criteria.
23.723 Shock absorption tests
The corresponding rules in CAR 3 are CAR 3.351 and 3.352.
The corresponding airworthiness criteria is section 4.24, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue
This regulation requires shock absorption tests be performed for certification.
Amendment 23-23 and Subsequent
This amendment allows an analysis rather than a shock absorption test, but to do so the applicant should have a landing gear system with identical (similar is not acceptable) energy absorption characteristics. The energy absorption characteristics of the landing gear system (for example, structure, wheel tire, and shock absorber) should be included in determining the response of the landing gear system. The tests should cover a range of energy absorption characteristics and weights over which the analysis is shown to be valid. If these conditions are not met, drop tests will be required to substantiate maximum takeoff and landing weight increases. It is acceptable to modify individual gear drop test data by adapting the results to the complete aircraft analytically, accounting for the aircraft flexibility.
23.725 Limit drop tests
The corresponding rules in CAR 3 are CAR 3.353 and 3.354.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
Original Issue
This rule gives requirements for limit load drop tests if the applicant uses free drop tests to meet the requirements of § 23.723(a). The applicant should make ten drops from limit height for each basic design condition. The applicant should make one drop from the height (maximum is 2.25 times the limit drop height) needed to develop 1.5 times the limit load using the limit drop weight. It is acceptable to modify individual gear drop test data by adapting the results to the complete aircraft analytically, accounting for the aircraft flexibility.
Amendment 23-7 and Subsequent
This amendment requires the limit inertial load factor be determined in a rational and conservative manner during the drop test using a landing gear unit attitude and applied drag loads that represent the landing conditions. It is acceptable to modify individual gear drop test data by adapting the results to the complete aircraft analytically, accounting for the aircraft flexibility.
23.726 Ground load dynamic tests
No policy available as of December 31, 2007.
There are no corresponding rule or airworthiness criteria in CAR 3 or the Airship Design Criteria.
23.727 Reserve energy absorption drop test
The corresponding rule in CAR 3 is CAR 3.355.
There is no corresponding airworthiness criteria in the Airship Design Criteria.
Amendment 23-7 and Subsequent
Section 23.727(b) requires the effect of wing lift be provided for in reserve energy drop tests.
You should also use the applicable drag loads, as specified in § 23.725(c).
23.729 Landing gear extension and retraction system
The corresponding rules in CAR 3 are CAR 3.356, 3.357, 3.358 and 3.359.
The corresponding airworthiness criteria is section 4.25, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue
14 CFR, part 23, does not define landplanes, seaplanes and amphibians. These terms passed unchanged from CARs 3 and 4. As FAA uses them, landplanes can only land on the ground, seaplanes (both boat and float types) can only land on water, and amphibians can land on both water and on the ground.
Therefore, where a rule such as § 23.729(c) states "landplanes" it does not apply to seaplanes or amphibians. When the rule states "airplanes" such as § 23.729(a) it applies to any aircraft that incorporates that equipment. Thus, § 23.729(a) can apply to landplanes and amphibians, but not seaplanes since they don't have retractable land gear.
Amendment 23-7 and Subsequent
A warning device with no manual shutoff is required when the flaps are “to or beyond” the approach flap setting if the landing gear is not down and locked. The “to or beyond” phrase in using a normal landing procedure is intended to provide for differences in design, as follows:
a. For airplanes whose normal procedures only prescribe landings with flaps extended past the approach setting, only the “beyond” aspect of this rule is appropriate. Operating information for these airplanes should suggest that landings with approach flaps, or less, are not normal and will not activate the flap/landing gear aural warning.
b. For airplanes whose normal procedures incl ude landings with a flap setting at the approach setting, the “to and beyond” aspect of this rule is appropriate. Designers may choose to include additional logic in the flap/landing gear warning system, such as airspeed, thrust/throttle position. This logic may minimize nuisance warnings and may provide the equivalent safety intended by the rule.
Because part 23 is not specific about flap positions used, we cannot specify the flap position that actuates the warning device. This rule provides a basis for the FAA and the applicant to agree on the set point for the warning device.
Although not defined in part 23, most airplanes do have a “normal landing procedure” and an “approach flap position.” The flap position will vary among models, but it is this position that should be used to show compliance. For Amendment 23-21, NPRM 75-25, changed this section. The NPRM explanation stated as follows: “The present rule requires that a manual shutoff for the aural landing gear warning device be installed so that reopening the throttle
49 will reset the device. However, when an engine has been shut down in flight, its throttle may not be reopened before landing. The proposal would require the aural warning to be activated when any throttle is subsequently retarded to or beyond the position for a normal landing approach, thus requiring the warning intended by § 23.729(e)(2) regardless of the position of any other throttle and the prior deactivation.”
Amendment 23-45 adopted NPRM 90-18, which changed this section again. The NPRM states as follows: “This proposal revises § 23.729(f)(1) and (2) by changing the power and flap settings necessary to activate the device that warns the pilot that the landing gear is not fully extended and locked. The power setting necessary to activate the warning device is changed from when one or more "throttles are closed" to when one or more "throttle are closed beyond the power settings normally used for landing approach." The flap setting necessary to activate the warning device is changed from "flaps are extended to or beyond the approach flap position" to "flaps are extended beyond the approach flap position."
This information is applicable to the structural substantiation to the loads resulting only from all yawing conditions for the landing gear doors and retraction mechanism of small airplanes for part 23, § 23.729(a)(2).
Section 23.729(a)(2) requires the landing gear doors and retraction mechanism to be substantiated for the loads resulting from all yawing conditions. Attempts have been made to meet these requirements by flight testing to dive speed with some yaw or by flight testing at full yaw at a lower speed. These procedures normally do not result in a test that substantiates a 1.5 factor of safety. If substantiation by flight testing is desired, the landing gear doors and retraction mechanism should be subjected to 1.5 times the limit "q" loading. The limit “q” loading is the “q” at VLE or VLO whichever is greater.
The higher of the above speeds at which Vq is to be computed is designated as VLG.
Acceptable Means of Compliance
One method, but not the only method, for showing compliance with the structural requirements of § 23.729(a) (2) for the loads resulting from all yawing conditions for the landing gear doors and retraction mechanism is as follows:
a. Substantiation may be accomplished by flight testing at a speed of Vq and the yaw angle determined in paragraph a (3) below, unless this will exceed the structural limitation as determined by analysis, static test, or a combination of both, where:
(1) V q = square root of (VLG squared times 1.5).
(2) V LG = The greater of VLO or VLE.
(3) For the yawed condition, the limit “q” load will be at V LG with the airplane at the yaw angle determined by § 23.441. This angle need not exceed 15 degrees.
Substantiation should be to 1.5 “q”.
(4) If V q is equal to or less than VA, substantiation by flight test may be accomplished.
(5) If V q is greater than VA, the yaw necessary to produce 1.5 “q” could result in overloading other airplane structures, and the maneuver should not be performed.
(6) V LG may be reduced by imposing limitations on the airplane so that Vq is less than VA.
(7) The definitions of the terms used above are equivalent airspeeds, as follows:
VA = Design maneuvering speed
VD = Design diving speed
VLG = Landing gear speed used in the calculation of Vq
VLE = Maximum landing gear extended speed
VLO = Maximum landing gear operating speed
Vq = Speed which results in 1.5 times limit "q" loading
b. If the condition of Item a (5) above exists, substantiation of the landing gear doors and retraction mechanism may be accomplished by static tests, analyses, or a combination of both.
Amendment 23-49 and Subsequent This guidance provides clarification of the requirements for tire burst as related to landing gear and 14 CFR, part 23, §§ 23.729(g) and 23.1309 compliance. The intent of the proposed revision to NPRM 94-21 is given as follows: “This proposal would also add a new Sec.
23.729(g) requiring that if the landing gear bay is used as the location for equipment other than landing gear, the equipment must be designed and installed to minimize damage. On larger airplanes, such as the commuter category, a primary cause of damage to such equipment would be tire-burst. In addition, service history has shown that rocks, water, and slush enter the landing gear bay and cause damage. The equipment on any size airplane should be protected from damage by such external sources.”
The requirement in § 23.729(g) states: “If the landing gear bay is used as the location for equipment other than the landing gear . . .“ ”As used within this requirement, the term landing gear applies to all parts and systems contained in the “LANDING GEAR” section in Subpart D (§§ 23.721 through 23.745) that are specific to the landing gear. For example, wheels, brakes, wheel steering mechanism, and structural portions of the landing gear that are within the gear are all considered part of the “landing gear” for § 23.729(g) compliance.
Systems that act on the landing gear, for example, extension and retraction systems, hydraulic systems, are not considered part of the landing gear itself and should be addressed in § 23.729(g) compliance. Compliance to this section can be by isolation of non-landing gear
51 equipment from the landing gear bay or by protection/shielding of this equipment from the effects of tire burst/loose tread and external forces. Using either of these means of compliance to § 23.729(g) also shows compliance to the § 23.1309 Particular Risk Analysis for non-landing gear equipment.
The effects of tire burst must still be evaluated for § 23.1309 compliance. When showing compliance with § 23.1309 for tire burst, in accordance with § 23.1309(f) (2) and AC 23.1309-1E, only the structural portions of the landing gear are exempt from the § 23.1309 requirements. Addressing external effects as part of the airplane safety analysis is consistent with the FAA advisory material for parts 23, 25, and 29, ARP 4761, and “Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.”
When showing compliance with § 23.1309 for tire burst, it is not appropriate to address compliance by assuming a probability of tire burst occurring. Rather tire burst must be assumed to have occurred(assuming a tire burst probability is inconsistent with the advisory material and accepted industry guidelines). Therefore, an acceptable means of compliance with the tire burst requirements § 23.1309 would be to account for all systems and equipment in the tire burst tests and analysis performed under § 23.729(g). These tests and analyses must be conducted on a conformed test article that includes all systems and components as defined in the type design data. Items identified by either analysis or tire burst tests, or both, as capable of causing hazards to the airplane must be protected or relocated. Therefore, we provide answers to the questions raised as follows:
1. “Do hydraulic, mechanical, and electrical components utilized in any way for retraction/extension of the landing gear doors or control of same need to be protected from the tire burst requirements of § 23.729(g)?”
Yes, unless the § 23.1309 safety assessment shows that damage from tire burst cannot cause a hazard(s) to the airplane. The minimization requirements of § 23.729(g) apply.
2. “If the above items are exempt from § 23.729( g), are they exempt from the Particular Risk Analysis required by § 23.1309.”
While § 23.729(g) applies to the item 1 equipment, tire burst effects should be considered for all landing gear and non-landing gear systems and equipment, except flight structure, as part of § 23.1309 compliance.
EASA AMC effective February 12, 2009, AMC 23.729(g) is acceptable for FAA certification.
23.731 Wheels
See 23.735, Brakes.
The corresponding rule in CAR 3 is CAR 3.361.
The corresponding airworthiness criteria is section 4.26, Airship Design Criteria, FAA-P-8110-2, Change 2.