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.
23.733 Tires
The corresponding rule in CAR 3 is CAR 3.362.
The corresponding airworthiness criteria is section 4.27, Airship Design Criteria, FAA-P-8110-2, Change 2.
Original Issue and Subsequent (see the following NOTE) The following is a recommended test procedure for installing tires on a part 23 airplane:
1. Inflate an inboard main tire to the minimum allowable inflation pressure for the airplane weight.
2. Inflate the outboard main tire on that sa me landing gear to the maximum allowable inflation pressure for the airplane weight.
3. Using white shoe polish or equivalent, mark a two-inch wide stripe on the brake (inboard) side of the outboard tire sidewall adjacent to the wheel rim.
4. Conduct at least two maximum efforts; non-skidding taxi turns into the minimum inflation side of the airplane.
5. Check for evidence of brake wheel housi ng abrasion contact on the tire sidewall.
NOTE: Above applies to a dual tire installation for landing gear. For a single tire per gear, inflate either side to the minimum pressure and the opposite side to maximum, and turn into the minimum pressure side.
In a revision to Amendment 23-17, the final rule adopted the proposed change in NPRM 75- 10, that added § 23.733(c) with the following explanation: “The proposed rule would require that the selection of tires for installation on retractable landing gear mechanisms take into account the tire production tolerance and size increases that would be expected to result from service. The FAA believes compliance with the proposed rule could prevent accidents that might result from jamming of landing gear mechanisms by oversize tires.”
Tundra Tires
1. PURPOSE. This guidance serves several purposes. First, it summarizes the results of flight tests recommended by the National Transportation Safety Board (NTSB) and conducted by the FAA to examine the effects of tundra tires installed on a Piper PA-18.
Second, it provides information on possible hazards associated with the type of operations common for tundra tire users and potential adverse effects of untested installations.
Third, it provides general information about the certification process for oversized "tundra" tires, as well as an example "compliance checklist" for the installation of such tires on light airplanes that have CAR, part 3 for a certification basis.
2. RELATED READING MATERIAL
a. Part 23, CAR part 3, and CAR part 03.
b. “National Transportation Safety Board (NTSB) Safety Recommendation A-95-13,” dated February 7, 1995.
c. Technical Standard Order (TSO)-C62e , “Aircraft Tires,” September 24, 2006.
d. AC 43.13-1B, Change 1, “Acceptable Methods , Techniques, and Practices—Aircraft Inspection and Repair,” September 27, 2001.
3. BACKGROUND. In Safety Recommendation A-95-13, dated February 7, 1995, the NTSB shared some of their safety concerns about tundra tires with the FAA and requested the possibility of problems with tundra tires be investigated.
The NTSB stated the following:
“Since the early 1960s, hundreds of airplanes operating in Alaska have been equipped with tundra tires, and dozens of versions of tundra tires—some exceeding 35 inches in diameter—have been marketed. The Safety Board is concerned that field approvals and STCs have been granted for use of these tires without flight test or other data on the aerodynamic effects of the tires and wheels. The Piper PA-18 is the airplane most frequently equipped with tundra tires. The Safety Board believes that the FAA should conduct a demonstration flight test to determine the effects of tundra tires on the PA-18s flight characteristics—including cruise, climb, takeoff, and landing performance—and, in both straight and turning flight, stall warning and aircraft stability at or near the critical angle of attack. Further, if the tests of the PA-18 indicate the need, the FAA should take corrective action and expand testing to other airplane types equipped with oversized tires.”
4 SUMMARY OF FLIGHT TEST RESULTS FOR PIPER PA-18 EQUIPPED WITH
TUNDRA TIRES The FAA's flight tests of tundra tires and their results are detailed in Appendix 1 following this guidance. As can be seen in the report, the tundra tire installations on the Piper PA-18 “150” caused no observable adverse effects on stall or stall characteristics during the FAA tests. Although there was some degradation of handling qualities associated with increasing the tire size, the effect was not significant for safety. Rate of climb and cruise speed was degraded with the larger tire sizes; however, the aircraft still met certification requirements. Added tests conducted by an independent Designated Engineering Representative (DER) flight test pilot showed the same lack of effect on stall characteristics with the main landing gear fabric covering removed. It should be remembered that these results are valid only for the Piper PA-18 “150” and for tires no larger than those tested. It should also be noted that, although tundra tires did not cause a safety problem, the stall characteristics of the basic Super Cub (and most other airplanes) make low altitude turning stalls hazardous, especially in uncoordinated flight. Also
55 although washout was not varied during these flight tests, previous FAA experience has shown that stall characteristics are further aggravated when operators of the PA-18 remove the 2.5 degrees of washout at the wing tip, which is not an approved change. This condition will result in a rapid roll when the airplane is stalled during turning flight.
5. POTENTIAL ADVERSE EFFECTS OF TUNDRA TIRE INSTALLATIONS ON
AIRPLANES
a. Performance Tundra tire installations on airplanes may produce one or more of the following effects on performance characteristics:
(1) Increased stall speed.
(2) Reduced stall warning margin.
(3) Reduced rate of climb.
(4) Reduced maximum angle of climb.
(5) Reduced maximum level flight speed.
(6) Reduced cruise speed.
(7) Reduced range.
Tundra tires reduce climb, cruise, and range performance more when installed on relatively “clean,” well streamlined airplanes than they do when installed on less streamlined airplanes.
b. Flight and Ground Handling Characteristics Tundra tire installations on airplanes may produce one or more of the following effects on handling characteristics:
(1) Reduced ability of brakes to hold against takeoff power.
(2 Reduced brake effectiveness during rejected takeoff and braked landing.
(3) Reduced stability and controllability during rejected or balked landing and go around.
(4) Change in either trim range or trim authority, or both.
(5) Reduced directional stability and co ntrol during takeoff and landing ground rolls, with consequent increased tendency to ground loop.