02-12608. Special Conditions: Airbus Industrie, Model A340-500/-600 Airplanes; Ground Loads and Conditions for Center Landing Gear With Four Wheels and Braking Capability

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions.

SUMMARY:

These special conditions are issued for the Airbus Industrie Model A340-500 and -600 airplanes. These airplanes will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. This design feature is associated with the landing gear, in the form of a four-wheeled center landing gear, installed under the fuselage, which functions like a main landing gear in all respects, including the ability to brake. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These proposed special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

EFFECTIVE DATE:

May 10, 2002.

FOR FURTHER INFORMATION CONTACT:

Tim Backman, FAA, ANM-116, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056; telephone [phone]; facsimile [phone].

SUPPLEMENTARY INFORMATION:

Background

On November 14, 1996, Airbus Industrie applied for an amendment to U.S. type certificate (TC) A43NM to include the new models A340-500 and -600. These models are derivatives of the A340-300, which is approved under the same TC.

The Model A340-500 fuselage is a 6-frame stretch of the Model A340-300 and is powered by 4 Rolls Royce Trent 553 engines, each rated at 53,000 pounds of thrust. The airplane has interior seating arrangements for up to 375 passengers, with a maximum takeoff weight (MTOW) of 820,000 pounds. The Model 340-500 is intended for long-range operations and has additional fuel capacity over that of the Model A340-600.

The Model A340-600 fuselage is a 20-frame stretch of the Model A340-300 and is powered by 4 Rolls Royce Trent 556 engines, each rated at 56,000 pounds of thrust. The airplane has interior seating arrangements for up to 440 passengers, with a MTOW of 804,500 pounds.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Airbus Industrie must show that the Model A340-500 and -600 airplanes meet the applicable provisions of the regulations incorporated by reference in TC A43NM or the applicable regulations in effect on the date of application for the change to the type certificate. The regulations incorporated by reference in the type certificate are commonly referred to as the “original type certification basis.” The regulations incorporated by reference in TC A43NM are 14 CFR part 25 effective February 1, 1965, including Amendments 25-1 through 25-63 and Amendments 25-64, 25-65, 25-66, and 25-77, with certain exceptions that are not relevant to these proposed special conditions.

In addition, if the regulations incorporated by reference do not provide adequate standards with respect to the change, the applicant must comply with certain regulations in effect on the date of application for the change. The FAA has determined that the Model A340-500 and -600 airplanes must be shown to comply with Amendments 25-1 through 25-91,with certain FAA-allowed reversions for specific part 25 regulations to the part 25 amendment levels of the original type certification basis.

Airbus has also chosen to comply with part 25 as amended by Amendments 25-92, -93, -94, -95, -97, -98, and -104.

If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 25) do not contain adequate or appropriate safety standards for the Airbus Industrie Model A340-500 and -600 airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of 14 CFR 21.16.

In addition to the applicable airworthiness regulations and special conditions, the Airbus Industrie Model A340-500 and -600 airplanes must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR part 36.

Special conditions, as defined in 14 CFR 11.19, are issued in accordance with § 11.38 and become part of the type certification basis in accordance with 14 CFR 21.101(b)(2).

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same novel or unusual design feature, the special conditions would also apply to the other model under the provisions of 14 CFR 21.101(a)(1).

Novel or Unusual Design Features

The Airbus Model A340-500 and -600 airplanes will incorporate the following novel or unusual design feature: a four-wheel center landing gear with braking ability.

Discussion

The basic A340 included a two-wheel center landing gear which did not have brakes. The purpose of the center landing gear was to assist the main landing gear during ground handling conditions for heavy airplane weights. This center landing gear was not intended for energy absorption during landing, even if it could participate in the impact under certain conditions. Therefore, to provide additional taxi, takeoff, and landing criteria for this arrangement, Special Conditions 25-ANM-69 were issued.

The Model A340-500 and -600 airplanes have a four-wheel center landing gear which functions in all respects like a main landing gear, including braking capabilities. Because the speeds and weights of the Model A340-500 and -600 airplanes are greater than that of the basic A340, redesign of the center landing gear was necessary. As a result, the current rules, applying to the original two-wheel center landing gear, are inadequate.

Discussion of Comments

Notice of proposed special conditions No. 25-02-03-SC for the Airbus Industrie Model A340-500 and -600 airplanes was published in the Federal Register on March 20, 2002 (67 FR 12903). No comments were received, and the special conditions are adopted as proposed.

Applicability

As discussed above, these special conditions are applicable to the Airbus Model A340-500 and -600 airplanes. Should Airbus Industries apply at a later date for a change to the type certificate to include another model incorporating the same novel or unusual design feature, the special conditions would apply to that model as well under the provisions of § 21.101(a)(1).

Under standard practice, the effective date of final special conditions would be 30 days after the date of publication in the Federal Register; however, as the certification date for the Airbus Model A340-500 and A340-600 airplanes is imminent, the FAA finds that good cause exists to make these special conditions effective upon issuance.

Conclusion

This action affects only certain novel or unusual design features of the center landing gear on the Model A340-500 and A340-600 airplanes. It is not a rule of general applicability, and it affects only the applicant who applied to the FAA for approval of these features on the airplane.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety
• Reporting and recordkeeping requirements

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Special Conditions

Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the type certification basis for Airbus Model A340-500 and A340-600 airplanes.

The following special conditions are issued in lieu of the previously issued special conditions, “Ground Load Conditions for Center Landing Gear,” recorded as item 10 of Special Conditions: Airbus Industrie Model A340 Series Airplanes [Docket No. NM-75, Special Conditions No. 25-ANM-69]:

1. Ground Load Conditions for Center Landing Gear. Notwithstanding § 25.477, the requirements of § 25.473 and §§ 25.479 through 25.485 apply, except as noted:

(a) In addition to the requirements of § 25.473, “Landing load conditions and assumptions,” and § 25.479, “Level landing conditions,” landing should be considered on a level runway and on a runway having a convex upward shape that may be approximated by a slope of 1.5 percent at main landing gear stations. The maximum loads determined from these two conditions must be applied to each main landing gear and to the center landing gear.

(b) In addition to the requirements of § 25.483, “One gear landing conditions,” the condition represented by Figure 1 also applies:

(c) In lieu of the requirements of § 25.485, “Side load conditions,” the following apply:

(1) The airplane is considered to be in the level attitude with only the main and center wheels contacting the ground.

(2) Vertical reactions of one-half of the maximum vertical reaction obtained at each main and center gear in the level landing conditions should be considered. The vertical loads must be combined with side loads as follows: for the main gear, 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward; for the center gear, 0.7 of the vertical reaction acting in the same direction as main gear side loads. These loads are assumed to be applied at the ground contact point and to be resisted by the inertia of the airplane. The drag loads may be assumed to be zero.

(d) In addition to § 25.489, “Ground handling conditions,” the airplane should be considered to be on a level runway and on a runway having a convex upward shape that may be approximated by a slope of 1.5 percent at main landing gear stations. The ground reactions must be distributed to the individual landing gear units in a rational or conservative manner.

(e) In addition to the requirements of § 25.493(d), “Braked roll conditions,” the sudden application of maximum braking effort must be defined taking into account the behavior of the braking system. Failure conditions of the braking system not shown to be extremely improbable must be analyzed in accordance with the following criteria:

(1) At the time of occurrence. A realistic scenario, including pilot corrective actions, must be established to determine the loads occurring at the time of failure and immediately after failure.

(i) For static strength substantiation, these loads multiplied by an appropriate factor of safety that is related to the probability of occurrence of the failure are ultimate loads to be considered for design. The factor of safety (F.S.) is defined in Figure 2 as follows:

(ii) For residual strength substantiation, the airplane must be able to withstand two thirds of the ultimate loads defined in paragraph (e)(1)(i).

(iii) Failures of the system that result in forced structural vibrations (oscillatory failures) must not produce loads that could result in detrimental deformation of primary structure.

(2) Consideration of certain failure conditions may be required by other sections of part 25, regardless of calculated system reliability. Where analysis shows the probability of these failure conditions to be less than 10⁻⁹, criteria other than those specified in this paragraph may be used for structural substantiation to show continued safe flight and landing.

(3) Warning considerations. For system failure detection and warning, the system must be checked for failure conditions, not extremely improbable, that degrade the structural capability below the level required by part 25 or significantly reduce the reliability of the remaining system. The flightcrew must be made aware of these failures before flight. Certain elements of the control system, such as mechanical and hydraulic components, may use special periodic inspections, and electronic components may use daily checks, in lieu of warning systems to achieve the objective of this requirement. These certification maintenance requirements must be limited to components that are not readily detectable by normal warning systems and where service history shows that inspections will provide an adequate level of safety.

(4) Dispatch with known failure conditions. If the airplane is to be dispatched in a known system failure condition that affects structural performance, or affects the reliability of the remaining system to maintain structural performance, then the provisions of these special conditions must be met for the dispatched condition and for subsequent failures. Flight limitations and expected operational limitations may be taken into account in establishing Qj as the combined probability of being in the dispatched failure condition and the subsequent failure condition for the safety margins in Figure 3. These limitations must be such that the probability of being in this combined failure state and then subsequently encountering limit load conditions is extremely improbable. No reduction in these safety margins is allowed if the subsequent system failure rate is greater than 10⁻³ per hour. Figure 3 follows:

(f) In lieu of the requirements of § 25.495, “Turning,” the following apply:

(1) The airplane is assumed to execute a steady turn by nose gear steering, or by application of sufficient differential power, so that the limit load factors applied at the center of gravity are 1.0 vertically and 0.5 laterally.

(2) The airplane must be designed for the condition prescribed in paragraph (f)(1), taking into account:

(i) The effects of tire characteristics on the sharing of lateral loads on each tire of the landing gear system, and

(ii) The effect of airframe and landing gear flexibility on the sharing of loads on the different legs of the landing gear system.

(g) In lieu of the requirements of § 25.503, “Pivoting,” the following apply:

(1) The main and center gear units and supporting structure must be designed for the scrubbing or torsion loads, or both, induced by pivoting during ground maneuvers produced by:

(i) Towing at the nose gear, no brakes applied, and

(ii) Application of symmetrical or unsymmetrical forward thrust to aid pivoting and with or without braking by pilot action on the pedals.

(2) The airplane is assumed to be in static equilibrium, with the loads being applied at the ground contact points.

(3) The limit vertical load factor must be 1.0, and:

(i) For wheels with locked brakes applied by pilot action on the pedals, the coefficient of friction must be 0.8.

(ii) For wheels with brakes not applied, the ground tire reactions must be based on reliable tire data.

(4) The failure conditions must be analyzed in accordance with paragraph (e) of these Special Conditions.

(h) In lieu of paragraph (b) of § 25.723 “Shock absorption tests,” the center landing gear should not fail in a test demonstrating its reserve energy absorption capacity at design landing weight, assuming airplane lift no greater than the airplane weight acting during a 12-feet-per-second airplane landing impact, taking into account both main and center gear acting during the impact. Landing should be considered on a level runway or a runway having a convex upward shape that may be approximated by a slope of 1.5 percent with the horizontal at main landing gear stations, whichever is the most critical.

Issued in Renton, Washington, on May 10, 2002.

Ali Bahrami,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.