Federal Aviation Administration (FAA), DOT.
Final special conditions.
These special conditions are issued for the Embraer S.A., Model EMB-500 airplane. This airplane will have a novel or unusual design feature(s) associated with high fuel temperature. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These 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: June 10, 2008.Start Further Info
FOR FURTHER INFORMATION CONTACT:
Peter L. Rouse, Federal Aviation Administration, Aircraft Certification Service, Small Airplane Directorate, ACE-111, 901 Locust, Kansas City, Missouri, 816-329-4135, fax 816-329-4090.End Further Info End Preamble Start Supplemental Information
On October 5, 2005, Embraer S.A. applied for a type certificate for their new Model EMB-500. The Model EMB-500 is a normal category, low-winged monoplane with “T” tailed vertical and horizontal stabilizers, retractable tricycle type landing gear and twin turbofan engines mounted on the aircraft fuselage. Its design characteristics include a predominance of metallic construction. The maximum takeoff weight is 9,965 pounds, the VMO/MMO is 275 KIAS/M 0.70 and maximum altitude is 41,000 feet.
Fuel temperatures on the Embraer EMB 500 are higher than envisioned by 14 CFR part 23. The rule governing fuel system hot weather operation is 14 CFR part 23, § 23.961, and the rule requires the following:
Each fuel system must be free from vapor lock when using fuel at its critical temperature, with respect to vapor formation, when operating the airplane in all critical operating and environmental conditions for which approval is requested. For turbine fuel, the initial temperature must be 110 °F, −0°, +5° or the maximum outside air temperature for which approval is requested, whichever is more critical.
During other airplane certification projects, the fuel system temperatures associated with the PW600 series turbofan engines were much higher than those previously encountered on other engines. The engine oil/fuel heat fuel system includes an exchanger that cools the oil and heats the fuel. Consequently, the motive flow fuel that is returned to the airplane from the engine is hot and heats the airplane wing fuel and tank. As a result, on the PW615F, the engine inlet maximum fuel temperature was increased from a development value of 126 °F (52 °C) to an initial (Transport Canada) certification value of 172 °F (78 °C) for kerosene type fuels.
Initial concerns regarding the safe operation of the airplane with fuel temperatures significantly greater than 110 °F are identified as:
- Fuel degradation with resultant byproducts at high temperatures
- Operation with the higher vapor liquid ratios
- Fuel system component qualification at the higher temperatures
- Solubility of water in fuel
- Microbial growth
- Fuel tank material/surrounding structure compatibility with the elevated temperatures
- Service and maintenance personnel susceptibility to burns
An initial review of FAA experience regarding airplane fuel temperatures identifies that for large part 25 aircraft, fuel temperature upper limits are characterized by § 25.961 values, i.e. 110-120 °F. Operationally, the buildup of vapor pockets within fuel lines has been an issue from this perspective for large transport category airplanes. A summary of the maximum engine inlet fuel temperatures for engines used in part 23 and part 25 business jet airplanes that are FAA certified follows:
|Engine Model||Sea level maximum inlet fuel temperature|
|PWC615F||126 F (52 C) draft IM|
|PWC615F||172 F (78 C) Transport Canada|
|PWC615F||190 F (88 C)|
|530A, 535A||135 F (57 C)|
|545A||135 F (57 C)|
|305A||135 F (57 C)|
|308||135 F (57 C)|
|JT15D-4, -4B, -4D||135 F (57 C)|
|FJ44-3A||200 F (93 C)|
|FJ44-2A||135 F (57 C)|
|FJ44-1B||135 F (57 C)|
|TFE731-2/-3||135 F (57 C)|
|TFE731-20||135 F (57 C)|
CAR part 3, as amended to May 15, 1956, defined the maximum anticipated summer air temperatures in § 3.583; “The maximum anticipated summer air temperature shall be considered to be 100 °F at sea level and to decrease from this value at the rate of 3.6 °F per thousand feet above sea level.” Concurrently, § 3.438 required that “* * * fuel system features conducive to vapor formation shall be demonstrated to be free from vapor lock when using fuel at a temperature of 110 °F under critical operating conditions.” Building from CAR part 3, 14 CFR part 23 envisioned maximum fuel temperatures at or near 110 °F as set forth in 14 CFR part 23, § 23.961. The turbine fuel temperature requirement for hot weather operation is 110 −0, +5 °F, or the maximum outside air temperature for which approval is requested, whichever is more critical. Engine heat rejection such that the airplane fuel temperature is characterized by engine heat rejection rather than ambient air temperature is a new and novel design that was not envisioned by 14 CFR part 23.
14 CFR part 23 certification experience to date has shown that hot weather certification testing with 110 °F fuel temperatures is adequate for fuel system operations for fuel tank fuel temperatures characterized by ambient air temperatures including cooling as a result of the atmospheric temperature lapse rate. Heating that increases the airplane fuel system operational temperatures introduces several fuel Start Printed Page 34844system concerns. Each must be shown to be acceptable. Compliance by design (i.e. lack of ability to shutoff the engine motive flow) may be utilized although associated type certificate data sheet information may also be necessary to assure future system changes are compliant.
A special condition for the higher fuel system temperatures of the Embraer EMB 500 airplane was proposed. The special condition requires the compliance to 14 CFR part 23, § 23.961, fuel system hot weather operation test temperature to be commensurate with the highest fuel temperature expected at the maximum outside air temperature for which approval is requested.
Type Certification Basis
If the Administrator finds that the applicable airworthiness regulations (i.e., 14 CFR part 23) do not contain adequate or appropriate safety standards for the Model EMB-500 because of a novel or unusual design feature, special conditions are prescribed under § 21.16.
In addition to the applicable airworthiness regulations and special conditions, the Model EMB-500 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, and the FAA must issue a finding of regulatory adequacy under § 611 of Public Law 92-574, the “Noise Control Act of 1972.”
Special conditions, as appropriate, as defined in § 11.19, are issued under § 11.38, and become part of the type certification basis under § 21.17(a).
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, the special conditions would also apply to the other model under § 21.101(a).
Novel or Unusual Design Features
The Model EMB-500 will incorporate the following novel or unusual design features: High Fuel Temperatures.
Discussion of Comments
Notice of proposed special conditions No. 23-07-05-SC for the Embraer S.A., Model EMB-500 airplanes was published on January 23, 2008 (73 FR 3881). No comments were received, and the special conditions are adopted as proposed.
As discussed above, these special conditions are applicable to the Model EMB-500. Should Embraer S.A. apply later 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 § 21.101(a).
This action affects only certain novel or unusual design features on one model, Model EMB-500, of 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.Start List of Subjects
List of Subjects in 14 CFR Part 23End List of Subjects
The authority citation for these special conditions is as follows:
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 the Embraer S.A. Model EMB-500 airplanes.
1. SC § 23.961
Instead of compliance with § 23.961, the following apply:
Each fuel system must be free from vapor lock when using fuel at its critical temperature, with respect to vapor formation, when operating the airplane in all critical operating and environmental conditions for which approval is requested. For turbine fuel, the initial temperature must be the highest fuel temperature expected at the maximum outside air temperature for which approval is requested.Start Signature
Issued in Kansas City, Missouri on June 10, 2008.
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. E8-13830 Filed 6-18-08; 8:45 am]
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