Special Conditions: Boeing Model 747SP; NASA Stratospheric Observatory for Infrared Astronomy (SOFIA); Cryogenic Systems Using Liquid Nitrogen and Liquid Helium, 33335-33337 [05-11324]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 70, Number 109 (Wednesday, June 8, 2005)]
[Rules and Regulations]
[Pages 33335-33337]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-11324]



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Federal Register / Vol. 70, No. 109 / Wednesday, June 8, 2005 / Rules 
and Regulations

[[Page 33335]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NN301; Special Conditions No. 25-290-SC]


Special Conditions: Boeing Model 747SP; NASA Stratospheric 
Observatory for Infrared Astronomy (SOFIA); Cryogenic Systems Using 
Liquid Nitrogen and Liquid Helium

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Boeing Model 747SP 
airplane. This airplane, as modified by L-3 Communications/Integrated 
Systems, of Waco, Texas, will have novel and unusual design features 
associated with cryogenic systems using liquid nitrogen and liquid 
helium. 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.

DATES: Effective July 8, 2005.

FOR FURTHER INFORMATION CONTACT: Kathi Ishimaru, FAA, Propulsion/
Mechanical Systems Branch, ANM-112, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, 
Washington, 98055-4056; telephone (425) 227-2674; facsimile (425) 227-
1232.

SUPPLEMENTARY INFORMATION:

Background

    On March 17, 1997, L-3 Communications/Integrated Systems, 7500 
Maehr Road, Waco, Texas 76705, applied for a Supplemental Type 
Certificate (STC) to modify a Boeing Model 747SP airplane for use as a 
flying observatory. This airplane will fly in the stratosphere to 
altitudes of 45,000 feet and use infrared technology to observe objects 
in space. The airplane is a stratospheric observatory for infrared 
astronomy or SOFIA. The modification consists of the installation of a 
2.5-meter telescope, scientist workstations, and containment vessels 
for liquid helium and nitrogen (liquid converters, valves, evaporating 
coils, liquid lines, regulators, indicators, fittings, etc). Various 
science instruments (each having their own airworthiness approval), 
each weighing approximately 800 pounds, located in the workstation 
area, can be attached to the telescope for a specific mission (one per 
mission only).
    The mission of the SOFIA airplane is to collect infrared signals. 
The observatory collects very weak infrared signals that were emitted 
by distant objects in space thousands of years ago. These signals are 
focused through the telescope onto sensors in the science instrument 
which is located on the cabin side of the telescope. To detect the weak 
infrared signals, the detectors in these sensors are cooled to 
temperatures near absolute zero by the use of cryogenic fluids. These 
fluids are contained in vessels similar to vacuum bottles. Their design 
and installation are covered by these special conditions. These 
extremely cold environments can only be produced by cryogenic liquids. 
The SOFIA observatory depends on liquid helium and nitrogen to chill 
the internal passageways of the detector systems. The amount of 
cryogens used here is small.
    Cryogens, in a much greater quantity, are used in the area where 
the telescope mirror is installed. Liquid nitrogen is converted to a 
gas and circulated around the mirror to pre-cool it to prevent it from 
fogging up as it goes from a warm moist atmosphere on the ground to the 
cold dry atmosphere at high altitudes.
    The modified Boeing Model 747SP airplane, with the L-3 
Communications/Integrated Systems design will fly to 45,000 feet and in 
a gradual arc pattern for extended periods of time. Additionally, 
various science instruments will be installed under this STC or similar 
STCs, which will be referenced back to this STC.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, L-3 Communications/
Integrated Systems must show that the modified Boeing Model 747SP 
airplane, as changed, continues to meet the applicable provisions of 
the regulations incorporated by reference in Type Certificate No. 
A20WE, or the applicable regulations in effect on the date of 
application for the change. The regulations incorporated by reference 
in the type certificate are commonly referred to as the ``original type 
certification basis.''
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the Boeing Model 747SP airplane 
modified by L-3 Communications/Integrated Systems because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Boeing Model 747SP must comply with (1) either the ``No 
Acoustical Change'' provisions of Sec.  21.93(b) or 14 CFR part 36, as 
amended by Amendments 36-1 through 36-23 and any later amendments that 
are effective 5 years prior to the STC approval date, and (2) either 
the ``No Emissions Change'' provisions of Sec.  21.93(c) or 14 CFR part 
34, as amended by Amendments 34-1 through 34-3.
    Special conditions, as defined in 14 CFR 11.19, are issued in 
accordance with Sec.  11.38 and become part of the type certification 
basis in accordance with Sec.  21.101.
    Special conditions are initially applicable to the model for which 
they are issued. Should L-3 Communications/Integrated Systems apply at 
a later date for a supplemental type certificate to modify any other 
model included on the same type certificate to incorporate the same 
novel or unusual design feature, these special conditions would also 
apply to the other model under the provisions of Sec.  21.101.

Novel or Unusual Design Features

    The modified Boeing Model 747 SP will incorporate the following 
novel or unusual design features:

[[Page 33336]]

    1. Cryogenic fluids (nitrogen and helium) contained in the science 
instrument in the cabin compartment. The cryogenic gases could cause an 
asphyxiation hazard to the crew and passengers.
    2. The cryogens (liquid nitrogen), stored for chilling the mirror 
during ascent, might come in contact with the airplane's structure, 
which could cause damage to the surrounding structural areas.
    The cryogenic systems must be designed and installed to ensure that 
no failure of the systems, including a leak in any part of the systems, 
would prevent continued safe flight and landing of the airplane.
    There are no specific regulations that address the design and 
installation of liquid nitrogen systems and liquid helium systems. 
Existing requirements such as 14 CFR 25.1309 and 25.1438(b) are 
applicable to this installation. However, these regulations do not 
address the effect of cryogenic gases of passengers or crew and 
aircraft structure. The FAA needs to specify additional design 
standards, which specifically address these novel or unusual design 
features for systems utilizing cryogen liquids to ensure that a minimum 
level of safety is maintained, establishing a level of safety 
equivalent to the current regulations.

Discussion of Comments

    Notice of proposed special conditions No. 25-05-01-SC for the 
Boeing Model 747 SP; NASA Stratospheric Observatory For Infrared 
Astronomy (SOFIA) airplanes was published in the Federal Register on 
February 8, 2005 (70 FR 6598). No comments were received, and the 
special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Boeing 747SP airplane. Should L-3 Communications/Integrated Systems 
apply at a later date for a supplemental type certificate to modify any 
other model included on Type Certificate No. A20WE to incorporate the 
same novel or unusual design feature, these special conditions would 
apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on the Boeing Model 747SP airplane. 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 record keeping 
requirements.


0
The authority citation for these special conditions is as follows:

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

The Special Conditions

0
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 Boeing Model 747SP airplane as 
modified by L-3 Communications/Integrated Systems, of Waco, Texas:
    1. Occupied compartments that contain cryogenic fluids must be 
provided with a means of ventilation to prevent the accumulation of 
cryogenic gases to a level that may cause an asphyxiation hazard to the 
crew or passengers.
    2. Cryogen dewars must be limited to a maximum capacity of 70 
liters of liquid nitrogen and 80 liters of liquid helium. These limits 
placed on the instrument are adequate to allow the instrument to 
perform the mission.
    3. Pressure relief valves must provide release of gases to prevent 
overpressure of dewars and plumbing lines. The pressure relief valves 
must be vented overboard through a drain in the bottom of the airplane 
unless it is substantiated that the valves can be safely vented inside 
the airplane. The cryogenic system must be designed to prohibit the 
pressure relief valves from freezing due to air condensing and 
freezing.
    4. Cryogenic equipment and plumbing installations must be designed 
such that a spill, rupture, or any other failure to contain the liquid 
cryogen will not result in direct contact of the liquid cryogen with 
load bearing structure or critical airplane equipment that is essential 
for the continued safe flight and landing of the airplane. Because of 
the extremely low temperature of the liquid cryogen, direct contact may 
adversely affect the material properties and integrity of load bearing 
structure. Direct contact of liquid cryogen with critical airplane 
equipment may cause failure of the equipment to perform its intended 
function.
    5. An analysis must be accomplished to substantiate that the 
airplane will not be overpressurized in the event of a catastrophic 
failure of all the dewars containing cryogenic fluid.
    6. The location of the cryogenic equipment and plumbing 
installations must minimize the risk of damage due to an uncontained 
rotor or fan blade failure. All equipment containing high-energy rotors 
must be considered, such as turbine engines, auxiliary power units, ram 
air turbines, electric/pneumatic engine starters, air cycle machines, 
and certain cooling fans. In addition to properly locating the 
cryogenic system, operational procedures and shields may be used to 
minimize the risk of damage. New equipment containing high-energy 
rotors whose uncontained failure could damage the cryogenic system must 
comply with Sec.  25.1461, Amendment 25-41.
    7. The cryogenic system must be designed to minimize condensation 
of the atmospheric air, which could result in a liquid enriched with 
oxygen due to nitrogen having a lower boiling point than oxygen. Any 
condensation from system components or lines must be collected by drip 
pans, shields, or other suitable collection means and drained overboard 
through a drain fitting separate from the pressure relief vent 
fittings, if equipped for compliance with Special Condition No. 3. The 
condensation must be isolated from combustible materials including 
grease, oil, and ignition sources.
    8. Instructions for continued airworthiness (ICA) must require 
periodic inspection of cryogenic components. The ICA must also include 
periodic inspection of plumbing insulation to ensure integrity.
    9. Shutoff valves must be installed where multiple cryogenic 
pressurized storage vessels are connected together by manifolds so that 
a leak in one pressurized storage vessel can be isolated and will not 
allow leakage of the cryogenic fluids from any other pressurized 
storage vessel.
    10. Cryogenic components must be burst pressure tested to 3.0 
times, and proof pressure tested to 1.5 times the maximum normal 
operating pressure. Tests must account for the worst-case combination 
of temperature and material strength properties that the components are 
exposed to in service.
    11. The plumbing installation must be designed to account for 
thermal expansion and thermally induced stresses.
    12. The cryogenic system must be protected from unsafe temperatures 
and located where the probability of hazards of rupture in a crash 
landing are minimized.
    13. The proof of strength of airframe load bearing structure in the 
vicinity of cryogenic equipment and plumbing must account for 
temperature extremes, and the effect on the strength of materials, 
resulting from carriage of cryogenic fluids.


[[Page 33337]]


    Issued in Renton, Washington, on May 26, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-11324 Filed 6-7-05; 8:45 am]
BILLING CODE 4910-13-P