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