[Federal Register Volume 70, Number 25 (Tuesday, February 8, 2005)]
[Proposed Rules]
[Pages 6598-6600]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-2319]
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NN301; Notice No. 25-05-01-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: Notice of proposed special conditions.
-----------------------------------------------------------------------
SUMMARY: This notice proposes special conditions for the Boeing Model
747SP airplane. This airplane, as modified by L-3 Communications/
Integrated
[[Page 6599]]
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
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.
DATES: Comments must be received on or before March 25, 2005.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Transport Airplane Directorate, Attn:
Rules Docket (ANM-113), Docket No. NN301, 1601 Lind Avenue SW., Renton,
Washington, 98055-4056; or delivered in duplicate to the Transport
Airplane Directorate at the above address. Comments must be marked:
Docket No. NM301. Comments may be inspected in the Rules Docket
weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.
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:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. The most
helpful comments reference a specific portion of the special
conditions, explain the reason for any recommended changes, and include
supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive, as well as a
report summarizing each substantive public contact with FAA personnel
concerning these special conditions. The docket is available for public
inspection before and after the comment closing date. If you wish to
review the docket in person, go to the address in the ADDRESSES section
of this preamble between 7:30 a.m., and 4 p.m., Monday through Friday,
except Federal holidays.
We will consider all comments we receive on or before the closing
date for comments. We will consider comments filed late if it is
possible to do so without incurring expense or delay. We may change
these special conditions in light of the comments received.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it back to you.
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.
L-3 Communications/Integrated Systems has designed the installation
to fly to 45,000 feet and fly 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.
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, the FAA needs to specify
additional design standards for systems utilizing cryogen liquids to
ensure that a minimum level of safety is maintained.
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 the fuel vent
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 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
[[Page 6600]]
conditions would also apply to the other model under the provisions of
Sec. 21.101.
Novel or Unusual Design Features
The modified Boeing Model 747SP will incorporate the following
novel or unusual design features:
1. Cryogenic fluids (liquid nitrogen and liquid 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.
Discussion
There are no specific regulations that address requirements for the
use of liquid cryogens on board airplanes. To ensure that a minimum
level of safety is achieved equivalent to that intended by the
regulations incorporated by reference, special conditions are needed
for the Boeing Model 747SP airplane.
These special conditions require cryogenic systems to be designed
and installed to preclude or minimize the existence of unsafe
conditions that could result from system leakage, malfunction, or
damage from external sources. In the event of leakage in the cabin
area, ventilation must be provided that is adequate to protect crew and
passengers from asphyxiation. The airplane's structure must also be
protected from contacting the liquids. Rotor burst of high-energy
equipment must be considered and adequate protection must be provided
to protect the liquid containers (either in the cabin or in the aft
telescope area).
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.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Federal Aviation Administration (FAA) proposes the
following special conditions 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 will 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 will provide release of gases to prevent
overpressure of dewars and plumbing lines. The pressure relief valves
shall 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 will 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.
5. An analysis will 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 shall 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 will 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 will be isolated from combustible materials including
grease, oil, and ignition sources.
8. Instructions for continued airworthiness (ICA) will require
periodic inspection of cryogenic components. The ICA will also include
periodic inspection of plumbing insulation to ensure integrity.
9. Shutoff valves will be installed where multiple cryogenic
pressurized storage vessels are connected together by manifolds so that
a leak in one pressurized storage vessel 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 shall account for the worst-case temperature
and material strength properties the components are exposed to in
service.
11. The plumbing installation must be designed to consider 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.
Issued in Renton, Washington, on January 28, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 05-2319 Filed 2-7-05; 8:45 am]
BILLING CODE 4910-13-U