```

[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
```