Security Related Considerations in the Design and Operation of Transport Category Airplanes, 63867-63880 [E8-25476]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 73, Number 209 (Tuesday, October 28, 2008)]
[Rules and Regulations]
[Pages 63867-63880]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-25476]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25 and 121

[Docket No. FAA-2006-26722; Amendment Nos. 25-127, 121-341]
RIN 2120-AI66


Security Related Considerations in the Design and Operation of 
Transport Category Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: The rule adopts several standards of the International Civil 
Aviation Organization (ICAO) and requires manufacturers to incorporate 
certain security features in the design of new transport category 
airplanes. Specifically, manufacturers of affected

[[Page 63868]]

airplanes must design flightdecks that are protected from penetration 
by projectiles and intrusion by unauthorized persons. The flightdeck, 
passenger cabin, and cargo compartments of these aircraft must be 
protected from the effects of detonation of an explosive or incendiary 
device. The rule also requires that manufacturers of new transport 
category airplanes design a ``least risk bomb location'' and that 
operators of certain existing airplanes designate such a location.

DATES: These amendments become effective November 28, 2008. The 
Director of the Federal Register approved the incorporation by 
reference of certain publications listed in this rule as of the 
November 28, 2008 effective date of this rule.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this final rule, contact: Jeff Gardlin, FAA Airframe and Cabin Safety 
Branch, ANM-115, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington 98055; telephone 
(425) 227-2136; facsimile (425) 227-1149; e-mail: jeff.gardlin@faa.gov. 
For legal questions concerning this final rule, contact: Gary Michel, 
Regulations Division, AGC-200, FAA Office of the Chief Counsel, 800 
Independence Avenue, SW., Washington DC, 20591; telephone (202) 267-
3148; e-mail: gary.michel@faa.gov.

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in 
Title 49 of the United States Code. Subtitle I, Section 106, describes 
the authority of the FAA Administrator. Subtitle VII, Aviation 
Programs, describes in more detail the scope of the agency's authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing minimum 
standards required in the interest of safety for the design and 
performance of aircraft. This regulation is within the scope of that 
authority because it prescribes new safety standards for the design of 
transport category airplanes.

I. Background

A. Summary of the NPRM

    On January 5, 2007, the FAA published a notice of proposed 
rulemaking (NPRM) entitled ``Security Related Considerations in the 
Design and Operation of Transport Category Airplanes.'' \1\ The FAA 
proposed to amend part 25 to specify design standards for new transport 
category airplanes in order to increase security for passengers and 
flightcrew.
---------------------------------------------------------------------------

    \1\ 72 FR 630.
---------------------------------------------------------------------------

    For airplanes required by operating rules to have a flightdeck 
door, the FAA proposed standards to protect the flightdeck from 
forcible intrusion by unauthorized persons or penetration by small arms 
fire or fragmentation devices. The NPRM also proposed that airplanes 
with a certificated passenger seating capacity of more than 60 persons 
or a maximum certificated gross takeoff weight of over 100,000 pounds 
must be designed to limit the effects of an explosive or incendiary 
device by:
    1. Providing means to protect the flightdeck and the passenger 
compartment from smoke, fumes, and noxious gases.
    2. Requiring fire suppression systems for cargo compartments be 
designed to withstand certain impacts or loads--unless they are either 
redundant and separated from one another by a specified distance or 
installed remotely from the cargo compartment.
    3. Designating a ``least risk bomb location'' (LRBL) where a bomb 
or other explosive device discovered in-flight could be placed, so if 
it were to detonate, flight-critical structures and systems would be 
protected from damage as much as possible.
    4. Ensuring redundant airplane systems necessary for continued safe 
flight and landing are either physically separated by a certain 
distance or otherwise designed to permit continued safe flight and 
landing in the aftermath of some event.
    5. Creating interior features of the cabin that make it more 
difficult to conceal weapons, explosives, or other such objects and 
easier to find such items by a simple search.
    The FAA also proposed to amend part 121 to require operators of 
existing airplanes with a passenger seating capacity of more than 60 
persons designate a least risk bomb location. The public comment period 
on the NPRM closed on April 5, 2007.
    The NPRM noted the requirements of this rule are not intended to be 
applied to airplanes operated for private use. Though the FAA 
specifically sought input, we received no comments on this subject. 
Since publication of the NPRM, we have also published NPRM 07-13 \2\, 
proposing certain alternative requirements for private use airplanes. 
We further intend to exclude Sec.  25.795 from the final rule that 
results from the ``private use'' NPRM. This action is consistent with 
our previously stated intentions.
---------------------------------------------------------------------------

    \2\ 72 FR 38732, (July 13, 2007).
---------------------------------------------------------------------------

B. Summary of the Final Rule

    This rule amends part 25 to require manufacturers design certain 
new transport category airplanes to increase security for passengers 
and the flightcrew. The rule specifies design standards to protect the 
flightdeck from forcible intrusion by persons or from penetration by 
small arms fire or fragmentation devices. It also requires the design 
provide means to limit the effects of detonation of an explosive or 
incendiary device by (1) limiting entry of smoke, fumes, and noxious 
gases into the flightdeck or the passenger cabin; (2) meeting specified 
standards for all components of fire suppression systems in cargo 
compartments; (3) establishing an LRBL; (4) physically separating 
certain redundant airplane systems or otherwise designing them to 
continue to function in the event of a detonation; and (5) providing 
interior features that make it harder to conceal weapons, explosives, 
or other objects and easier to detect such objects by a simple search 
of the airplane cabin.
    This rule also amends part 121 to require operators of certain 
existing airplanes designate a least risk bomb location.

C. Summary of Comments

    The FAA received 31 comments on the proposed rule. Commenters 
included airplane manufacturers, airlines, aviation associations, and 
individuals, including students and commercial pilots. Most of the 
comments supported the proposed rule; several commenters also had 
suggestions for change.
    As provided in the original tasking statement to the Aviation 
Rulemaking Advisory Committee (ARAC), certain comments we received were 
referred to the Design for Security Harmonization Working Group. Those 
comments pertained to the following proposed sections in the NPRM:
    1. In Sec.  25.795(b)(3)(iii), delete the requirement to withstand 
``a 6-inch displacement from a single point source applied anywhere 
along the distribution system because of support structure 
displacements or adjacent materials displacing against the distribution 
system.''
    2. In Sec.  25.795(b)(2), clarify those flight and dispatch regimes 
under which smoke protection is not required.
    3. In Sec.  25.795(c)(2), further explain the relation of system 
separation to several existing regulations.

[[Page 63869]]

    4. In Sec.  25.795(c)(2), explain how measurement of the separation 
distance is accomplished.
    5. In Sec.  25.795(c)(3), define an object size to facilitate 
interior searches.
    Comments received on these and other sections of the NPRM are 
considered in detail in the following discussion of this final rule.

II. Discussion of Final Rule

A. Overview

    For more than 50 years, terrorist acts--including hijackings and 
detonation of explosive devices--have targeted airplanes.
1. ICAO Design Standards To Increase Security
    In response to a number of airplane bombings and hijackings that 
occurred in the 1960s, 1970s, and early 1980s, the International 
Federation of Airline Pilots Association developed proposals regarding 
design standards for increased security in airplanes. The association 
submitted the proposals to the International Civil Aviation 
Organization (ICAO), a specialized agency of the United Nations charged 
with development of international standards for safety and security of 
civil aviation. ICAO airworthiness standards affecting airplane design 
are contained in Annex 8 of the Convention on International Civil 
Aviation. ICAO in turn, solicited comments on the proposals from its 
member countries and aviation organizations.
    On December 21, 1988, a terrorist's bomb exploded in mid-air on Pan 
American World Airways Flight 103 from London to New York City. The 
explosion in the forward cargo hold of the Boeing Model 747 airplane 
occurred over Lockerbie, Scotland, killing all 259 people onboard and 
11 people on the ground.
    As a result of this catastrophic event, the effort to establish 
design standards for increased security gained impetus. Within several 
months of the explosion on Flight 103, ICAO formed a study group called 
Incorporation of Security into Aircraft Design (ISAD). The study group 
included representatives of the airworthiness authorities of the United 
States, the United Kingdom, France, Germany, Brazil, and Russia. Also 
included were representatives of the International Federation of 
Airline Pilots Association, the International Coordinating Council of 
Aerospace Industries Associations, and the International Air Transport 
Association.
    The task of ISAD was to consider the existing proposals and 
recommend design standards that were to be incorporated into Annex 8. 
Ultimately, ISAD recommended design standards pertaining to the 
following:
    1. Survivability of systems.
    2. Suppression of fire in cargo compartments.
    3. Protection from smoke and fumes in the flightdeck and the 
passenger cabin.
    4. Design of an LRBL.
    5. Protection of the flightdeck from penetration by small arms fire 
or shrapnel.
    6. Design of interior features to deter concealment of weapons, 
explosives, or other objects and facilitate searching for them.
    On March 12, 1997, ICAO adopted the recommended standards as 
Amendment 97 to Annex 8, and the member countries subsequently approved 
those standards. All but one of the standards became effective 3 years 
after their adoption. The exception was the standard requiring 
identification of an LRBL, which became effective immediately. The 
identification of an LRBL was already common practice in the aviation 
industry and had been applied as an operational standard rather than a 
design standard.
    Generally, Annex 8 standards do not apply directly to the design of 
an airplane, but are implemented by adoption into the airworthiness 
regulations of ICAO's member countries. As a signatory to the 
Convention which established ICAO, the United States is required to 
implement the Annex 8 rules into our national airworthiness regulations 
to the extent practicable.\3\
---------------------------------------------------------------------------

    \3\ Because we have not yet incorporated these ICAO standards 
into our regulations, the United States (like all other states of 
manufacture) has filed ``differences'' with ICAO regarding the 
design for security provisions of Annex 8. Adoption of this final 
rule removes these differences with the ICAO standards.
---------------------------------------------------------------------------

2. ARAC's Recommendations Pertaining to Design for Security \4\
---------------------------------------------------------------------------

    \4\ The FAA formally established the Aviation Rulemaking 
Advisory Committee on January 22, 1991, to provide advice and 
recommendations about FAA's safety-related rulemaking (56 FR 2190).
---------------------------------------------------------------------------

    In addition to participating in the development of international 
standards through ICAO, a high priority for the FAA is maintaining 
harmonized standards between the United States and Europe. This 
harmonization is achieved through the Aviation Rulemaking Advisory 
Committee (ARAC) composed of 66 member organizations providing 
extensive knowledge and expertise on a wide range of aviation matters.
    In 1999, the FAA tasked ARAC to propose regulations incorporating 
security measures into airplane design.\5\ The proposed regulations 
were to be based on Amendment 97 to Annex 8. The task was assigned to 
the Design for Security Harmonization Working Group, incorporating 
members from the aviation industry and the governments of Europe, the 
United States, Brazil, and Canada.
---------------------------------------------------------------------------

    \5\ 64 FR 57921, (October 27, 1999).
---------------------------------------------------------------------------

    In April 2001, after several airlines reported incidents of 
flightdeck intrusion by aggressive passengers, the FAA tasked ARAC to 
propose harmonized regulations to improve the intrusion resistance of 
the flightdeck.\6\ This task was also assigned to the Design for 
Security Harmonization Working Group.
---------------------------------------------------------------------------

    \6\ 66 FR 31273, (June 11, 2001).
---------------------------------------------------------------------------

    The working group proposed harmonized regulations for implementing 
security safeguards into the design of new transport category 
airplanes. The working group submitted its recommendations to ARAC 
which voted in favor of submitting the recommendations to the FAA.
3. Legislation and Rulemaking After the Terrorist Attacks of 9/11
    Several months after the terrorist attacks on September 11, 2001, 
Congress passed the Aviation and Transportation Security Act. Among 
other provisions, the Act directed that--for airplanes required to have 
a door between the flightdeck and the passenger compartment--the FAA 
issue an order requiring strengthening of the door so that it could not 
be forced open from the passenger side.
    On January 15, 2002, the FAA published Amendment No. 25-106.\7\ The 
rule amended 14 CFR 25 to add new Sec.  25.795, Security 
considerations. Paragraph (a) Protection of flightdeck specified that, 
if a flightdeck door were required by operating rules, the door 
installation must resist forcible intrusion by unauthorized persons and 
penetration by small arms and fragmentation devices. The rule also 
amended 14 CFR 121 to specify a date the required flightdeck door was 
to be installed. Thus, the amendment addressed only the ICAO standard 
regarding protection of the flightdeck.
---------------------------------------------------------------------------

    \7\ 67 FR 2118.
---------------------------------------------------------------------------

B. Withdraw or Defer Rule

    Two commenters, Boeing and the Air Transport Association of America 
(ATA), argued that this rulemaking was premature and recommended it be 
withdrawn or deferred for the reasons stated below. Because of the 
nature of the comments, the FAA consulted with

[[Page 63870]]

the Transportation Security Administration (TSA). The following 
discussion represents consensus of the FAA and TSA regarding 
recommendation to withdraw or defer the proposed rule.
1. Coordination With Other Agencies
    Boeing and ATA contend the proposed rule was not properly 
coordinated with agencies that regulate aviation security issues. As 
was noted in the preamble to the NPRM, in October 1999 the FAA formed a 
Design for Security Harmonization Working Group under the auspices of 
ARAC. The task of the new working group was to propose harmonized 
regulations incorporating security measures into airplane design. The 
proposed regulations were to be based on ICAO's Amendment 97 to Annex 
8. At that time, the TSA had not yet been formed. However, its 
predecessor organization within the FAA was a part of ARAC. 
Subsequently, when TSA was established as a separate agency, it 
continued to participate in ARAC.
    After the FAA accepted ARAC's recommendations regarding harmonized 
regulations, we coordinated with TSA throughout the process of drafting 
the NPRM. This close coordination continued during the extensive 
governmental review prior to publication of the NPRM. In fact, Homeland 
Security Presidential Directives (HSPD), the Aviation Transportation 
System Security Plan (ATSS), and the National Strategy for Aviation 
Security all stress that aviation security measures should be fully 
coordinated among the relevant governmental agencies, and coordination 
of this rule was consistent with that approach.
2. Compliance With Certain HSPDs or With the National Strategy for 
Aviation Security
    Boeing and ATA stated that another reason to withdraw or defer the 
rule is it does not comply with Homeland Security Presidential 
Directive 16 (Directive 16) or with the National Strategy for Aviation 
Security.
    This is a more complex issue. Directive 16, issued in June 2006, 
mandates creation of a National Strategy for Aviation Security (the 
Strategy), which in turn is implemented through several security plans. 
The Strategy was issued on March 26, 2007, more than two months after 
publication of the FAA's proposed rule. Subsequently, the FAA and TSA 
reviewed the Strategy and its corresponding plans and concluded that 
this rule does not conflict with those documents. The ATSS notes:
    The FAA also has specific responsibilities and authorities relating 
to safety and security of critical National Airspace System 
infrastructure, as well as responsibility for providing technical 
advice and regulatory certification for aircraft-based attack 
countermeasures.
    The Strategy identifies terrorism and attacks directed at aircraft 
and their occupants as the number one threat to aviation security. This 
rule is consistent with the role of the FAA, as contemplated by the 
ATSS, because it regulates the design and manufacture of certain 
airplane countermeasures to protect the airplane and its occupants.
3. Risk Analysis of the Proposed Approach and Alternatives
    In their comments, ATA and Boeing also recommended the NPRM be 
subject to a formal risk analysis to assess its merits compared to 
alternative aviation security measures. In particular, they urged that 
TSA's Risk Management Analysis Tool (RMAT), which is part of the Risk 
Management Analysis Process (RMAP), be used to assess the proposal. The 
commenters suggested that because the NPRM was not based on a risk 
assessment it may duplicate or needlessly overlap other security 
measures.
    A formal risk analysis tool, such as RMAT, was not available when 
the NPRM was developed. The ARAC supported the measures proposed in the 
NPRM, based on a real threat to aviation, and concluded the proposed 
measures would reduce the risk associated with future attacks. The 
principles that underlie the proposed security measures have their 
origins in work done by the international aviation community dating 
back to the 1980s and are based on the concept of layered security. 
This is an integrated approach which relies on multiple layers of 
security measures, including pre-travel measures, checkpoint measures, 
and aircraft design measures to provide increased protection from 
terrorists and weapons.
    Further, RMAT is a tool which is still under development and 
requires further testing. Given the continuing threat of attacks by 
terrorists, the FAA cannot justify delays in issuing this rule to 
analyze it with a tool that has not yet been validated. New tools for 
risk analysis are developed constantly, and if we wait for the next 
best tool, no regulatory improvements would occur. Based on discussion 
with TSA, we considered whether to use something other than the RMAT to 
address the comments from Boeing and ATA. FAA and TSA concluded that 
this wasn't feasible or necessary. First, there is really no other 
suitable risk model available to address this type of rule. Second, 
risk methodologies utilized by TSA and other agencies whose purview is 
security provided the outside intelligence on which FAA relied 
(beginning with ICAO standards) to determine that the threat of 
terrorist acts was significant and mitigation through airplane design 
was prudent and appropriate. All of the data available, including some 
that is classified, clearly show this rule would provide benefit. 
Regulatory decisions are based on the best information available at the 
time. Therefore, the FAA is amending parts 25 and 121, as proposed, 
with the modifications discussed below.
C. Applicability
    As proposed, Sec.  25.795(a) would apply to new transport category 
airplanes which are required by operating rules to have a flightdeck 
door. Sections 25.795 (b) and (c) would apply to new transport category 
airplanes with a maximum certificated passenger seating capacity of 
more than 60 persons or a maximum certificated takeoff gross weight of 
over 100,000 pounds. Section 121.295 would apply to existing transport 
category airplanes with a passenger seating capacity of more than 60 
persons.
1. Rule Should Apply to All Transport Category Airplanes
    Four commenters, including the Air Line Pilots Association, 
Coalition of Airline Pilots Associations, Passenger-Cargo Security 
Group, and an individual suggested the proposed rule apply to all 
transport category airplanes and not be limited, based on passenger 
capacity or maximum takeoff gross weight. The commenters cited the 
large number of airplanes in the fleet that are below the proposed 
thresholds, sizable passenger and cargo loads carried, threat the 
airplanes would present if commandeered and used as weapons, and the 
desire to apply aviation security measures uniformly.
    As we discussed in the preamble to the NPRM, the intent of the 
proposed rule was to adopt security provisions in design that will be 
effective and at the same time practicable. Limiting the rule to the 
appropriate aircraft was a key task of the Design for Security 
Harmonization Working Group. In fact, as a result of the ARAC 
recommendation and the position of its member states, ICAO amended the 
applicability section of its standards to specify a similar 
applicability. We discussed this matter with the TSA and concluded that 
applying the proposed

[[Page 63871]]

rule to all transport category airplanes would add considerable 
complexity to the design and certification of smaller airplanes without 
measurably improving security.
    In addition, if operating rules require an airplane to have a 
flightdeck door, then--regardless of that airplane's size--the 
requirements for the flightdeck bulkhead will apply. This aspect of the 
proposal most directly addresses use of the airplane as a weapon, which 
was presented as the major concern of the commenters.
    The applicability of the majority of the provisions of Sec.  25.795 
is governed by passenger capacity and gross weight. In the NPRM, we 
stated both criteria are necessary to address airplanes of significant 
size that could carry both passengers and cargo, but be below the 
passenger threshold alone. Clearly, the intent was to capture airplane 
types of a certain size, whether or not they were carrying large 
numbers of passengers.
    In reviewing the language in the rule, we noted the terminology 
used to define passenger capacity limits (``certificated passenger 
seating capacity'') might not be sufficiently clear. The word 
``capacity'' suggests the limit of the airplane's capability. However, 
there could be some confusion whether this applies to each individual 
airplane or to the airplane type. As discussed above, we clearly 
intended to affect the airplane type. Therefore, to clarify the intent, 
the word ``maximum'' has been added to paragraphs (b) and (c) of Sec.  
25.795 as well as Sec.  121.295. This is also consistent with the 
language used to characterize the gross weight limits.
2. Rule Should Also Apply to Airplanes Which Carry Only Cargo
    Several commenters, including the Airline Professionals Association 
(APA), Air Line Pilots Association (ALPA), and Coalition of Airline 
Pilots Associations (CAPA) recommended the proposed requirements should 
also apply to all-cargo airplanes. The commenters specifically cited 
the physical protection of the flightdeck as something that should be 
required on all-cargo airplanes as well as on passenger airplanes. 
Their concern is cargo airplanes frequently operate from airports that 
do not have passenger screening facilities and can be used as weapons 
as effectively as airplanes which carry passengers.
    Existing requirements for reinforced flightdeck doors address all 
transport category airplanes required by operating rules to have a 
flightdeck door. This rule extends those same requirements to the rest 
of the flightdeck bulkhead and other barriers, but does not change the 
applicability of those requirements from a security standpoint. The 
need to reinforce the flightdeck door or, in fact, the need to have a 
flightdeck door depends on restrictions on access to the airplane. We 
have discussed this issue with TSA and concluded that a suitable 
screening program to restrict access to the airplane is as effective as 
physical protection of the flightdeck without a rigorous screening 
program. This subject was discussed in detail in Amendments 121-287 and 
129-37, Flightdeck Security on Large Cargo Airplanes,\8\ and the 
rationale in those rules continues to be applicable.
---------------------------------------------------------------------------

    \8\ 68 FR 42874.
---------------------------------------------------------------------------

3. Rule Should Apply to Existing As Well As New Airplanes
    Several individual commenters recommended the proposed requirements 
be applied to existing airplane models, rather than only new type 
designs.
    As discussed in the NPRM, existing airplanes are already equipped 
with reinforced flightdeck doors and LRBLs that were established 
voluntarily. The remainder of the proposed changes involve design 
changes that are significant for an existing airplane type. The costs 
of making these design changes would be very significant, and the 
benefits would not balance the cost. When developing the proposal, we 
considered various methods of implementation and concluded that 
introduction of these requirements on new type designs would be the 
only approach where benefits outweigh the costs. We have no plan to 
extend any of these requirements to the existing fleet or existing type 
designs. An airplane's certification basis is established in accordance 
with 14 CFR 21, and that will continue to apply in this case. With the 
exception of the change to Sec.  121.295, only airplanes with this 
amendment in their certification basis will be covered by this final 
rule.

D. Secondary Barriers To Protect Flightdeck

    Several commenters, including the CAPA, ALPA, Passenger-Cargo 
Security Group, and several individuals recommended the FAA require 
secondary barriers to provide enhanced security of the flightdeck. ALPA 
cited operational advantages of a secondary barrier when the flightdeck 
door must be opened during flight. The Passenger-Cargo Security Group 
argued that while the reinforced flightdeck door is an effective 
deterrent when it is closed and locked, its effectiveness is 
compromised with the number of times it is opened during flight. 
Therefore, the Group recommended that aircraft have a complementary 
security system and corresponding procedures.
    Adding a requirement for secondary flightdeck barriers to this rule 
would be beyond the scope of the notice, since we did not propose or 
even discuss this issue in the NPRM. Therefore, if we were to conclude 
that secondary barriers should be required, we would have to issue 
another proposal and provide for public comment before adopting such a 
requirement. In any case, we would need the input of TSA and other 
agencies to determine whether security concerns warrant such a 
requirement. Presently, we do not anticipate any rulemaking that will 
require installation of secondary flightdeck barriers.
    Finally, installation of secondary flightdeck barriers is currently 
permitted provided all airworthiness requirements are met and 
associated operational procedures are approved. As mentioned in the 
comment from ALPA, at least one major domestic carrier has developed, 
acquired approval for, and installed secondary barriers on a portion of 
its fleet. In addition, operators have established procedures to permit 
opening of the flightdeck door, and these are working well.

E. Protection of Flightcrew Compartment

    As proposed, Sec.  25.795(a) would specify standards for the design 
of the bulkhead, flightdeck door, and ``any other accessible barrier 
separating the flightcrew compartment from occupied areas.''
1. Use of terms ``Barrier'' and ``Boundary''
    The International Coordinating Council of Aerospace Industries 
Associations (ICCAIA) pointed out that the proposed rule refers to 
``the bulkhead, door, and any other accessible barrier separating the 
flightdeck compartment from occupied areas,'' whereas the proposed 
Advisory Circular uses the term ``boundary.'' In the context of the 
NPRM, we used the term ``barrier'' to indicate the function required. 
In the context of the Advisory Circular, we used the term ``boundary'' 
to help define those items that must serve as barriers. However, we 
agree the distinction is subtle and the term ``boundary'' is more 
general. Therefore, this final rule uses the term ``boundary'' rather 
than ``barrier'' to refer to structures which separate the flightdeck 
from the passenger compartment.

[[Page 63872]]

2. Meaning of Term ``Accessible'' Barrier or Boundary
    Boeing, Bombardier, and the ICCAIA requested clarification of the 
term ``accessible'' barrier (now accessible boundary).
    In the context of resistance to intrusion into the flightdeck, a 
boundary is accessible if it could be exposed to loads from attempts at 
forcible intrusion. If the flightdeck bulkhead is either composed or 
installed forward of other interior structures, such as a galley or 
closet, the contribution of those interior structures to intrusion 
resistance may be included when assessing the acceptability of the 
boundary.
    Boundaries on a multi-deck airplane could include the floor or 
ceiling, although the ceiling might not be accessible if it is high off 
the floor. Generally, physical intrusion through the cabin ceiling 
(from below the flightdeck) would not be feasible because of the 
flightdeck floor structural requirements that must already be met. When 
the cabin is above the flightdeck, the cabin floor is clearly 
accessible. However, it is also likely the existing structural 
requirements for the floor will not permit intrusion through the 
flightdeck ceiling.
    In terms of the ballistic protection provided by a barrier, 
accessibility has a slightly different definition. Barriers are 
accessible, if they are on a hazardous trajectory (as defined in 
proposed AC 25.795-2) from a location accessible to a passenger. 
Interior structures installed aft of a bulkhead would probably not 
provide much ballistic protection. Floors and ceilings on multi-deck 
airplanes will very likely require protection.
    When establishing a hazardous trajectory, an applicant for a new 
type certificate should consider trajectories originating in areas 
beyond the main cabin seating zones if a passenger has access to them. 
Such areas would include any compartment that is not locked. Crew rest 
compartments accessible from the cabin should be evaluated if they are 
not locked or do not have some other means of physically preventing 
unwanted access. This applies even though they are intended only for 
crew use.
3. Placards To Restrict Entry
    An individual commented that placards on the compartment stating 
``crew use only'' would be sufficient. We do not agree. While a placard 
might discourage inadvertent entry by a person, it would not prevent 
entry by a person deliberately trying to gain access. Therefore, an 
area of the cabin, including a compartment not on the main deck, is 
``accessible'' unless there is a physical impediment, such as a lock, 
to entry.

F. Flightdeck Smoke Protection

    As proposed, Sec.  25.795(b)(1) would require that means be 
provided to limit entry of smoke, fumes, and noxious gases from any 
other area of the airplane into the flightdeck.
1. Applicability of Sec. Sec.  25.831 and 25.855
    Boeing commented that the preamble to the NPRM says that Sec.  
25.831 addresses removal of smoke from the flightdeck but does not 
directly address penetration of smoke into the flightdeck, other than 
smoke originating in a cargo compartment. According to the commenter, 
this statement incorrectly implies that Sec.  25.831 contains a 
requirement pertaining to smoke penetration, and it does not.
    We agree that the preamble was misleading on this point. Section 
25.831 addresses removal of smoke from the flightdeck but does not 
address penetration of smoke from cargo compartments. It is Sec.  
25.857 that addresses excluding hazardous quantities of smoke from a 
fire in a cargo compartment from the flightdeck or passenger 
compartment. This matter is clearly addressed in the background section 
of proposed AC 25.795-3, therefore no change is needed to this final 
rule or the Advisory Circular.
2. Clarification of References to Advisory Circular 25-9A
    Boeing and Transport Canada cited several places in the preamble of 
the NPRM where reference to AC 25-9A \9\ could be misinterpreted and 
might not be sufficiently precise.
---------------------------------------------------------------------------

    \9\ Advisory Circular 25-9A, Smoke Detection, Penetration, and 
Evacuation Tests and Related Flight Manual Emergency Procedures; 
January 6, 1994.
---------------------------------------------------------------------------

    We agree that the preamble did not completely characterize the 
criteria provided in AC 25-9A and the relationship of that AC to these 
requirements. Advisory Circular 25-9A covers guidance for testing of 
smoke penetration and removal as well as recommended methods of 
compliance with Sec. Sec.  25.854, 25.855, 25.857, 25.858, and 25.869. 
Clearly, AC 25-9A does not explicitly address the requirements of Sec.  
25.795, since they did not exist at the time the Advisory Circular was 
issued. Therefore, any use of the guidance in AC 25-9A in the context 
of Sec.  25.795 will require adaptation appropriate for the specific 
requirements of this final rule. Nonetheless, some of the recommended 
procedures described in AC 25-9A are directly applicable to procedures 
that could be used to show compliance with Sec.  25.795.
3. Airflow Settings and Dispatch Conditions
    As discussed earlier, the FAA requested in the original tasking 
statement for ARAC that certain comments be addressed by the Design for 
Security Harmonization Working Group. Among them were comments 
regarding protection of the flightdeck from smoke penetration. In 
particular, Boeing and Transport Canada proposed opposite approaches to 
addressing the portions of a flight and the dispatch conditions when 
the capability to resist smoke penetration into the flightdeck should 
be required. Since both organizations were part of the working group, 
we referred the matter to the working group for a recommendation.
    The intent of the requirement is that the airplane be capable of 
limiting smoke penetration into the flightdeck when an explosive or 
incendiary device has been discharged elsewhere on the airplane. We 
recognize that, at any given moment, the airplane may not be making use 
of that capability. However, once the crew becomes aware of the need to 
prevent smoke penetration, they should be able to take action in a 
fairly short time. This is discussed further in proposed AC 25.795-3. 
With regard to dispatch conditions, the conclusion of ARAC is that 
manufacturers should consider the systems that will be permitted to be 
inoperative for dispatch when showing compliance with this requirement. 
This also is noted in the Advisory Circular.
    Transport Canada commented that the method of compliance discussed 
in the preamble and the Advisory Circular-providing small differential 
pressure between the flightdeck and other areas-might not be reliable 
without tests. The commenter concluded that analysis alone would not be 
acceptable to show compliance.
    The FAA agrees that testing is necessary as part of the 
certification process, assuming that the differential pressures are 
very small. As noted in proposed AC 25.795-3, small differential 
pressures are difficult to predict analytically and often cannot be 
measured directly. Once an applicant for a new type certificate 
conducts tests, the FAA may agree that subsequent changes to the design 
could be substantiated by analysis alone if the prior test data remain 
valid. But we agree that in order to establish whether a small 
differential pressure actually exists, a simple test will most likely 
be

[[Page 63873]]

needed. Proposed Advisory Circular 25.795-3 provides one method of 
compliance using testing.
4. Allowable Flightdeck Smoke
    Boeing also proposed language that would state explicitly that the 
rule does not prohibit penetration of any smoke into the flightdeck in 
the immediate aftermath of an event.
    The FAA does not believe that any further clarification is required 
outside this discussion. Both the NPRM and this final rule use the term 
``limit'' rather than ``prevent'' when discussing penetration of smoke 
into the flightdeck. Additionally, proposed AC 25.795-3 clearly states 
that smoke resulting from detonation of an explosive or incendiary 
device ``may initially enter the flightdeck, until the flightcrew 
initiates action to prevent further entry of smoke.''

G. Passenger Cabin Smoke Protection

    As proposed, Sec.  25.795(b)(2) would require that means be 
provided to prevent incapacitation of persons in the passenger cabin 
resulting from smoke, fumes, and noxious gases.
1. Airflow Settings and Dispatch Conditions
    Boeing and Transport Canada addressed the proposed requirements 
pertaining to protection of the passenger cabin from smoke. As with 
protection of the flightdeck from smoke, the comments addressed airflow 
settings and dispatch conditions related to passenger cabin smoke 
protection. These comments were also referred to ARAC for a 
recommendation.
    The purpose of this requirement is that the airplane have the 
capability of coping with a quantity of smoke and other toxic gases in 
the passenger cabin, such that the passengers are not incapacitated. A 
straightforward method of compliance is to change cabin air rapidly 
with outside air. This rapid air change may not be possible in all 
configurations of the environmental control system or all flight 
regimes. In fact, the need to rapidly evacuate smoke from the passenger 
cabin is an emergency procedure for which a change in the ventilation 
rate may be required. Thus, the crew may need to initiate some 
procedures to enable the airplane to meet the required air change rate. 
This is discussed in more depth in proposed AC 25.795-4. No change is 
made to this final rule since the rule simply requires ``means'' to 
protect the passengers.
2. Use of Term ``Fresh Air''
    The NPRM discusses rapid air change using fresh air as one way to 
comply with this requirement under Sec.  25.795(b)(2). Boeing and 
Transport Canada questioned whether using the term ``fresh air'' was 
strictly accurate. Boeing suggested using the term ``outside air'' 
which is more descriptive of our intent.
    The FAA agrees that the word ``fresh'' can have implications about 
air quality and that the quality of outside air is beyond the control 
of the applicant for a new type certificate. Using the term ``outside 
air,'' does not have the same implications about air quality. When 
showing compliance with this requirement by using rapid air changes, 
the key factor is that the air is not re-circulated and originates from 
the outside. Therefore, in the preamble of this final rule, the 
discussion of rapid air change refers to ``outside air.''
    We also noted that the proposed rule language could be interpreted 
as requiring consideration of constant gas concentrations, rather than 
initial gas concentrations. While the preamble discussion of acceptable 
methods of compliance, as well as the characterization of the hazard, 
are clear that the initial concentrations of specific gases must be 
addressed, there is a potential for confusion. To make sure there is no 
misunderstanding, the word ``initial'' is added in paragraph b(2), as 
follows: ``Means must be provided to prevent passenger incapacitation 
in the cabin resulting from smoke, fumes, and noxious gases as 
represented by the initial combined volumetric concentrations of 0.59% 
carbon monoxide and 1.23% carbon dioxide.''

H. Cargo Compartment Fire Suppression

    As proposed, Sec.  25.795(b)(3) would require all components of 
fire suppression systems for cargo compartments be designed to 
withstand certain conditions, unless the systems are either redundant 
and separated in accordance with proposed Sec.  25.795(c)(2) or 
installed remotely from the cargo compartment.
1. Protection From Chemical and Biological Hazards
    The CAPA recommended that the requirements address chemical and 
biological hazards in addition to the effects of an explosive or 
incendiary device.
    While there are no doubt valid security concerns associated with 
these potential hazards, they go beyond the scope and intent of this 
final rule. The rule, as proposed, addressed mitigating effects of 
explosive and incendiary devices from an engineering standpoint. 
Chemical or biological threats introduce entirely different issues and 
potential consequences. Should such threats warrant consideration in 
the airplane design, further rulemaking would be necessary. 
Accordingly, the FAA has made no change to this final rule.
2. Six-Inch Displacement of Components
    Boeing and Bombardier questioned the requirement that all 
components of the cargo compartment's fire suppression system be able 
to withstand ``A 6-inch displacement in any direction from a single 
point force applied anywhere along the distribution system because of 
support structure displacements or adjacent materials displacing 
against the distribution system.'' Bombardier noted that this would 
seem to require a sphere with a diameter of 12-inches of space around 
each point along the distribution system. Boeing stated that certain 
parts of the airplane structure cannot displace 6 inches without 
failure or the distribution system would move with the structure, so 
that there would be no relative displacement.
    These comments were referred to ARAC for consideration, and the 
committee's recommendations form the basis of this discussion. The 6-
inch displacement criterion is not intended to require free space 
surrounding the distribution system. The intent of Sec.  
25.795(b)(3)(iii) is to provide sufficient flexibility that 6-inch 
displacements can be tolerated without failure.
    The space available for displacement will obviously change in the 
event of an explosion. Similarly, the fact that certain structures 
cannot deform 6 inches without failure does not eliminate the potential 
for a relative displacement between the system and its supporting 
structure. Relative displacement can occur due to direct loading or 
secondary contact with adjacent materials or a combination of the two. 
This can occur irrespective of any structural failure and is a 
transient condition that is not readily analyzed. The intent of the 
criterion was to provide a straightforward standard that did not 
require extensive analysis or knowledge of a particular device.
    Nonetheless, the FAA agrees that the proposed criterion could 
require consideration of unrealistic situations and would not 
contribute to safety. Therefore, this final rule addresses those 
situations as follows:
    1. We considered the installation of systems near the fuselage 
contour, for example, in the crown of the airplane

[[Page 63874]]

for a main deck cargo compartment. In this area, a system could not be 
displaced beyond the contour of the fuselage, since the fuselage skin 
itself will not significantly deflect without failure. In those cases, 
the maximum displacement in the direction of the fuselage skin can be 
limited to that which would result in displacement outside the fuselage 
contour.
    2. Similarly, the direction of potential displacement may be 
constrained somewhat since the explosive or incendiary device is 
assumed to be within the cargo compartment. The proposed criterion 
would have resulted in consideration of a displacement in any 
direction. However, considering the direction of loading that would 
result from an explosion within the compartment, there are some 
directions of displacement that are very unlikely.
    Therefore, we have deleted the words ``any direction'' from this 
final rule, giving the applicant for a new type certificate the ability 
to propose how the system could be displaced. We expect the envelope of 
displacement to be no less than a hemispherical shape of a 6-inch 
radius in the direction away from the cargo compartment (except where 
limited by the fuselage contour, as noted above.)
    3. Finally, there may be installations where the potential for 
relative displacement between the distribution system and the structure 
to which it is attached is eliminated. This would not apply to 
attachments involving standoffs or hanging brackets but could apply to 
more substantial structure. An example of such structure is a 
continuous attachment to a floor beam, such that the floor beam would 
have to fail in order to create a relative displacement with the 
distribution system. In that case, the locations where a relative 
displacement could occur would be more limited, and the necessary 
flexibility could be focused into those areas.
    This approach does not address all possible scenarios but is in 
keeping with the intent of the requirement to enhance survivability of 
the system through reasonable and practicable measures. Advisory 
Circular 25.795-5 has also been updated to reflect the change in rule 
language and the discussion above.
3. All-Cargo Airplanes
    The APA, ATA, and CAPA all questioned how the proposed requirement 
would apply to all-cargo airplanes that do not have an active fire 
suppression system installed. They expressed concern that the rule 
might eliminate the current approach to fire protection for all-cargo 
airplanes and require the installation of a fire suppression system. 
Such a system would have to be quite large and contain a large amount 
of extinguishing agent. ATA noted that the cost of certification, 
installation, and maintenance of a fire suppression system on all-cargo 
airplanes is not accounted for in the initial regulatory evaluation.
    This final rule refers to ``an extinguishing agent'' but does not 
require installation of an active fire suppression system for all-cargo 
airplanes, assuming the existing method of fire suppression is 
available. In most cases, fire suppression on all-cargo airplanes 
involves oxygen starvation, rather than application of an extinguishing 
agent. Depressurization at altitude will reduce the available oxygen 
and cause the fire to be suppressed. Since this method should continue 
to be available if an explosive or incendiary device were to detonate, 
an additional fire suppression system would not be necessary.
    This approach is in contrast to that used in Class B cargo 
compartments sometimes used on combination passenger-and-cargo 
airplanes that require a person to enter the compartment to combat the 
fire. After an explosion in the cargo compartment, having a person 
enter the compartment would be neither an acceptable nor a reliable 
method of fire suppression. The fire detection system in the cargo 
compartment of an all-cargo airplane is effectively the same as the 
fire detection system in the cargo compartment of a passenger airplane. 
Therefore, this rule should have little effect on most all-cargo 
airplanes.
4. Eliminate Class B Cargo Compartment on Affected Airplanes
    With respect to Class B cargo compartments, Embraer suggested that 
it would be more clear and direct to simply eliminate them from 
airplanes covered by this proposal. This suggestion has merit; however, 
there is other rulemaking activity that specifically addresses 
standards for Class B cargo compartments. The FAA believes that the 
effects of this final rule and the results of that rulemaking need to 
be considered together. A future Class B cargo compartment might not 
require entry into the compartment to fight a fire. In that case, the 
regulations would have to be amended to permit the use of Class B 
compartments. Therefore, we have not changed the requirements or 
modified the cargo compartment classifications in this final rule.
5. Remove First Sentence of Sec.  25.795(b)(3)
    Embraer also commented that the first sentence of Sec.  
25.795(b)(3) (``An extinguishing agent must be capable of suppressing a 
fire.'') should be removed because it is redundant to requirements 
specified in Sec.  25.857(c)(2). In addition, in proposed AC 25.795-5, 
there is a stated ``assumption'' that ``the system will extinguish the 
fire.''
    We agree; however, the requirements of Sec.  25.795(b) pertain 
specifically to the effects of explosive and incendiary devices which 
are not covered in Sec.  25.857 and, in fact, are addressed only in 
Sec.  25.795(b)(3). Since the assumption in proposed AC 25.795-5 is 
based on the regulatory requirement (Sec.  25.795(b)(3)), lacking the 
benefit of a supporting requirement in the rule, the assumption in the 
Advisory Circular may not be valid. Therefore, we have made no change 
to this final rule.
6. Protecting Pressure Vessels and Certain Other Equipment
    The APA and CAPA questioned the impact criteria for protection of 
pressure vessels and other equipment vulnerable to fragment damage. 
They believe that the fragment velocities are much too low and should 
be on the order of the measured blast wave velocity of an explosive 
itself.
    There may be some confusion as to what the requirements represent 
in terms of the threat. The purpose of the proposed requirement to 
protect against a half inch aluminum sphere traveling at 430 feet per 
second is to account for objects that fragment and are dispersed as a 
result of an explosive or incendiary device. While the fragment 
velocities of the explosive or incendiary device itself may reach very 
high levels, these are not a hazard to the airplane systems. Much of 
the work done to establish these criteria involves sensitive 
information and may not be released to the public. The impact criteria 
were discussed and agreed upon within ARAC, but security considerations 
preclude further detailed discussion in this rule. The FAA has 
considered the issues presented by the commenters and concluded that 
the criteria remain valid.

I. Least Risk Bomb Location

    As proposed, Sec.  25.795(c)(1) would require that an airplane be 
designed with a designated location where a bomb or other explosive 
device could be moved to protect flight-critical structures and systems 
as much as possible from damage in the case of detonation.

[[Page 63875]]

1. Language of Sec.  25.795(c)(1)
    Boeing suggested Sec.  25.795(c)(1) be re-worded to read, ``An 
airplane should be designed with a designated location or other 
mitigation for a bomb * * *.'' Boeing argued that the wording in the 
NPRM goes beyond the intent of the ARAC recommendation and that its own 
suggested wording provides more flexibility.
    Section 25.795(c)(1) is consistent with the ARAC's recommendation. 
Additionally, the FAA believes that use of the word ``should'' is 
inappropriate in this context, as it conveys a recommendation rather 
than a requirement. Finally, the rule is flexible to the extent that a 
``location'' is very general and permits a number of different 
approaches within the airplane. Approaches that do not fall under the 
definition of a ``location'' may be approvable, using the equivalent 
level of safety provisions of Sec.  21.21(b)(1).
2. The Fuel System Is a Critical System
    Transport Canada noted that one of the critical systems that should 
be kept away from the LRBL is the fuel system.
    The FAA agrees that fuel systems are critical systems, as intended 
by this final rule. We will add fuel systems to the discussion in 
proposed AC 25.795-6.

J. Survivability of Systems

    As proposed, Sec.  25.795(c)(2) would require that redundant 
airplane systems necessary for continued safe flight and landing either 
be designed to maximize their ability to survive an event or be 
physically separated by a certain distance, except where that is 
impracticable. The NPRM proposed that redundant systems be separated by 
the diameter of a sphere and specified a formula for calculating that 
diameter.
1. Clarification of System Separation Requirement
    Boeing and Airbus requested clarification on the portions of the 
airplane to which the system separation requirement applies: when must 
an applicant consider the entire spherical volume defined in the 
regulation and when is some lesser volume acceptable. In particular, 
Airbus proposed that the floor and ceiling of the passenger cabin be 
treated like the cargo compartment liner with only half the sphere 
applied to those areas.
    The requirement applies to the entire fuselage, except where 
impracticable and where limited by the boundary of the bulkheads in the 
passenger and cargo compartments. As recommended by ARAC, the 
separation requirement is to be applied in full above the passenger 
ceiling, which is an area often used to route critical systems. 
Significant discussion of the rationale for this requirement in the 
final rule is contained in both the preamble to the NPRM and in 
proposed AC 25.795-7.
2. Purpose of System Separation
    Boeing and Embraer addressed the purpose of system separation. 
Boeing suggested that the final rule explicitly state that the purpose 
of the requirement is to address an explosive or incendiary device. 
Conversely, Embraer suggested that the rule clarify that an explosive 
or incendiary device is only an example of something that system 
separation will help to mitigate.
    While the impetus for the system separation requirement is related 
to security, the requirement will have benefits that extend beyond 
security. We do not believe a revision to regulatory language is 
needed; there is no implication that the requirement is contingent on a 
specific threat. The extent to which the requirement caters to security 
issues is addressed by the ``impracticable'' provisions and the limits 
on application of the sphere beyond the bulkheads in the passenger and 
cargo compartments.
3. Possible Conflict With Other Applicable Regulations
    Boeing and Airbus commented that there are other regulations, such 
as Sec. Sec.  25.729(f) and 25.903(d), that also require system 
separation, and promulgation of Sec.  25.795(c)(2) could create 
conflict.
    This is another subject addressed by the ARAC. The current 
requirements for system protection against high energy rotor failure or 
tire bursts are often met by system separation or shielding. In some 
cases, the traditional approach of system isolation to address a tire 
burst, for example, could result in both parts of a redundant system 
running within the required sphere size for compliance with Sec.  
25.795(c)(2).
    However, after consultation with ARAC, we cannot envision a 
scenario in which compliance with either Sec. Sec.  25.729(f) or 
25.903(d) would preclude compliance with Sec.  25.795(c)(2). 
Nonetheless, if such a situation were to arise, the provision in the 
regulation regarding impracticability would apply, and the applicant 
for a type certificate would show compliance with the regulation 
producing the conflict.
4. Combination of Systems Assumed To Be Inoperative
    Boeing objected to the discussion of the combination of systems 
assumed to be inoperative within the sphere. The NPRM advised a 
manufacturer to consider the effect on continued safe flight and 
landing and whether primary and backup controls for particular systems 
should be separated relative to another system's primary and backup 
controls, essentially so that not only backup controls were available.
    The intent of this discussion was to include an assessment of the 
effects of the system separation approach in addition to the literal 
geometric compliance of the system locations. That is, each system 
taken individually is sufficiently redundant to permit continued safe 
flight and landing, if there is a failure.
    However, assuming a failure renders a combination of systems 
inoperative, with the proper separation, there should be sufficient 
control to permit continued safe flight and landing. Assuming entirely 
redundant systems, the separation alone will address the concern. Even 
if the systems are not 100% redundant, the capabilities of the backup 
system may be such that there is no concern with continued safe flight 
and landing. Nonetheless, the manufacturer should consider the 
ramifications of the inoperative systems and the capability of the 
systems that remain when complying with this requirement.
5. Other Mitigation Measures
    Airbus commented that the rule should make it clear that other 
mitigation measures are required if system separation is impracticable. 
They note that the phrase ``or otherwise designed to maximize their 
survivability'' is intended to address this but believe that the 
wording could be more explicit. They suggested dividing paragraph 
(c)(2) into two paragraphs, to read as follows:
    ``i. Except where impracticable, redundant airplane systems 
necessary for continued safe flight and landing must be physically 
separated, at a minimum, by an amount equal to a sphere * * *. The 
sphere is applied everywhere within the fuselage limited by the forward 
bulkhead, the aft bulkhead, and the liner of the passenger cabin and 
cargo compartment, beyond which only one-half the sphere is applied.
    ``ii. Where compliance with paragraph (i) above is impracticable, 
other design precautions must be taken to maximize the survivability of 
those systems.''

[[Page 63876]]

    We agree with the comment, inasmuch as it makes the requirement 
clearer. Accordingly, the language has been changed in this final rule.
6. Clarification Regarding Reliability and Redundancy
    Airbus also commented that it would like the preamble to state more 
definitively that this requirement does not change the reliability 
requirements of any system or require systems that are not currently 
redundant to become redundant.
    Both of these statements are correct, although there is no change 
needed to the rule language. This final rule adds a requirement to the 
system architecture (i.e., separation) but does not change the 
functional requirements of the systems affected. Proposed AC 25.795-7 
will reflect this intent.
7. Clarification of How To Measure Separation of Systems
    Boeing also asked for a more specific definition of how the 
separation distance was to be measured. Since the affected systems 
themselves have physical dimensions, the separation between them may 
not be a simple distance between points.
    Due to the variety of possibilities and the number of different 
system types, we asked ARAC to address this comment as well. The ARAC 
concluded and we agree that the distance should be determined so that 
the sphere derived from the equation in Sec.  25.795(c)(2) can pass 
between any part of the systems. Proposed AC 25.795-7 has been revised 
to reflect this same approach.

K. Clarification of Sec.  25.795(c)(3)

    As proposed, Sec.  25.795(c)(3) would require that certain parts of 
the cabin be designed to make it more difficult to hide weapons, 
explosives, or other objects and easier to search for them. The 
specific parts of the cabin are the areas above the overhead bins, the 
toilets, and the life preservers or the areas where they are stored.
    The ICCAIA, Bombardier, and Airbus all requested clarification on 
the degree to which the area above stowage compartments must prevent 
concealment of an object. In particular, they asked about the size of 
the object to be considered and how the acceptability of the design 
would be assessed. This is a subject that had initially been discussed 
in ARAC's Design for Security Harmonization Working Group but was not 
resolved. However, because of the evident need for a standard, we 
referred this comment to the working group for its recommendation.
    The working group reached consensus on an approach for the interior 
design that should simplify the compliance findings. Although Boeing 
provided a dissenting opinion, the Transport Airplane and Engine Issues 
Group concurred with the working group and forwarded the recommendation 
to the FAA. In summary, the working group recommended an approach using 
objects of varying shapes that have a volume of 20 cubic inches or 
larger. A designer that elects to use this approach would have a 
straightforward way of showing compliance. This method is described 
more fully in AC 25.795-8. Nevertheless, since the commenters requested 
additional clarification, we have decided to add a provision defining a 
method of compliance that will always be found compliant, for designs 
that prevent concealment of 20 cubic inch objects. The rule also 
permits other methods acceptable to the Administrator. This would 
include other approaches using standard objects, as well as design 
features to eliminate the space above the overhead bins. Designs that 
prevent concealment of objects smaller than 20 cubic inches would, of 
course, also be acceptable.
    The requirements of Sec.  25.795(c)(3) are intended to facilitate 
searching and are a way to improve the design to that end. The actual 
search process and the types of things for which a search is conducted 
are not changed by this requirement. By improving the design and making 
it easier to search, the search is more effective and more efficient. 
This requirement should not affect operators when an airplane is 
searched, other than making the search more effective and efficient as 
noted above. It is simply a way to gauge the effectiveness of the 
design in improving the searchability of the airplane.
    Qantas Airways and the ATA commented that improved interior design 
to facilitate searches was highly desirable and that any efforts in 
this area need to be coordinated with the Transportation Security 
Administration. Qantas commented that the regulatory requirements (that 
involve the design) imposed on the operator by TSA should be 
requirements on the airframe manufacturer as well.
    We agree that good coordination with TSA is needed and have 
coordinated this rulemaking extensively with TSA. In terms of 
regulatory compliance, regulations are specific in their applicability. 
To the extent that these requirements apply only to persons subject to 
the rule, good cooperation between the regulators, manufacturers, and 
operators is the key to impr