Revisions to Digital Flight Data Recorder Regulations for Boeing 737 Airplanes and for Part 125 Operators, 52382-52401 [06-7406]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 71, Number 171 (Tuesday, September 5, 2006)]
[Proposed Rules]
[Pages 52382-52401]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-7406]



[[Page 52381]]

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

Part II





Department of Transportation





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



Federal Aviation Administration



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



14 CFR Parts 91, 121, and 125



 Revisions to Digital Flight Data Recorder Regulations for Boeing 737 
Airplanes and for Part 125 Operators; Proposed Rule

Federal Register / Vol. 71, No. 171 / Tuesday, September 5, 2006 / 
Proposed Rules

[[Page 52382]]


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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 91, 121, and 125

[Docket No.: FAA-1999-6482; Notice No. 06-12]
RIN 2120-AG87


Revisions to Digital Flight Data Recorder Regulations for Boeing 
737 Airplanes and for Part 125 Operators

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental Notice of Proposed Rulemaking (SNPRM).

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

SUMMARY: The FAA is revising a previous proposal to increase the number 
of digital flight data recorder (DFDR) parameters required for all 
Boeing 737 series airplanes. Based on safety recommendations from the 
National Transportation Safety Board (NTSB) following the 
investigations of two accidents and other incidents involving 737s, the 
FAA proposed the addition of flight recorder equipment to monitor the 
rudder system on 737s. Since that time, the FAA has mandated 
significant changes to the rudder system on these airplanes. 
Accordingly, this new proposed rule would apply to a different set of 
airplanes than originally anticipated. We are requesting comment on 
this change in applicability and are requesting updated economic 
information regarding installation of the proposed monitoring 
equipment. The original proposed rule also sought to amend the flight 
data recorder (FDR) requirements of part 125 that would affect all 
airplanes operated under that part or under deviation from that part; 
we have included that same proposal in this SNPRM.

DATES: Send your comments on or before December 4, 2006.

ADDRESSES: You may send comments identified by Docket Number FAA-1999-
6482 using any of the following methods:
     DOT Docket Web site: Go to https://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to https://
www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility; U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590-0001.
     Fax: 1-202-493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For more information on the rulemaking process, see the 
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
https://dms.dot.gov, including any personal information you provide. For 
more information, see the Privacy Act discussion in the SUPPLEMENTARY 
INFORMATION section of this document.
    Docket: To read background documents or comments received, go to 
https://dms.dot.gov at any time or to Room PL-401 on the plaza level of 
the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical issues: Timothy W. 
Shaver, Avionics Systems Branch, Aircraft Certification Service, AIR-
130, Federal Aviation Administration, 800 Independence Avenue, SW., 
Washington, DC 20591; telephone (202) 385-4686; facsimile (202) 385-
4651; e-mail tim.shaver@faa.gov. For legal issues: Karen L. Petronis, 
Senior Attorney, Regulations Division, AGC-200, Office of the Chief 
Counsel, Federal Aviation Administration, 800 Independence Ave., SW., 
Washington, DC 20591; telephone (202) 267-3073; facsimile (202) 267-
7971; e-mail: karen.petronis@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. We also 
invite comments relating to the economic, environmental, energy, or 
federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, 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 this proposed rulemaking. 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 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. You may also review the docket using the 
Internet at the Web address in the ADDRESSES section.
    Privacy Act: Using the search function of our docket Web site, 
anyone can find and read the comments received into any of our dockets, 
including the name of the individual sending the comment (or signing 
the comment on behalf of an association, business, labor union, etc.). 
You may review DOT's complete Privacy Act Statement in the Federal 
Register published on April 11, 2000 (65 FR 19477-78) or you may visit 
https://dms.dot.gov.
    Before acting on this proposal, 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 this proposal in light of the comments 
we receive.
    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 to you.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be 
proprietary or confidential business information. Send or deliver this 
information directly to the person identified in the FOR FURTHER 
INFORMATION CONTACT section of this document. You must mark the 
information that you consider proprietary or confidential. If you send 
the information on a disk or CD-ROM, mark the outside of the disk or 
CD-ROM and also identify electronically within the disk or CD-ROM the 
specific information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information 
filed with a comment, we do not place it in the docket. We hold it in a 
separate file to which the public does not have access, and place a 
note in the docket that we have received it. If we receive a request to 
examine or copy this information, we treat it as any other request 
under the Freedom of Information Act (5 U.S.C. 552). We process such a 
request under the DOT procedures found in 49 CFR part 7.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Department of Transportation's electronic Docket 
Management System (DMS) Web page (https://dms.dot.gov/search);

[[Page 52383]]

    (2) Visiting the FAA's Regulations and Polices Web page at https://
www.faa.gov/regulations_policies/; or
    (3) Accessing the Government Printing Office's Web page at https://
www.gpoaccess.gov/fr/.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, notice number or amendment number 
of this rulemaking.
    Anyone is able to search the electronic form of all comments 
received into any of our dockets by the name of the individual 
submitting the comment (or signing the comment, if submitted on behalf 
of an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act statement in the Federal Register published on 
April 11, 2000 (Volume 65, Number 70; Pages 19477-78) or you may visit 
https://dms.dot.gov.

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SBREFA) of 
1996 requires FAA to comply with small entity requests for information 
or advice about compliance with statutes and regulations within its 
jurisdiction. If you are a small entity and you have a question 
regarding this document, you may contact your local FAA official, or 
the person listed under FOR FURTHER INFORMATION CONTACT. You can find 
out more about SBREFA on the Internet at https://www.faa.gov/avr/arm/
sbrefa.htm, or by e-mailing us at -AWA-SBREFA@faa.gov. https://
www.faa.gov/regulations_policies/rulemaking/sbre_act/.

Authority for This Rulemaking

    The FAA's authority to issue rules regarding 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. Under that section, 
the FAA is charged with prescribing regulations providing minimum 
standards for other practices, methods and procedures necessary for 
safety in air commerce. This regulation is within the scope of that 
authority since flight data recorders are the only means available to 
account for aircraft movement and flight crew actions critical to 
finding the probable cause of incidents or accidents, including data 
that could prevent future incidents or accidents.

I. Background

A. Statement of the Problem

    Two aviation accidents in the United States involving Boeing 737 
series airplanes (737s) appear to have been caused by a rudder hardover 
with resultant roll and sudden descent: United Airlines flight 585, 
near Colorado Springs, Colorado, on March 3, 1991, and USAir flight 
427, near Aliquippa, Pennsylvania, on September 8, 1994. Following 
lengthy investigations, the NTSB determined that the rudder on 737s may 
experience sudden uncommanded movement, or movement opposite the 
pilot's input, which may cause the airplane to roll suddenly. Other 
incidents of suspected uncommanded rudder movement have been reported, 
including a 1996 incident involving Eastwind Airlines (Eastwind) flight 
517, a 737-2H5, and five incidents in 1999 involving U.S.-registered 
airplanes.
    The 737s involved in the United Airlines and USAir accidents, and 
those in the more recent incidents, were equipped with the flight data 
recorders required by the regulations then in effect. However, these 
airplanes were not required to record, nor were they equipped to 
provide, information about the airplane's movement about its three axes 
or the position of flight control surfaces immediately preceding the 
accident or incident. While the FAA has undertaken a series of measures 
designed to address the suspected rudder problems, our efforts have 
been limited by a lack of data that focused on the control and movement 
of the components of the 737 rudder system. Without more data, neither 
the FAA nor the NTSB can definitively identify the causes of suspected 
uncommanded rudder events.

B. FAA Actions

    Following piloted computer simulations of the USAir accident and 
reports of malfunctions in the yaw damper system of 737s, the FAA 
mandated design changes to the rudder system of 737s. First, the FAA 
issued Airworthiness Directive (AD) 97-14-03 (62 FR 34623, June 27, 
1997), which requires installation of a newly designed rudder-limiting 
device and a newly designed yaw damper system, in an effort to address 
possible rudder hardover situations and uncommanded yaw damper 
movements. Second, in response to the possibility of a secondary slide 
jam and rudder reversal, the FAA issued AD 97-14-04 (62 FR 35068, June 
30, 1997). That AD requires operators to install a new vernier control 
rod bolt and a new main rudder power control unit (PCU) servo valve in 
each airplane.

C. Safety Recommendations: 1995-1997

    Between 1995 and 1997, while investigating the USAir accident, the 
NTSB issued 20 safety recommendations dealing with the 737; three of 
those (A-95-25, A-95-26, and A-95-27) dealt specifically with upgrades 
to the FDR for all 737s. The NTSB stated that if either the United 
Airlines or the USAir 737 had recorded data on the flight control 
surface positions, flight control inputs, and lateral acceleration, the 
NTSB would have been able to identify quickly any abnormal control 
surface movements and configuration changes or autopilot status changes 
that may have been involved in the loss of control.
    At the time it made its recommendations, the NTSB recognized that 
the 737 had flown over 92 million hours since its initial certification 
in December 1967, and that the airplane's accident rate is comparable 
to that of other airplanes of a similar type. Nonetheless, the Board 
concluded that the design changes made to the rudder system in 
accordance with the issued ADs did not eliminate the possibility of 
other potential failure modes and malfunctions.

D. FAA Response: 1997 Regulations

    In response to these safety recommendations, the FAA published 
revisions to the DFDR requirements for all airplanes (Revisions to 
Digital Flight Data Recorder Rules; Final Rule (62 FR 38362, July 17, 
1997)). The revised DFDR regulations prescribe the 88 parameters that 
must be recorded on DFDRs, with the exact number of parameters required 
to be recorded determined by the date of airplane manufacture. The 
number of parameters that must be recorded range from 18 for a 
transport category airplane manufactured on or before October 11, 1991, 
to 88 for airplanes manufactured after August 19, 2002.

E. NTSB's 1999 Findings and Safety Recommendations

    On March 24, 1999, the NTSB issued the final report of its 
investigation into the crash of USAir flight 427. The NTSB determined 
that the probable cause of the accident was a loss of control resulting 
from the movement of the rudder surface position to its blowdown limit. 
Further, the NTSB stated that


[[Page 52384]]


    ``* * * the rudder surface most likely deflected in a direction 
opposite to that commanded by the pilots as a result of a jam of the 
main rudder PCU servo valve secondary slide to the servo valve 
housing offset from its neutral position and overtravel of the 
primary slide.''

    In its March 1999 report, the NTSB concluded that the 1997 
regulations for upgrading DFDRs are inadequate for existing 737s, 
because they do not require specific flight control information to be 
recorded. Because several 737 rudder-related events have been 
associated with the yaw damper system (which moves the rudder 
independent of flightcrew input), the NTSB concluded that it is 
important that yaw damper status (parameter 89), yaw damper command 
(parameter 90), standby rudder status (parameter 91), and control 
wheel, control column, and rudder pedal forces (parameter 88) be 
recorded on all 737s. The NTSB also pointed out that, for optimal 
documentation, the indicated parameters need to be sampled more 
frequently than is required currently. The NTSB stated that by 
recording the yaw damper's operation and the resultant rudder surface 
movements, a yaw damper event could be distinguished quickly from a 
flightcrew input or a rudder anomaly. The NTSB considers this 
information critical to investigating 737 incidents or accidents. The 
NTSB stated that if pilot flight control input forces had been recorded 
on the United Airlines, USAir, or Eastwind FDRs, the NTSB 
investigations would have been resolved more quickly and actions taken 
to prevent similar events would have been hastened.
    On April 16, 1999, the NTSB submitted the following recommendations 
to the FAA regarding recording additional parameters on 737 DFDRs:
    Recommendation No. A-99-28. Require that all 737s operated under 
part 121 or part 125 that currently have a FDAU be equipped, by July 
31, 2000, with a flight data recorder system that records, at a 
minimum, the parameters required by the 1997 DFDR regulations 
applicable to that airplane, plus the following parameters: Pitch trim, 
trailing edge flaps, leading edge flaps, thrust reverser position (each 
engine), yaw damper command, yaw damper status, standby rudder status, 
and control wheel, control column, and rudder pedal forces. Yaw damper 
command, yaw damper status, and control wheel, control column, and 
rudder pedal forces should be sampled at a minimum rate of twice per 
second.
    Recommendation No. A-99-29. Require that all 737s operated under 
part 121 or part 125 that are not equipped with a FDAU be equipped, at 
the earliest time practicable, but no later than August 1, 2001, with a 
flight data recorder system that records, at a minimum, the same 
parameters noted in safety recommendation No. A-99-28.
    The NTSB also noted in its final report on the USAir accident that 
737 flightcrews continue to report anomalous rudder behavior and that 
the NTSB considers it possible that another catastrophic event related 
to 737 rudder upset could occur.

F. FAA Response: Notice No. 99-19

    The FAA agreed with the intent of NTSB Safety Recommendation Nos. 
A-99-28 and A-99-29 and the NTSB's concerns regarding continuing 
reports of rudder-related incidents on 737s. On November 9, 1999, the 
FAA issued Notice No. 99-19 (64 FR 63140, November 18, 1999), which 
proposed that all 737s be required to record the parameters listed in 
Sec.  121.344(a)(1) through (a)(22), (a)(88), plus three new 
parameters, designated as (a)(89) through (a)(91). The new parameters 
are yaw damper status, yaw damper command, and standby rudder status. 
In addition, the FAA proposed increasing the required sampling rate for 
the control forces listed in current paragraph (a)(88) for 737s. The 
FAA proposed that all 737s equipped with a FDAU of any type as of July 
16, 1996, or manufactured after July 16, 1996, comply by August 18, 
2000. For all 737s not equipped with a FDAU of any type as of July 16, 
1996, the FAA proposed a compliance date of August 20, 2001. The FAA 
noted that if it received sufficient data to support an extension, the 
compliance period for airplanes retrofitted to include FDAUs between 
July 16, 1996, and November 18, 1999, would be extended to August 19, 
2002.
    The FAA proposed corresponding changes to part 125 for 737s 
operated under that part. In addition, the FAA proposed that no 
deviation authority from the FDR requirements of part 125 would be 
granted for any model airplane, and that any previously issued 
deviation from the DFDR requirements of part 125 would no longer be 
valid. The FAA also proposed that Sec.  91.609 be amended to reflect 
that all airplanes operating under part 91 under deviation authority 
from part 125 must comply with the DFDR requirements in part 125, 
notwithstanding such deviation authority.

II. Continuing Need for This Rulemaking

    The original NPRM, issued by the FAA in 1999, proposed that in 
addition to other applicable requirements, all 737 model airplanes must 
record certain additional parameters of flight data, including those 
specifically designed to monitor rudder system components. The FAA 
added that it planned on issuing the final rule with an immediate 
effective date to address the unresolved issues with the airplane as 
soon as possible.
    In January 2001, Boeing submitted a letter to the docket requesting 
that the FAA delay the release of any final rule. The request was based 
on Boeing's 737 Rudder System Enhancement Program (RSEP), which itself 
was based on an NTSB recommendation to develop a ``reliably redundant 
rudder system'' for the 737. Boeing stated that the RSEP changes will 
make the 737 rudder system functionally equivalent to the 3-actuator 
system found on its 757 and 767 model airplanes.
    Boeing's letter states that on January 16, 2001, it presented a 
detailed description of its 737 RSEP changes to the NTSB. While noting 
that the proposed rule would be applicable to the original rudder 
system, not the one being developed under the RSEP, it attempted to 
minimize the value of a final rule that applied only to airplanes with 
the older system installed. Boeing also questioned whether it would 
still be appropriate to treat the 737 different than other airplanes 
once the rudder system was modified.
    While the redesigned rudder control system meets the latest FAA 
system requirements, it remains a system unique to the 737 model 
airplane. In Boeing 757/767/777 model airplanes, the rudder control 
system has three separate actuators in separate power control units 
(PCU) that are always powered. The original design of the 737 rudder 
control system had a single input into a valve that controlled two 
installed actuators in the PCU. In the redesigned 737 system, there are 
three actuators, but they are housed in two PCUs rather than the three 
present in the other Boeing model airplanes. The main PCU has two 
actuators, each with its own valve that accepts input. The third 
actuator is in a standby PCU that is not normally powered unless the 
main PCU fails. Thus, the 737 rudder control system effectively still 
has only two actuators during normal flight operations, and a single 
actuator when the main PCU is inoperative.
    Several events have occurred since the NPRM was issued in 1999, 
including Boeing's RSEP. One of the recommendations issued by the NTSB 
included the formation of an engineering test and evaluation board 
(ETEB) to conduct a failure analysis of

[[Page 52385]]

the rudder actuation control system of the 737. The 737 ETEB was formed 
in May 1999 and issued its final report in July 2000.
    Among the key findings of the 737 ETEB are the following:
    (1) The 737 rudder control system is susceptible to a number of 
failures and jams. These failures and jams can affect the operation of 
the rudder power control units and can result in uncommanded rudder 
motion.
    (2) A number of failures and jams of the 737 rudder control system 
were detected in configurations on which the FAA later issued 
corrective action under one or more Airworthiness Directives (ADs). 
More than two dozen of these failures and jams (alone or in 
combination) have what are considered catastrophic failure effects.
    (3) Even when 737s were in compliance with the ADs issued at the 
time, rudder control system failures and jams were still present.
    (4) Most of the failure modes were discernable on both the older 
(classic) models and the newer (next generation) models of the 737.
    (5) There were no catastrophic failure modes identified at cruise 
speed and altitude. One change to the hydraulic pressure system 
mandated by AD reduced the time an airplane was exposed to catastrophic 
failure modes, but exposure was not eliminated during takeoffs and 
landings.
    Among its recommended long-term actions, the ETEB recommended that 
the 737 rudder system be modified to ensure that no single failure or 
single jam of the rudder control system would cause an uncommanded 
rudder motion that has catastrophic results.
    The NTSB did not withdraw or change its recommendation regarding 
further monitoring of the rudder system on 737s, and indicated in a 
February 2001 letter to the FAA that it had not changed its position 
regarding the need for installation of the new FDR equipment ``at the 
earliest possible opportunity regardless of any rudder system 
modification.''
    In November 2001, the FAA published a proposed AD that would 
require the installation of a new rudder control system (and 
accompanying changes to nearby systems) (66 FR 56783, November 13, 
2001). The FAA determined that the inherent failure modes in the 737 
rudder system, verified by the ETEB, result in a design system 
architecture that is unsafe. The FAA also determined that the rudder 
system design architecture led to a need for non-normal operational 
procedures, which had also been implemented by AD. The FAA concluded 
that the combination of the inherent failure modes and the non-normal 
operational procedures, considered together, present an unsafe 
condition that warranted the incorporation of a newly designed rudder 
control system.
    The final rule AD was published on October 7, 2002 (67 FR 62341), 
with an effective date of November 12, 2002, and gives all operators of 
737 model airplanes 6 years to install a new rudder control system.
    Boeing has been installing the newly designed rudder control system 
on 737 model airplanes manufactured since January 2003. Boeing is also 
installing the additional sensors that were proposed in the NPRM on 
these newly manufactured 737s, and those parameters are being recorded.
    When we began drafting a final rule, we realized that the 737 fleet 
that would be affected by the proposed rule--those airplanes with the 
original rudder system--had already begun to shrink in number. The 
promulgation of several Airworthiness Directives means that by the 2008 
compliance date for those ADs, no 737 aircraft left in the U.S. fleet 
would have the old rudder system. Therefore, we no longer find it 
appropriate to require the installation of flight recorder equipment to 
monitor those parts of the aircraft which became life-limited by these 
ADs and will be eliminated by 2008.
    This SNPRM attempts to address the changes in circumstances 
introduced by the RSEP, the findings by the ETEB, and the ADs issued by 
the FAA by revising the fleet of airplanes affected by the proposed 
rule, and by changing the proposed compliance time to coincide with the 
modifications required by the ADs.
    The FAA does not have convincing evidence that the redesigned 
rudder control system obviates the need for the additional flight 
recorder parameters. The newly designed rudder system is unique in that 
the third actuator is only activated upon the failure of the main PCU, 
at which point the two main actuators are no longer performing. Thus, 
the FAA has tentatively concluded that the information that would be 
gathered by the addition of the proposed parameters could provide 
meaningful information in the event of a rudder control failure. While 
the ETEB conducted considerable testing of the 737 aircraft and its 
rudder system, those tests cannot duplicate the actual flight 
experience of either the original or the new rudder system as it would 
be recorded using the parameters proposed. The only way to get this 
data is by installation of equipment that will record the movement of 
the rudder surface and the companion actions of the yaw dampers. The 
ETEB did not have this information because the equipment to record it 
was not mandatory. Since the additional parameters have yet to be 
installed, investigators of an accident or incident remain similarly 
limited today.
    Boeing has indicated that there have been no reports of rudder 
hardover incidents on 737s with the redesigned rudder system. However, 
since the system has only been installed as original equipment on 
airplanes since 2003, and since compliance with the retrofit is not 
required until 2008, only limited historical data on the function and 
reliability of this redesigned system is available.
    Additionally, as discussed above, the redesigned rudder system does 
not actively power three actuators. Rather, the third actuator only 
powers up in the event of a power failure to the two primary actuators. 
Thus, while the new design incorporates three actuators, similar to the 
design of Boeing's 757/767/777 model airplanes, a functional difference 
remains between the new 737 rudder system and that installed on other 
Boeing airplanes.
    We note that the rudder control system enhancement can be split 
into three separate tasks and are not normally accomplished at once. 
The first two changes can be accomplished with the old rudder control 
system still in place. As of August 2004, Boeing had shipped 2,957 kits 
needed for the first part of the installation, but only 728 kits for 
the third part. The FAA assumes these numbers have gone up; however, 
since there is no reporting requirement for compliance with the AD, we 
have no way of knowing how many new components or complete rudder 
control systems have been installed. However, the FAA understands that 
the wiring kit provided by Boeing for the first part of the redesigned 
rudder system includes the wiring required for the proposed additional 
sensors, making the installation of the parameters less burdensome than 
originally anticipated. Compliance with this rule, if adopted, would 
require the installation of the sensors and their connection to the 
DFDR system. These circumstances argue for either the issuance of this 
rule (to take advantage of the work yet to be accomplished on the 
majority of the 737 fleet) or withdrawal, as soon as possible.
    We continue to believe that unless the proposed additional flight 
recorder sensors are installed and the function of the new system 
components are monitored, there will never be any means to eliminate 
the rudder system as a possible cause of any future incident

[[Page 52386]]

or accident, or to identify the particular component or action as a 
source of the problem if the rudder control system is involved. These 
are the circumstances that spurred the original NTSB recommendations on 
the 737, but we are cognizant of the significant changes in 
circumstances that have occurred in the last five years, including the 
mandated changes to the original rudder system, and the decline in 
reported incidence of rudder hardover events.
    We are also aware that we now need new information on the costs and 
benefits of requiring these enhancements on a fleet of aircraft that 
did not exist when we originally proposed the rule, those with the new 
rudder system installed.
    The FAA originally evaluated the cost data associated with this 
SNPRM nearly five years ago, shortly after the close of the comment 
period for the NPRM. Since then, some 737s may have been retrofitted 
with the new rudder, and may be partially equipped to record the 
additional flight data parameters. Further, with the introduction of 
the new Boeing 737 rudder, there is a new class of airplane that will 
incur retrofitting costs that may be different from those costs 
reported by the industry and used in the Supplemental Preliminary 
Regulatory Evaluation (Supplemental PRE) that accompanies this 
rulemaking document. Because the FAA does not have the data necessary 
to evaluate the impact of, and need for, a rule requiring the 
additional parameters for those 737s equipped with the new rudder 
control system, the agency requests more current information for the 
following specific questions as well as any additional data that the 
public believes needs to be incorporated into the economic analysis.
    1. How many 737s are in your fleet?
    2. How many 737s do not record the flight parameters that we are 
proposing be recorded? How many 737s currently record these parameters?
    3. How many 737s have been retrofitted with the new Boeing rudder? 
How many of those airplanes do not record the flight data parameters 
that we propose to be recorded?
    4. How many 737s are expected to be retrofitted with the new Boeing 
rudder in each of the years 2006, 2007, and 2008?
    5. How many 737s are expected to be retired in each of the years 
2006, 2007, and 2008?
    6. For those 737s that have already been retrofitted under the AD 
but do not record the additional flight data parameters, how much would 
it cost to install the equipment to record the additional flight data 
parameters? How many days would it take to install the equipment to 
record those additional flight data parameters on those airplanes if 
the work were done: during a major maintenance session; an overnight 
maintenance session?
    7. Are the assumptions and estimates made in Table 1 of this notice 
and the accompanying Supplemental PRE, and throughout that report, 
accurate? If you are able to provide more current data, please submit 
it.
    8. Please provide an update on the status of the various design 
changes that would still need to be accomplished to provide the 
information necessary to install the proposed flight recorder 
parameters on the fleet expected to be retrofitted with the new rudder 
design.
    We are issuing this SNPRM to gather information on the need for 
flight recorder parameters that monitor the new rudder system. This 
proposal represents a shift in the scope of the rule. When the DFDR 
enhancements were proposed, work was still in progress in diagnosing 
the functions and perceived weaknesses of the original rudder system. 
We have modified the original proposed regulatory text to require that 
the flight recorder parameters proposed in 1999 be installed concurrent 
with the new rudder system; we have redrafted the rule to state that 
compliance would be required no later than November 12, 2008, the date 
that compliance is required with the Airworthiness Directives mandating 
the installation of the redesigned rudder system. We have made other 
changes to the proposed regulatory text based on comments to the NPRM. 
These changes, which are explained later in the document, will not be 
revisited. Accordingly, we request interested parties to direct their 
attention to our requests for data, the need for additional parameters 
for the redesigned 737 rudder control system, and the proposed November 
2008 compliance date.
    In summary, the FAA finds this supplemental proposal necessary in 
order to update the status of the number and configuration of 737s in 
the current fleet. Since we do not track operator compliance with ADs, 
the information requested here will tell us how many airplanes have 
been retrofitted with the new rudder system and the estimated costs for 
installing the DFDR parameters if the new rudder system has already 
been installed. We expect to receive information on the number of 
retirements expected, as well as the number of aircraft that are 
already in compliance because they are new or because the proposed DFDR 
rudder parameters may have been installed voluntarily.

III. Summary of Comments

    The FAA received 17 comments on the proposed rule. Of the 17 
comments, the Air Transport Association of America, Inc. (ATA), 
submitted three separate comments; one of the ATA submissions included 
seven comments from member airlines. Only one commenter, the Air Line 
Pilots Association (ALPA), supports the proposed rule as published. 
Specifically, ALPA agreed that a potentially unsafe condition has been 
identified and concurs with the proposed amendments. The other 
commenters generally supported the intent of the proposed rule; 
however, these commenters expressed concern about:
    (1) The time frame for compliance proposed in the Notice of 
Proposed Rulemaking (NPRM),
    (2) the availability of installation instructions,
    (3) the unavailability of parts, and
    (4) the probability of considerable airplane out-of-service time.
    The amount of time that has elapsed since comment was invited, and 
the events that have occurred since comment was invited, has caused 
most of the comments to become outdated. The proposed compliance times 
are no longer applicable, nor are the costs that were applied to them. 
Accordingly, we are not including a discussion of comments concerning 
compliance time, parts availability, or out of service time since these 
issues no longer exist under current circumstances.

Comments on Specific Proposed Requirements

    The following disposition of comments addresses those comments that 
were not overtaken by intervening events and actions. Some of the 
questions and information submitted with them remain relevant to the 
actions contemplated under this modified proposal.
    Boeing stated that it typically does not develop or commit to 
design changes until the release of a final rule. However, because of 
the proposed short time frame for compliance, Boeing had already 
implemented production design changes in an attempt to accommodate the 
expected compliance schedule. Boeing noted that a typical design change 
of this magnitude would require a minimum of 18 months to allow time to 
develop the design and to work with parts suppliers, operators, and the 
FAA.

[[Page 52387]]

A. Compliance Issues for Rudder Pedal Forces

    Proposal: The FAA stated in Notice No. 99-19 that it had received 
inquiries from the NTSB and Boeing concerning an acceptable means of 
recording the rudder pedal control input forces required by paragraph 
(a)(88) of Sec.  121.344; the requirement was added in the 1997 
amendment to the DFDR regulations.
    To meet the 1997 regulations, Boeing developed a rudder pedal force 
transducer that is placed ``midstream'' in the rudder control system. 
The transducer is designed to identify whether the input was coming 
from the cockpit or from the rudder assembly.
    The NTSB indicated informally that it would prefer a system that 
measures the rudder input force at the individual rudder pedals. This 
would require the addition of four transducers (one on each rudder 
pedal) rather than the single one designed by Boeing. The FAA noted 
that the NTSB believes that only the installation of four rudder pedal 
force sensors would meet the intent of its April 16, 1999 
recommendation to record rudder input force.
    The FAA acknowledged the difference between the data acquired using 
Boeing's already approved single transducer system and the NTSB's 
suggested four-pedal sensor retrofit. The FAA requested comment on the 
necessity and feasibility of instrumenting all four rudder pedals on 
737s with force sensors as a means of complying with paragraph (a)(88). 
The FAA also requested comment on whether Boeing's single force 
transducer should remain an accepted means of compliance with parameter 
88 for all 737s that do not have the transducer installed or had not 
yet otherwise complied with paragraph (a)(88). In addition, the FAA 
requested cost data for the four-pedal retrofit to determine whether 
the incremental increase in benefits that would be provided by that 
configuration would be offset by the additional time and costs involved 
if such a requirement were mandated.
    Comments: The FAA received two comments on recording rudder control 
inputs, one from the NTSB and one from Boeing.
    The NTSB stated that the rudder pedal force exerted by each 
crewmember is critical to its understanding the loss of control 
problems experienced in the 737. The NTSB added that in its 
investigation of a 1999 rudder incident involving Metrojet, not knowing 
the amount of rudder pedal force exerted has made it impossible to 
separate pilot actions from (possible) rudder system anomalies. The 
Board argued that a single sensor placed midstream in the rudder 
control system, as introduced by Boeing, would not identify whether the 
flightcrew inputs are in opposition to each other or whether the nose 
wheel steering (NWS) or some other system anomaly forward of the sensor 
causes the inputs. In addition, any jams in the controls between the 
pedals and the sensor may go undetected, because the amount of force 
exerted by the flightcrew would not be registered by the sensor. The 
NTSB stated that, if the upgrade required only a single force sensor in 
the rudder system, the possibility would remain that the information 
would not be sufficient to identify some future flight control problems 
even after the proposed retrofit.
    Boeing commented that neither the existing rule nor the proposed 
rule includes specific requirements that support a change to the 
current design to measure individual rudder pedal force. Boeing stated 
that the 1997 rule contained no requirement to measure any disagreement 
between pilot inputs. According to Boeing, the NTSB recommendations and 
the proposed rule suggested that the only issue is the ability to 
quickly distinguish a yaw damper event from a flightcrew input or a 
rudder anomaly. Boeing believed the current single transducer design 
meets this intent.
    Boeing claimed the current 737 NG airplane rudder pedal design 
satisfies the parameter 88 requirements defined in the existing rule. 
Boeing added that the rudder design on 737-100 through -500 series 
airplanes delivered since August 1998 is identical to that on the 737 
NG airplanes, and retrofit kits are available for this installation in 
airplanes delivered before then. Boeing noted that any change to the 
requirements to which this installation complies would require 
additional retrofit.
    Boeing further stated that the proposed addition of four individual 
rudder pedal force sensors would require a significant number of design 
changes in the rudder control mechanism and to the structure of the 
cockpit floor. The 737 has severely limited space in the area these 
would be placed, which limits design options. At the time the NPRM was 
issued, Boeing and its suppliers had not yet been able to identify a 
design solution that could be implemented without significant 
structural and system changes that would make retrofit complex, 
lengthy, and costly. Boeing added that it expected the design 
definition and implementation of four transducers would take much 
longer than the implementation dates proposed.
    Boeing also argued that four transducers would provide no major 
incremental gain in information. According to Boeing, a single 
transducer allows investigators to determine why the rudder moved, by 
pilot action or system input, but that a single transducer will not 
show whether a pedal jammed. The four transducers would enable Boeing 
to determine whether the rudder moved and may allow determination of 
which pedal was jammed or restricted. However, the four transducers, 
like the single transducer, would not permit determination of why a 
rudder pedal was jammed or restricted, because the jam or restriction 
is also ``upstream'' of the transducers.
    FAA reply: Although specifically requested, the FAA did not receive 
any cost data or time estimates for a four-rudder-pedal sensor retrofit 
as described in the NPRM. While the FAA understands the NTSB's desire 
for the information that such rudder pedal sensors might provide, 
general comments from Boeing indicate that such a retrofit would be 
both time-consuming and costly. The FAA is unaware of a sensor 
currently in production that could meet the design requirements that 
would be necessitated by the NTSB's request. Even if such a sensor does 
exist, Boeing also indicated (in its comment and in discussions with 
the FAA) that major redesign of the aircraft might be necessary, 
including moving a floor beam, since there is so little space available 
under the rudder pedals of the 737. Such modifications would take 
several years to design and incorporate into the production line; the 
engineering for in-service airplanes would be more complicated, since 
changes to major structural components would mean a change to the 
airplane's original type design and the airworthiness certification of 
every affected airplane. The time that such design and retrofit would 
take far exceeds any recommendation of the NTSB, and argues against the 
NTSB's own characterization of the modification as time-sensitive.
    Further, the FAA is unable to say with any certainty that the 
information that might be gathered by the NTSB's proposed pedal force 
sensors would lead to a solution to the rudder problem. The rudder 
pedal force sensors may well be able to identify the amount of force an 
individual pilot is placing on a pedal, but the amount of force does 
not seem to have been an issue in the noted accidents or incidents. If 
there is a problem in the rudder system, then the amount of force 
exerted in an

[[Page 52388]]

attempt to overcome it is less important than finding where the 
malfunction is occurring. If pilots are fighting each other for control 
using the rudder pedals, then the issue is not with the airplane 
itself. It is a suspected problem with the airplane itself that is the 
reason for proposing this rule, and the FAA has determined that 
continuing to allow compliance with parameter 88 using a single 
midstream transducer reflects the best balance of cost and information 
to be gained in an attempt to locate the source of the problem in a 
timely fashion.
    Accordingly, the FAA has decided against promulgating a four-pedal 
sensor requirement. The agency has no basis for concluding that a 
retrofit of individual rudder pedal sensors would be cost beneficial 
when the costs themselves cannot readily be estimated without a 
significant investment of time and energy. Moreover, since the FAA is 
unable to quantify the requirements either for the equipment or the 
recording rate and sensitivity, any information on estimated costs 
becomes that much less reliable and certainly falls short of the legal 
requirements for imposing the eventual cost on operators.

B. Compliance Issues for the Control Column and Control Wheel

    Proposal: Parameter (a)(88) requires that control wheel and control 
column input forces be measured and recorded. The current rule requires 
that airplanes with breakaway capability record both left and right 
side control wheel forces. The FAA noted in the preamble to the NPRM 
that there also are issues of acceptable means of measuring control 
column and control wheel forces. The FAA specifically requested comment 
on the means and costs of measuring these control forces under the 
requirements proposed in this rulemaking.
    Comments: The FAA received comments from Boeing, Alaska, United 
Airlines, ATA, and the NTSB on the control column and control wheel 
systems.
    Boeing stated that to comply with the existing rule for parameter 
(a)(88), Boeing intended to modify the control column and control wheel 
force transducers for DFDR application to achieve the increased force 
range. Boeing would also install new flight control computer hardware 
and software to interface with the new transducers.
    Boeing stated that the retrofit for the 737-100 through -500 series 
airplanes is basically the same as that for the 737 NG airplanes. 
However, it noted the 737-100 through -500 series airplanes include two 
control column force transducers in the same location as the 737 NG 
airplanes, but that the force applied by individual pilots cannot be 
determined because the elevator control systems of the 737-100 through 
-500 series airplanes do not have a jam override device between 
columns.
    Boeing also described the FAA-approved single-wheel force 
transducer design for parameter (a)(88), and stated that it meets the 
intent of the existing rule provided that the left and right control 
wheel positions also are recorded. Boeing stated that the aileron 
system measures both cockpit control positions, but only the left 
side's force. Each pilot's control inputs go through the left side 
force transducer, except in the event of a failure. Boeing added that 
because the FAA does not typically consider dual failures a likely 
event, the proposed configuration should be acceptable.
    Boeing noted that to comply with the existing requirements for 
parameter (a)(88), the control wheel force transducer would have to be 
modified specifically for DFDR application to achieve the increased 
force range. New flight control computer hardware and software would 
have to be installed to interface with the new transducer and the force 
transducer stops would have to be modified to allow the additional 
range.
    Boeing further stated the control wheel retrofit of the 737-100 
through -500 series airplanes is basically the same as that of the 737 
NG airplanes, except that Boeing would add a (new) second control wheel 
position transducer to the first officer's control wheel to allow the 
737-100 through -500 series airplanes' configurations to be identical 
with that of the 737 NG airplanes.
    The NTSB stated that although it is concerned that the current 
control force sensors will not meet the range and accuracy requirements 
of the proposed rule, suitable control force sensors were likely to be 
available by the then proposed compliance dates. The NTSB contended 
that separate sensors to measure the pilot and copilot flight control 
input forces must be used when breakaway features are employed 
(breakaway capability allows either pilot to operate the airplane 
independently).
    Two operators of 737s and the ATA commented that as of the date of 
the NPRM, the required sensors had not yet been developed.
    FAA reply: The primary objection raised by the commenters was that 
the regulation would force early compliance with parameter (a)(88) for 
control wheel and control column forces, and that the sensors required 
to record to Appendix M specifications were not available and had not 
yet been designed. Sensor design and availability are no longer issues 
since all aircraft manufactured after August 19, 2002 have been 
required to meet Appendix M standards for parameter (a)(88). Nor is 
there any need to provide for more than one sensor type since a sensor 
that records to Appendix M standards now exists for use in a retrofit. 
Accordingly, the FAA intends to adopt the rule as originally proposed, 
with the Appendix M standards applicable to all 737s recording all 
functions required by parameter (a)(88) (70 pounds control 
wheel force and 85 pounds control column force).
    The FAA understands that the lateral control system on the 737 has 
an override device between the two control wheels that allows either 
pilot to operate the control wheel independently, but that the primary 
control path for both pilots is through the left cable control path. 
The right control is not usually connected and is used only in the 
event of a failure. A single control wheel force transducer in the left 
cable path records the inputs from both pilots. The FAA agrees that the 
single control wheel force transducer is acceptable, provided the left 
and right control wheel positions are also recorded. The use of a 
single force transducer with two position sensors is acceptable because 
comparison of the two position sensors allows detection of a breakout 
of the override between the control wheels; this breakout allows the 
right cable control path to become active.

C. Compliance Issues; Other Parameters

1. Standby Rudder Status
    Proposal: In the NPRM, the FAA proposed to add recording of the 
standby rudder status. The standby rudder system is an alternative 
source of hydraulic power to the rudder that is used when primary 
hydraulic power is lost. The intent of the proposed requirement was to 
record whether the standby rudder system switch is in the on or off 
position.
    Comment: Boeing believed the intent of recording the standby rudder 
status was to determine the actual status of the standby rudder system 
and not the position of any particular switch. Boeing indicated that 
the system should record the state of the standby hydraulic rudder 
shutoff valve, which also is controlled by both of the standby rudder 
system switches. Boeing maintained this would provide a clearer 
indication of the actual status of the standby rudder

[[Page 52389]]

system than recording whether the standby rudder switch is in the on or 
off position. The ATA stated that the sensors for the standby rudder 
status parameter have not been designed for any 737.
    FAA reply: The FAA agrees with the comments and we have revised the 
proposed language in paragraph (a)(91) to indicate that it is the valve 
position that needs to be recorded for standby rudder status, not the 
position of the switch, as initially proposed.
2. Thrust Reverser
    Proposal: Under the 1997 DFDR regulations, instrumentation of the 
thrust reversers (Sec.  121.344(a)(22)) was not required until the year 
2001 for some airplanes and is not required at all for older airplanes. 
The proposal would require all 737s regardless of age to record the 
thrust reverser position.
    Comment: Boeing stated that the requirement for recording thrust 
reverser positions would require modifications to the engine accessory 
unit (EAU) to monitor the thrust reverser. According to Boeing, 
approximately 937 737-100 and -200 airplanes will require two new PC 
cards and associated connectors and wiring, and approximately 250 737-
300 and -400 airplanes will require four new PC cards and associated 
connectors and wiring if the proposal is adopted. Boeing requested that 
the FAA not require instrumentation of the thrust reversers for the 
older 737-100 through -500 series airplanes. The 737 NG airplanes would 
be retrofitted to record thrust reverser position. Boeing suggested 
specific language that could be used to codify its request.
    FAA reply: The SNPRM does not incorporate Boeing's suggested 
change. Under Sec.  121.344(b)(1), adopted in 1997, the only airplanes 
not required to record thrust reverser position, parameter (a)(22), are 
airplanes manufactured on or before October 11, 1991, that were not 
equipped with a FDAU as of July 16, 1996. All other airplanes must 
either be retrofitted to record, or record at manufacture, thrust 
reverser position.
    The distinction made in Sec.  121.344(b)(1) was introduced to 
prevent the oldest airplanes from having to be retrofitted with a FDAU 
to meet the 1997 rule, not because thrust reverser data is not 
important. Under this SNPRM, the other recording requirements for 737s 
necessitate the installation of a FDAU, eliminating the distinction 
made in the 1997 rule. Further, the FAA cannot accept Boeing's 
suggested language because it is general and would relieve not only 
737s but certain other airplanes from the 1997 requirement to record 
parameter (a)(22). This proposal would require all 737s to record 
parameter (a)(22).
3. Yaw Damper Status and Yaw Damper Command
    Proposal: Proposed paragraph (a)(89) would add the recordation of 
yaw damper status. The intent of the requirement is to determine 
whether the yaw damper is on or off. Proposed paragraph (a)(90) would 
add the recordation of yaw damper command. The intent of this 
requirement is to record the amount of voltage being received by the 
yaw damper system. This determines how much rudder movement is being 
commanded.
    Comment: For the 737-100 through -500 series airplanes, Boeing 
proposed to record the yaw damper linear variable displacement 
transducer (LVDT) position feedback from the new yaw damper coupler 
through an ARINC 429 interface, and, if the DFDR capacity allows, the 
yaw damper command from the yaw damper coupler through an ARINC 429 
interface. Boeing noted that the 737 NG airplanes record both the yaw 
damper command from the stall management yaw damper and the yaw damper 
LVDT position feedback through an ARINC 429 interface. The ATA stated 
that sensors for yaw damper status and yaw damper command parameters 
are not addressed in a retrofit service bulletin.
    FAA reply: Sensors for the yaw damper status and yaw damper command 
parameters have been developed and have been installed in 737s 
manufactured since August 18, 2000. The sensors exist and the FAA 
continues to believe that the parameters should be required.
4. Other Issues
    Proposal: The current DFDR regulation allows single-source 
recording for control input and control surface positions, parameters 
(a)(12) through (a)(14) or (a)(12) through (a)(17), depending on the 
date of airplane manufacture. The proposed rule eliminated the 
allowance to record these from a single source.
    Comments: Boeing stated that Sec.  121.344(b) and (c), as proposed, 
removes the allowance to permit recording parameters (a)(12) through 
(a)(17) from a single source and applies the full requirement of 
appendix M to part 121 to recording these parameters. However, 
paragraph (d) still permits recording parameters (a)(12) through 
(a)(17) from a single source.
    FAA reply: Removing the allowance for recording control and surface 
positions from a single source was an error in the proposed rule. This 
SNPRM includes the single-source recording as provided in the 1997 
rule. A sentence has been added in Sec.  121.344(m) indicating that 
single-source recording would remain available to airplanes otherwise 
subject to Sec.  121.344(b)(1), (c)(1), or (d)(1).
    Proposal: The proposal removes 737s from the requirements of Sec.  
121.344(b) and (c), adds specific 737 requirements to Sec.  121.344(d), 
(e), and (f), and adds new Sec.  121.344(m).
    Comments: Boeing indicated that Sec.  121.344(d), (e), and (f), as 
proposed, state that all 737s must comply with the requirements in 
paragraphs (m)(1) and (m)(2). Boeing contended this language overlooks 
the requirements of paragraph (m). Boeing also did not understand why 
paragraphs (d), (e), and (f) were not revised as paragraphs (b) and (c) 
to except the 737. Boeing stated that the addition of paragraph (m) 
makes it unclear as to what is required for 737s and that it would be 
much clearer to include the additional 737 requirements in the existing 
applicable paragraphs. Boeing further stated that Sec.  121.344(m), as 
proposed, is inconsistent with paragraphs (b), (c), and (d) in that it 
requires recording parameters (a)(88) through (a)(91), while paragraphs 
(b), (c), and (d) do not.
    FAA reply: The modifications to the compliance schedule for 
installation of the additional parameters have removed the issue of 
compliance time; compliance time is no longer determined by the date of 
FDAU installation.
    For consistency, Sec.  121.344(b), (c), (d), (e), and (f) are 
similarly revised to reference the 737 requirements in Sec.  
121.344(m). The FAA has decided against putting the 737 requirements in 
each subparagraph because it would be cumbersome, unnecessarily 
repetitive, and introduce more possibilities for error.
    Proposal: The note to parameter (a)(88) in current Appendix M to 
part 121 requires airplanes that have a flight control breakaway 
capability (which allows either pilot to operate controls 
independently) to record both control force inputs; the note also 
discusses sampling rates.
    Comments: Boeing pointed out that the note to parameter 88 in 
appendix M to part 121 and appendix E to part 125 indicates that all 
the comments in the remarks column do not apply to the 737. Boeing 
believed that the note is meant to indicate that it is only the 
sampling interval remarks that do not apply to the 737s. The NTSB also 
stated that the remarks section covers, in addition to the sampling 
rate requirements, a

[[Page 52390]]

requirement to record both control force inputs for those airplanes 
that have a flight control breakaway capability that allows either 
pilot to independently operate the airplane, which still would apply to 
737s.
    FAA reply: The FAA agrees with Boeing, and has revised footnote 18 
to clarify application of the parameter for 737s. The requirement to 
record both control force inputs for systems with breakaway 
capabilities does apply to the 737, but as discussed above, the FAA has 
approved the use of a single control wheel force transducer provided 
that both control wheel positions are recorded (although both pilot's 
inputs go through the left side force transducer, except in the event 
of a failure). Because the FAA historically has not considered a dual 
failure a likely event, this configuration is acceptable.
    Proposal: The FAA proposed the same changes to the digital flight 
data recorder regulations in Sec.  125.226 as those proposed in Sec.  
121.344. In addition, the FAA proposed the same changes to Appendix E 
to part 125 as those proposed to Appendix M to part 121. The FAA also 
proposed that airplanes operating under deviation authority from part 
125 must comply with the flight data recorder requirements of part 125 
for the particular aircraft. The FAA specified that this deviation 
requirement would apply to all aircraft and not only the 737. The FAA 
specifically sought comments on why the flight data recorder 
requirements of part 125 should not be made applicable to aircraft 
operated under deviation authority. In addition, the FAA sought 
comments from affected persons operating aircraft under deviation 
authority from part 125 concerning the proposed compliance schedule.
    Comments: The FAA received no comments on the proposed changes to 
part 125. Accordingly, the changes to part 91, applicable to part 125 
airplanes operated under deviation authority, and the changes to part 
125 and Appendix E are proposed again here without change from the 
original proposal.

IV. Changes Adopted in This SNPRM

    When the FAA proposed the recordation of new flight data recorder 
parameters in November 1999, the ETEB was still in the process of 
conducting its failure analysis, and other action by the agency was not 
yet contemplated. The ETEB's finding and the FAA's subsequent decision 
to issue the AD requiring replacement of the rudder system mandate that 
this rule be modified to account for those actions.
    This proposed rule, if adopted, would require the installation of 
the flight recorder parameters proposed in the NPRM with the following 
modifications. The installation would be accomplished simultaneously 
with the installation of the redesigned rudder system in order to 
minimize the costs and out-of-service time required. The regulatory 
evaluation for this proposed rule has been significantly revised to 
include this extended compliance time. This extension of the compliance 
time also addresses the majority of the comments received in response 
to the proposed rule. Specifically, this SNPRM incorporates the 
following changes:
     Sections 121.344(b), (c), (d), (e), and (f) and Sec.  
125.226(b), (c), (d), (e), and (f) would be amended to indicate that 
all 737 model airplanes also must comply with the requirements in Sec.  
121.344(m) or Sec.  125.226(m), respectively. Sections 121.344(m) and 
125.226(m) would be added to indicate that in addition to other 
applicable requirements, all 737 model airplanes must record the 
parameters listed in paragraphs (a)(1) through (a)(22) and (a)(88) 
through (a)(91) in accordance with the ranges, accuracies, resolutions, 
and recording intervals specified in Appendix M to part 121 or Appendix 
E to part 125, respectively. The proposed compliance times have been 
changed to state that the installation of the equipment required to 
record these parameters must be accomplished during the installation of 
the modified rudder system required by AD or no later than November 
2008. These sections would also reinstate the language allowing single-
source recording, as discussed in the disposition of comments. The 
parameters that may be recorded from a single source would be 
determined by the age of the airplane and its applicable regulations.
     Footnote 18 would be added to parameter 88 in Appendix M 
to part 121 and Appendix E to part 125 and would read ``For all 737 
model airplanes: The seconds per sampling interval is 0.5 per control 
input; the remarks regarding the sampling rate do not apply; a single 
control wheel force transducer installed on the left cable control is 
acceptable provided the left and right control wheel positions also are 
recorded.'' Footnote 19 would be added to parameter 88 in Appendix M to 
part 121 and Appendix E to part 125 and would read ``For all 737 model 
airplanes manufactured on or before January 31, 2001, Rang