[Federal Register Volume 66, Number 175 (Monday, September 10, 2001)]
[Proposed Rules]
[Pages 46968-46971]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-22589]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2001-NM-41-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 727-100 and 727-200 Series 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 727-100 and 
727-

[[Page 46969]]

200 series airplanes. This proposal would require replacement of the 
installed autopilot pitch control computer with a modified computer, 
testing of the modified system, and revision of the Airplane Flight 
Manual (AFM). This action is necessary to prevent undesirable and 
potentially dangerous pitch oscillations during coupled instrument 
landing systems (ILS) approaches. This action is intended to address 
the identified unsafe condition.

DATES: Comments must be received by October 25, 2001.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2001-NM-41-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9 a.m. and 3 p.m., Monday through Friday, except 
Federal holidays. Comments may be submitted via fax to (425) 227-1232. 
Comments may also be sent via the Internet using the following address: 
[email protected]. Comments sent via fax or the Internet must 
contain ``Docket No. 2001-NM-41-AD'' in the subject line and need not 
be submitted in triplicate. Comments sent via the Internet as attached 
electronic files must be formatted in Microsoft Word 97 for Windows or 
ASCII text.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Thanh Truong, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-
4056; telephone (425) 227-2552; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this action may be changed in 
light of the comments received.
    Submit comments using the following format:
     Organize comments issue-by-issue. For example, discuss a 
request to change the compliance time and a request to change the 
service bulletin reference as two separate issues.
     For each issue, state what specific change to the proposed 
AD is being requested.
     Include justification (e.g., reasons or data) for each 
request.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 2001-NM-41-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 2001-NM-41-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received a report indicating that, on February 9, 1998, 
a Boeing Model 727 series airplane was involved in an accident during a 
coupled instrument landing system (ILS) category II approach at Chicago 
O'Hare International Airport. The approach was normal until the 
airplane passed through 200 feet above ground level, where the airplane 
started a pitch oscillation that continued to increase. The airplane 
descended below the ILS glide slope, then climbed above it, and finally 
descended below it again, impacting the ground 300 feet short of the 
runway threshold. Upon impact, the airplane slid over the threshold and 
off the right side of the runway, where it came to rest. Twenty-two 
passengers and one flight attendant sustained minor injuries. The 
airplane was extensively damaged.
    The National Transportation Safety Board (NTSB), in investigating 
the accident, has determined that the existence of an autopilot system 
anomaly can, under certain conditions, produce undesirable pitch 
oscillations in the Model 727-100 and -200. The ILS provides electronic 
signals to guide the pilot and autopilot in flying the airplane to the 
runway. The glide slope is usually determined from a 3-degree flight 
path to a point about 1,000 feet down the runway from the approach end. 
Electronic signals are processed on the airplane and instruments 
indicate whether the airplane is on the localizer and glide slope or 
indicate how much, and in which direction, the airplane has deviated 
from them. The information provided to the pilot via displays on the 
instrument panel, or directly to the autopilot, indicate whether the 
airplane should continue on course or fly up, down, left, or right to 
get back on course.
    Because glide slope deviations close to the runway require smaller 
pitch corrections than those required far from the runway, the 
autopilot sensitivity has to be reduced as the airplane nears the 
runway. This process, called desensitization, depends on distance from 
the runway, but if the ILS does not provide distance measuring 
equipment, this is sometimes calculated by measuring time elapsed since 
passing a point of known distance from the runway and muliplying the 
measured time by an assumed ground speed. This time-based method was 
used by the Sperry SP-150 autopilot installed on the accident airplane. 
The system was set up to start desensitizing over a period of 150 
seconds after passing through a radio altitude of 1,500 feet. Upon 
receiving the middle marker signal on the ILS approach, the speed of 
desensitization would increase.
    A characteristic of the time-based method of desensitizing the 
autopilot is that the gain will be scheduled correctly only if the 
ground speed is relatively close to the ground speed the autopilot 
designers assumed when selecting the time period required for 
desensitization. If the ground speed is higher than the ground speed 
assumed in the autopilot design, the airplane will approach the runway 
before the desensitization period expires and the sensitivity will be 
higher than that intended by the design.
    The 150-second desensitization period used by the Sperry SP-50 and 
SP-150 autopilots was optimized for the lower approach airspeeds and a 
40-degree flap setting. However, in the early 1980s, operators started 
landing the Model 727 at 30-degree flap settings, and higher airspeeds, 
in order to

[[Page 46970]]

improve the maneuverability of the airplane during the approach.
    During the NTSB investigation, another pilot described a pitch 
event experienced by another Model 727 series airplane in 1997. That 
airplane was aking a coupled ILS category II approach to a runway at 
Chicago O'Hare International Airport when, at about 250 feet, the crew 
felt a bump and the airplane pitched up in response to being slightly 
below the glide slope. The airplane climbed through the glide slope and 
then pitched down severely to recapture the glide slope. The pilot 
called for a go-around, came back for another approach, and experienced 
the same bump again before diverting to the alternate airport. This 
Model 727 also had a time-based autopilot with a 150-second 
desensitization period. NTSB studies found that at the approach speeds 
of the accident flight, the autopilot with the 150-second 
desensitization period responds to disturbances by commanding 
oscillatory pitch changes that grow in time and result in significant 
deviations from the desired flight path. Based on the NTSB's studies 
and FAA findings, the improper desensitization schedule is considered a 
contributing factor in the destabilized approach of the accident flight 
and in the reported pitch event that occurred in 1997. Therefore, the 
FAA is concerned that other Model 727 series airplanes equipped with 
unmodified SP-50 and SP-150 autopilots could experience, in conditions 
similar to those of the accident flight, undesirable and potentially 
dangerous pitch changes during coupled ILS category II approaches.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
727-22A0093, dated December 20, 2000, which describes procedures for 
replacement of the SP-50 or SP-150 autopilot pitch control computer 
with a modified autopilot pitch control computer and a functional test 
to verify function. Accomplishment of the actions specified in the 
service bulletin is intended to adequately address the identified 
unsafe condition.
    Boeing Alert Service Bulletin 727-22A0093 refers to Sperry Service 
Bulletin 21-1132-121, dated November 23, 1982 (for the SP-50 
autopilots), and Sperry Service Bulletin 21-1132-122, dated February 7, 
1983 (for the SP-150 autopilots), as additional sources of service 
information for accomplishment of the replacement of the autopilot 
pitch control computer and subsequent one-time test.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions specified in 
the service bulletins described previously, except as discussed below. 
The proposed AD would also require two revisions to the FAA-approved 
Airplane Flight Manual (AFM). One revision, required within six months 
after the effective date of the proposed AD, would prohibit a category 
II autopilot coupled ILS approach if the Middle Marker (ground or 
airborne system) is inoperative. This revision would also require that 
the autopilot be disconnected at, or prior to, 80 feet above the 
runway's touchdown-zone elevation during coupled ILS category II 
approaches. The second revision, required after the autopilot 
modification, would limit the approach flap setting to 30 degrees when 
conducting a category II autopilot coupled ILS approach. It should be 
noted that the FAA is conducting additional studies to develop 
operating limitations, as necessary, that address approach flap 
settings and airspeeds specifically, and also considering other aspects 
such as winds and glideslope angles.

Differences Between the Proposed AD and the Service Bulletin

    Operators should note that the service bulletin recommends 
accomplishing the replacement ``at the earliest convenience'' (after 
the release of the service bulletin). The FAA, however, has determined 
that performing the replacement ``at the earliest convenience'' may not 
address the identified unsafe condition in a timely manner. In 
developing an appropriate compliance time for this AD, the FAA 
considered not only the manufacturer's recommendation, but the degree 
of urgency associated with addressing the subject unsafe condition, the 
average utilization of the affected fleet, and the time necessary to 
perform the replacement (approximately 2 hours). In light of all of 
these factors, the FAA finds an 18-month compliance time for completing 
the required actions to be warranted, in that it represents an 
appropriate interval of time allowable for affected airplanes to 
continue to operate without compromising safety.
    Operators should also note that, although the service bulletin 
recommends performing a functional test in accordance with the 727 
Maintenance Manual, the proposed AD would require accomplishment of the 
more detailed functional test in accordance with Sperry Service 
Bulletins 21-1132-121 or 21-1132-122, as applicable.

Cost Impact

    There are approximately 750 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 162 airplanes of U.S. registry 
would be affected by this proposed AD, that it would take approximately 
1 work hour per airplane to accomplish the proposed AFM revisions, and 
that the average labor rate is $60 per work hour. Based on this figure, 
the cost impact of the proposed AFM revisions on U.S. operators is 
estimated to be $9,720, or $60 per airplane.
    It would take approximately 1 work hour per airplane to accomplish 
the proposed replacement and functional test of the SP-50 autopilot. 
Estimated costs for required parts would be $1. It would take 
approximately 2 work hours per airplane to accomplish the proposed 
replacement and functional test of the SP-150 Autopilot. Estimated 
costs for required parts would be $168. Based on these figures, the 
cost impact of the proposed replacement and functional test on U.S. 
operators is estimated to be between $9,882 and $46,656, or between $61 
and $288 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this proposed AD were not adopted. The cost impact 
figures discussed in AD rulemaking actions represent only the time 
necessary to perform the specific actions actually required by the AD. 
These figures typically do not include incidental costs, such as the 
time required to gain access and close up, planning time, or time 
necessitated by other administrative actions.

Regulatory Impact

    The regulations proposed herein would not have a substantial direct 
effect on the States, on the relationship between the national 
Government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44

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FR 11034, February 26, 1979); and (3) if promulgated, will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act. A copy of the draft regulatory evaluation prepared for 
this action is contained in the Rules Docket. A copy of it may be 
obtained by contacting the Rules Docket at the location provided under 
the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 2001-NM-41-AD.

    Applicability: Model 727-100 and 727-200 series airplanes, 
certificated in any category, as listed in Boeing Alert Service 
Bulletin 727-22A0093, dated December 20, 2000.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (f) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent undesirable and potentially dangerous pitch 
oscillations during coupled instrument landing systems (ILS) 
approaches, accomplish the following:

Revision of Airplane Flight Manual

    (a) Within six months after the effective date of this AD, 
revise the Limitations Section of the FAA-approved Airplane Flight 
Manual (AFM) by adding the following paragraphs under AUTOPILOT/
FLIGHT DIRECTOR SYSTEM. This may be accomplished by inserting a copy 
of this AD into the AFM.
    ``CAT II autopilot coupled ILS approach shall not be performed 
if the Middle Marker (ground or airborne system) is inoperative.
    Disconnect the autopilot at, or prior to, 80 ft. (above the 
runway's touchdown-zone elevation) during Cat II autopilot coupled 
ILS approaches.''

Modification and Testing of Autopilot

    (b) Within 18 months after the effective date of this AD, 
replace the existing SP-50 or SP-150 single channel autopilot with a 
modified single channel autopilot in accordance with Boeing Alert 
Service Bulletin 727-22A0093, dated December 20, 2000.
    (c) Concurrent with the modifications required by paragraph (b) 
of this AD, and before reinstallation of the modified autopilot and 
further flight, perform a one-time test procedure of the modified 
autopilot in accordance with Sperry Service Bulletin 21-1132-121, 
dated November 23, 1982 (for SP-50 autopilots), or 21-1132-122, 
dated February 7, 1983 (for SP-150 autopilots), as applicable.

Post-Modification Revision of Airplane Flight Manual

    (d) Before further flight after performing the replacement 
required by paragraph (b) of this AD, revise the Limitations Section 
of the AFM by adding the following paragraph under AUTOPILOT/FLIGHT 
DIRECTOR SYSTEM. This may be accomplished by inserting a copy of 
this AD into the AFM.
    ``Limit the approach flap setting to 30 degrees when conducting 
CAT II autopilot coupled ILS approach.''

Spare Parts

    (e) As of the effective date of this AD, no person shall install 
on any airplane an autopilot pitch control computer unless it has 
been modified and the applicable AFM has been revised in accordance 
with this AD.

Alternative Methods of Compliance

    (f) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA. Operators shall submit their requests through an 
appropriate FAA Principal Maintenance Inspector, who may add 
comments and then send it to the Manager, Seattle ACO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (g) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on August 31, 2001.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-22589 Filed 9-7-01; 8:45 am]
BILLING CODE 4910-13-P