[Federal Register Volume 59, Number 21 (Tuesday, February 1, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-347]


[[Page Unknown]]

[Federal Register: February 1, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 93-NM-79-AD; Amendment 39-8789; AD 94-01-07]

 

Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737 series airplanes, that requires 
repetitive tests of the main rudder power control unit (PCU) to detect 
excessive internal leakage of hydraulic fluid, stalling, or reversal, 
and the eventual replacement of the main rudder PCU with an improved 
model. This amendment is prompted by results of an investigation which 
revealed that the secondary slide in the servo valve of certain PCU's 
can go past the intended maximum-travel position. The actions specified 
by this AD are intended to prevent secondary slide overtravel from 
occurring, which could cause the rudder actuator piston and the rudder 
to operate with reduced force capability or to move in a direction 
opposite to the intended direction; this could result in reduced 
controllability of the airplane.

DATES: Effective March 3, 1994.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of March 3, 1994.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.

FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer, 
Seattle Aircraft Certification Office, Systems & Equipment Branch, ANM-
130S, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056; telephone (206) 227-2673; fax (206) 227-
1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations to include an airworthiness directive (AD) that is 
applicable to certain Boeing Model 737 series airplanes was published 
in the Federal Register on August 16, 1993 (58 FR 43301). That action 
proposed to require periodic tests of the main rudder PCU to detect 
excessive internal leakage of hydraulic fluid, stalling, or reversal, 
and the correction of discrepancies. That action also proposed to 
require the eventual replacement of the main rudder PCU with an 
improved model; such replacement would constitute terminating action 
for the periodic tests.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    Several commenters request that the proposed rule be revised to 
require a one-time internal leakage test of the PCU, instead of the 
proposed repetitive tests every 750 flight hours. These commenters 
consider that the existing pre-flight controls check is adequate to 
detect rudder control anomalies that would be due to dual servo valve 
secondary slide overtravel; since this check is performed prior to each 
flight, it will verify the function of the rudder control system on a 
regular basis. These commenters believe that the proposed repetitive 
test is not appropriate or reliable, since it is sensitive to variables 
such as temperature and the inspecting technician's individual 
technique and judgment. In addition, some of these commenters believe 
that the secondary slide overtravel problems are attributable to either 
adverse tolerance build-up or improper assembly of the PCU during 
manufacture, and are not due to wear or deterioration of the valve over 
time; therefore, these commenters consider that repetitive tests are 
unnecessary. One commenter states that the proposed test has not proved 
to be reliable in identifying rudder PCU anomalies, and that this test 
could cause a rise in the number of removals of PCU's that would 
typically be serviceable; this would have a severe economic impact on 
affected operators.
    The FAA does not concur with the commenters' request. First, the 
FAA notes that rapid rudder inputs are a factor in uncovering rudder 
control anomalies. During a pre-flight check, the flight crew may not 
cycle the rudder PCU at a rate fast enough to uncover secondary slide 
overtravel. For this reason, the FAA does not agree that all rudder 
control anomalies due to secondary slide overtravel can be detected 
during pre-flight checks.
    Second, although the FAA agrees that the required repetitive test 
is not completely repeatable and could be subject to the judgment of 
the technician, the FAA recognizes it as a written procedure for 
maintenance crews to follow, which emphasizes cycling of the rudder 
pedals at a maximum rate. While this test cannot ensure that the 
secondary slide overtravel anomaly does not exist, it can detect 
certain conditions that contribute to secondary slide overtravel. For 
example, the overtravel anomaly, combined with either (1) A secondary 
summing arm missing its stop or (2) a primary slide jamming to the 
secondary slide, would be detected during the repetitive test. During 
bench testing on one PCU, the secondary summing arm was observed 
hitting its stop on some occasions and missing it on others; this 
intermittent condition, if combined with the secondary overtravel 
anomaly and rapid rudder inputs, could cause rudder control problems. 
For these reasons, the FAA has determined that the required repetitive 
tests will contribute to flight safety because they exercise the rudder 
pedals at a rapid rate and they can detect high internal leakage within 
the servo valve.
    Several commenters request that the compliance time for replacing 
the main rudder PCU be extended from the proposed 5 years to at least 7 
years. These commenters state that such an extension is necessary to 
avoid the economic burden to operators that would be caused by a 
campaign of scheduled removals. A 7-year compliance time would 
correspond to a typical overhaul period for the main rudder PCU, and 
would avoid unscheduled removal of PCU's that exhibit no operational 
anomalies. Some commenters note that the design feature that allows 
secondary slide overtravel has existed for over 25 years and, over that 
time period, has accumulated 55 million flight hours in the affected 
fleet with no known in-flight control problems. These commenters state 
that it would be extremely rare for the problem condition to exist in 
combination with other factors so as to result in a reduction of rudder 
control capability. For these reasons, these commenters consider that 
extending the compliance time for completion of the replacement would 
not appreciably affect the safety of the fleet.
    The FAA does not concur with the commenters' request to extend the 
compliance time for replacement of the PCU. Although the FAA 
acknowledges that no known in-flight control problems have been 
documented on Model 737 airplanes with regard to the subject condition, 
the FAA does recognize that two PCU's have been removed from Model 737 
series airplanes after the pilot identified rudder control problems 
during the pre-flight check. In developing an appropriate compliance 
time for this action, the FAA considered the safety implications of 
incidents such as these, the availability of required parts, and the 
normal maintenance schedules for timely accomplishment of the 
replacement. Further, only the original equipment manufacturer 
possesses approved data allowing it to accomplish the rework of the 
affected PCU's; therefore, the compliance time also was based on the 
capability of this manufacturer to schedule and modify all of the 
affected servo valves. In light of these items, the FAA has determined 
that 5 years for compliance is appropriate. The FAA considers that a 5-
year compliance time allows ample time for all affected PCU's to be 
modified by the manufacturer, without creating a burden on either the 
operators or the manufacturer. Five years also allows ample time for 
the replacement to be accomplished coincidentally with scheduled major 
airplane inspection and maintenance activities, thereby minimizing the 
costs associated with special airplane scheduling. However, paragraph 
(c) of the final rule does provide affected operators the opportunity 
to apply for an adjustment of the compliance time if data is presented 
to justify such an adjustment.
    One commenter strongly supports the proposed rule, but considers 
that the 5-year compliance time for replacement of the PCU's is too 
long. This commenter requests that replacement of all affected PCU's 
should begin immediately as replacement parts become available, instead 
of allowing operators to operate airplanes equipped with potentially 
defective PCU's for up to 5 years. This commenter notes that the 
addressed anomaly was first discovered in July 1992 and, by the time 
the proposed rule becomes effective and the end of the 5-year 
compliance period is reached, approximately 7 years will have elapsed 
since then. This amount of time is too long, considering the 
significance of the addressed unsafe condition.
    The FAA does not concur with the commenter's request to shorten the 
compliance time for replacement of the PCU's. For the same reasons 
explained previously, the FAA has determined that a 5-year compliance 
time is appropriate. The repetitive tests of the PCU required by this 
AD will provide an acceptable level of safety in the interim. 
Additionally, the commenter should not assume that all operators will 
wait until the end of the compliance time before replacement the PCU's. 
In fact, the FAA has been advised that the PCU manufacturer has already 
begun rework activity and some airlines have already begun replacement 
procedures.
    One commenter requests that paragraph (a)(2) of the proposed rule 
be revised to provide operators with the option of installing a 
serviceable, non-modified PCU, rather than only a modified PCU, if a 
discrepancy is detected during any test. Operators should be allowed to 
use this non-modified PCU, provided that it is repetitively tested 
until replacement of all PCU's is required in 5 years. Such a revision 
to the rule would prevent unnecessary grounding of an airplane if a 
discrepancy is detected and a modified PCU is not available. The FAA 
concurs and has revised the final rule accordingly.
    Another commenter requests that the proposed rule be revised to 
address third-party repaired parts. This commenter states that at least 
one repair facility is producing FAA-approved replacement slide and 
sleeve assemblies to overhaul the Parker-Hannifin main rudder PCU dual 
servo valves. The commenter believes that it is the FAA's 
responsibility to ensure that third-party replacement parts are 
reworked in a controlled manner to the same level of safety as that 
provided by the retrofit plan developed by the original equipment 
manufacturer (OEM), since the replacement parts were approved solely by 
the FAA without support from the OEM.
    The FAA does not concur that such a revision to the rule is 
necessary. Paragraph (c) of the final rule contains a provision that 
allows third-party replacement part manufacturers to submit proposed 
design changes to the FAA for approval as alternative methods of 
compliance with the AD.
    One commenter suggests that the discussion of the requirements of 
the proposed rule be revised to clarify that the test of the main 
rudder PCU is necessary not only to detect excessive internal leakage 
of hydraulic fluid, but to detect and correct possible stalling and 
reversal as well. The FAA concurs. Although the test is accomplished to 
detect excessive internal leakage, the AD requires that any 
discrepancy, such as stalling and reversal, that is detected during the 
test must be corrected prior to further flight. The AD references 
Boeing Service Letter 737-SL-27-82-B for a description of the possible 
discrepancies that could be found during the required test. The wording 
to the preamble of this final rule has been revised to include 
reference to the possible discrepancies of stalling and reversal; 
however, the wording of the AD itself needs no revision.
    This same commenter suggests that the description of the unsafe 
condition on which this AD action is based could be worded more 
accurately. This commenter states that the actions specified by the AD 
are intended to prevent secondary slide overtravel from occurring, 
which could cause the rudder actuator piston and the rudder to 
``operate with reduced force capability or to move in a direction 
opposite to the intended direction.'' The FAA concurs with the 
commenter's suggestion and has revised the appropriate wording 
accordingly.
    Two commenters suggest that the cost impact information in the 
preamble to the notice was not totally accurate in showing the complete 
costs to operators, especially those costs related to the required 
repetitive tests. One commenter states that each test would require 
approximately 8 work hours to accomplish, and that, based on the 750-
flight hour repetitive test interval, most airplanes would be required 
to be tested between 6 and 10 times over the next 5 years (until 
replacement of the PCU is completed). Another commenter states that the 
total time required for removing and installing the PCU is 20 work 
hours. The FAA concurs that the economic information should be 
clarified. The cost impact figures, as stated in the preamble to the 
notice, were based on the latest data that the FAA had at that time. 
The cost impact information, below, has been revised to delineate the 
costs of the required actions, based on this latest information 
provided by the commenters.
    Paragraphs (a)(1) and (a)(2) of the final rule have been revised to 
correctly reference paragraph ``3.B.'' of Boeing Service Letter 737-SL-
27-82-B for the description of possible discrepancies that could be 
found during the required test. The notice had incorrectly referenced 
paragraph ``B.'' rather than ``3.B.''
    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule with the changes previously 
described. The FAA has determined that these changes will neither 
significantly increase the economic burden on any operator nor increase 
the scope of the AD.
    There are approximately 2,448 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 729 
airplanes of U.S. registry will be affected by this AD.
    It will take approximately 8 work hours per airplane to accomplish 
the required test actions, at an average labor rate of $55 per work 
hour. Based on these figures, the total cost impact of the tests 
required by this AD on U.S. operators is estimated to be $320,760, or 
$440 per airplane, per test.
    According to information provided by commenters to the notice that 
preceded this rule, some airplanes may require to be tested between 6 
and 10 times prior to the required replacement of the PCU (within 5 
years). In the case of those airplanes requiring 6 tests, the total 
cost impact of the required repetitive tests would be $2,640 per 
airplane over 5 years; in the case of those airplanes requiring 10 
tests, the total cost impact of the required repetitive tests would be 
$4,400 per airplane over 5 years.
    The number of required work hours, as indicated above, is presented 
as if the tests required by this AD were to be conducted as ``stand 
alone'' actions. However, in actual practice, these tests could be 
accomplished coincidentally or in combination with normally scheduled 
airplane inspections and other maintenance program tasks. Therefore, 
the actual number of necessary ``additional'' work hours would be 
minimal in many instances. Additionally, any costs associated with 
special airplane scheduling should be minimal.
    It will take approximately 20 work hours per airplane to accomplish 
the required replacement of the PCU (removal and installation), at an 
average labor rate of $55 per work hour. Required parts will be 
supplied by the manufacturer at no cost to operators. Based on these 
figures, the total cost impact of the replacement required by this AD 
is estimated to be $801,900, or $1,100 per airplane.
    The 5-year compliance time for the replacement of the PCU, as 
specified in paragraph (b) of this AD, will allow ample time for the 
replacement to be accomplished coincidentally with scheduled major 
airplane inspection and maintenance activities, thereby minimizing the 
costs associated with special airplane scheduling.
    The total cost impact figures described above are based on 
assumptions that no operator has yet accomplished any of the 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted. However, the 
FAA has been advised that several operators already have accomplished 
at least the initial required test of the PCU's on their affected 
fleets, and certain operators already have replaced some PCU's. 
Therefore, the future economic cost impact of this rule on U.S. 
operators is less than that indicated above.
    The regulations adopted herein will not have substantial direct 
effects 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, in 
accordance with Executive Order 12612, it is determined that this final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

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

    Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.


Sec. 39.13  [Amended]

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

94-01-07 Boeing: Amendment 39-8789. Docket 93-NM-79-AD.

    Applicability: Model 737 series airplanes; line positions 1 
through 2453, inclusive; certificated in any category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent the rudder actuator piston and the rudder to operate 
with reduced force capability or to move in a direction opposite to 
the intended direction, which could result in reduced 
controllability of the airplane, accomplish the following:
    (a) Within 750 flight hours after the effective date of this AD, 
perform a test of the main rudder power control unit (PCU), part 
number 65-44861-2/-3/-4/-5/-6/-7/-8/-9, to detect internal leakage 
of hydraulic fluid, in accordance with Boeing Service Letter 737-SL-
27-82-B, dated July 13, 1993.
    (1) If no discrepancy, as described in paragraph 3.B. of the 
Service Letter, is detected, repeat the test at intervals not to 
exceed 750 flight hours.
    (2) If any discrepancy, as described in paragraph 3.B. of the 
Service Letter, is detected during any check, prior to further 
flight, accomplish either paragraph (a)(2)(i) or (a)(2)(ii) of this 
AD:
    (i) Replace the main rudder PCU with a serviceable PCU in 
accordance with the Model 737 Overhaul Manual. After such 
replacement, repeat the test at intervals not to exceed 750 flight 
hours.
    (ii) Replace the main rudder PCU with a new main rudder PCU 
having part number 65-44861-11 or 65C37052-2/-3/-4/-5/-6/-7/-8/-9, 
in accordance with Boeing Service Bulletin 737-27-1185, dated April 
15, 1993. Such replacement constitutes terminating action for the 
tests required by this AD.
    (b) Within 5 years after the effective date of this AD, replace 
the main rudder PCU, part number 65-44861-(  ), with a new main 
rudder PCU having part number 65-44861-11 or 65C37052-2/-3/-4/-5/-6/
-7/-8/-9, in accordance with Boeing Service Bulletin 737-27-1185, 
dated April 15, 1993. Such replacement constitutes terminating 
action for the tests required by this AD.
    (c) 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, Transport Airplane Directorate. 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: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (d) Special flight permits may be issued in accordance with FAR 
21.197 and 21.199 to operate the airplane to a location where the 
requirements of this AD can be accomplished, provided that the 
airplane has not failed the internal leakage test required by this 
AD.
    (e) The tests shall be done in accordance with Boeing Service 
Letter 737-SL-27-82-B, dated July 13, 1993. The replacement shall be 
done in accordance with Boeing Service Bulletin 737-27-1185, dated 
April 15, 1993. This incorporation by reference was approved by the 
Director of the Federal Register in accordance with 5 U.S.C. 552(a) 
and 1 CFR part 51. Copies may be obtained from Boeing Commercial 
Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. 
Copies may be inspected at the FAA, Transport Airplane Directorate, 
1601 Lind Avenue, SW., Renton, Washington; or at the Office of the 
Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.
    (f) This amendment becomes effective on March 3, 1994.

    Issued in Renton, Washington, on January 3, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-347 Filed 1-31-94; 8:45 am]
BILLING CODE 4910-13-P