[Federal Register Volume 62, Number 86 (Monday, May 5, 1997)]
[Rules and Regulations]
[Pages 24325-24328]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-11201]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-151-AD; Amendment 39-10011; AD 97-09-15]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 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 all Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes, that requires a one-time inspection to determine the 
part number of the engage solenoid valve of the yaw damper, and 
replacement of the valve with a valve having a different part number, 
if necessary. This amendment is prompted by a review of the design of 
the flight control systems on Model 737 series airplanes. The actions 
specified by this AD are intended to prevent sudden uncommanded yawing 
of the airplane due to potential failures within the yaw damper system, 
and consequent injury to passengers and crewmembers.

EFFECTIVE DATE: June 9, 1997.

ADDRESSES: Information pertaining to this rulemaking action may be 
examined at the Federal Aviation Administration (FAA), Transport 
Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Hania Younis, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (206) 227-2764; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

[[Page 24326]]

Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes was published in the Federal 
Register on August 28, 1996 (61 FR 44243). That action proposed to 
require repetitive tests to verify the integrity of the yaw damper 
coupler, and various follow-on actions. That action also proposed to 
require a one-time inspection to determine the part number of the 
engage solenoid valve of the yaw damper, and replacement of the valve 
with a valve having a different part number, if necessary.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Request for Issuance of Two Separate AD's

    One commenter requests that the proposed rule, which proposed 
actions related to the yaw damper coupler/rate gyroscope and the engage 
solenoid valve of the yaw damper, be separated into two independent 
AD's--one for the yaw damper coupler/rate gyroscope, and the other for 
the engage solenoid valve. The commenter believes that the actions 
required for each of these parts are sufficiently different that 
recordkeeping requirements warrant separate rules.
    The FAA finds that issuance of two separate AD's is appropriate: 
one to address the yaw damper coupler/rate gyroscope, and another to 
address the engage solenoid valve. Therefore, this final rule is being 
issued to address actions associated with the engage solenoid valve of 
the yaw damper coupler. [Those actions appeared in paragraph (b) of the 
proposal.]
    Further, the FAA is considering the issuance of separate rulemaking 
action to require accomplishment of the actions contained in the 
proposal that address the yaw damper coupler/rate gyroscope. [Those 
actions appeared in paragraph (a) of the proposal.] Since the issuance 
of the proposal, the FAA has determined that the requirements contained 
in paragraph (a) must be expanded to require hard-time replacement of 
the rate gyroscope. That paragraph originally proposed to require, in 
part, replacement of the rate gyroscope only if necessary following 
testing.

Request To Withdraw the Proposal

    One commenter requests that the FAA withdraw the proposed rule. The 
commenter does not believe that the proposed requirement to replace the 
existing engage solenoid valve with one that uses encapsulated coils is 
warranted. The commenter states that industry experience with the 
existing engage solenoid valve indicates an extremely reliable valve. 
The commenter adds that the mean time between failures is in excess of 
150,000 flight hours. In addition, the commenter states that valves 
with encapsulated coils have been no more reliable than the existing 
valves. The commenter also states that failure of this valve is not a 
safety of flight issue.
    The FAA does not concur with the commenter's request to withdraw 
the proposal. The FAA has not received data that demonstrate the 
commenter's contentions concerning the reliability of the existing 
engage solenoid valve. Additionally, the FAA finds that failure of the 
existing valve could result in abrupt, uncommanded yawing of the 
airplane, which could result in reduced controllability of the 
airplane. This AD addresses that unsafe condition.

Request To Allow Option for Replacing Coils

    Another commenter requests that the proposal be revised to allow 
operators the option of changing the engage solenoid valve or replacing 
the soft-potted coils with encapsulated coils. The commenter asserts 
that this option will still accomplish the intent of the AD, and will 
give credit to operators that previously have upgraded to the 
encapsulated coils while maintaining the original valve part number. 
The commenter adds that this valve is used in multiple locations and on 
several fleets, and the introduction of a new and unique part number is 
undesirable.
    The FAA does not concur with the commenter's request to allow an 
option in this AD. The FAA points out that no new or unique part number 
is being introduced by this AD. The parts that are required to be 
installed by this final rule are currently optional parts that could 
have been installed prior to the issuance of this AD. The FAA 
acknowledges the commenter's concern regarding the use of the valve in 
multiple locations and on several fleets; however, the FAA has 
determined that issuance of this AD is necessary to address the 
identified unsafe condition. If an operator desires to replace the 
electric coil inside the valve with an encapsulated coil to bring the 
valve to the proper configuration, the FAA would consider a request for 
approval of an alternative method of compliance, in accordance with the 
provisions of this AD, provided that complete substantiating data are 
submitted.

Request for Replacement of Engage Solenoid Valve Based on Results of 
Dielectric Tests

    One commenter requests that the FAA eliminate the requirement to 
replace the engage solenoid valves, and require replacement of the 
valves only on the basis of results of dielectric tests. The commenter 
states that simple electrical test can be performed in-situ; the 
commenter believes this test can reveal dielectric breakdown prior to 
failure. The commenter concludes that such testing and a requirement to 
upgrade the engage solenoid valve (if degradation is detected) would be 
appropriate.
    The FAA does not concur. The FAA is unaware of a test procedure 
such as that suggested by the commenter. The FAA has been advised that 
data from the manufacturer shows that encapsulated coils provide higher 
reliability due to increased resistance to damage and moisture. The FAA 
finds that basing replacement only upon testing, as suggested by the 
commenter, would not prevent failures that could occur between 
maintenance checks. However, the FAA would consider a request for 
approval of an alternative method of compliance, in accordance with the 
provisions of this AD, provided that complete test procedures and 
substantiating data are submitted.

Request for Further Testing of Engage Solenoid Valve

    One commenter requests that further testing be accomplished on the 
engage solenoid valve having part number 10-60811-( ) to either develop 
a test for the internal corrosion or to key the valves so they are 
unique to the rudder PCU position. The commenter points out that this 
particular valve is installed in 12 to 16 locations on each airplane, 
and it would be very difficult to restrict acceptable part numbers to 
only the rudder PCU. The commenter also states that it would be costly 
if airlines are forced to change all of these valves to ensure that the 
wrong valve is not installed on the rudder PCU; if the design of the 
part was keyed such that the valve installed on the rudder PCU is 
unique, this cost could be avoided.
    The FAA does not concur with the commenter's request. While the FAA 
recognizes that some operators may elect to replace valves having the 
affected part number at all locations of the airplane, this AD requires 
replacement of the engage solenoid valve only in the rudder PCU, and 
not at all locations where that valve is installed. The FAA does not 
agree that an internal test for corrosion is necessary since the new 
replacement

[[Page 24327]]

valve is designed to preclude moisture penetration and consequent 
corrosion. While such a test may be desirable, the FAA is not aware of 
the availability of such a procedure. Should such a test be developed, 
the FAA would consider a request for approval of an alternative method 
of compliance in accordance with the provisions of this AD. The FAA 
finds that installation of these newly designed valves at the 
replacement interval specified in this AD will ensure an acceptable 
level of safety of the affected fleet.

Request for Revised Compliance Time for Replacement of Engage Solenoid 
Valve

    Several commenters request that the requirement for replacement of 
certain engage solenoid valves be revised from 18 months to the next 
PCU shop visit. The commenters contend that the proposed AD should not 
require hard-time replacement. One of these commenters states that past 
experience has revealed the reliability of engage solenoid valves 
having part numbers 10-60881-1, -3, and -9 has been very good; these 
valves have a mean time between failures of 130,000 flight hours.
    The FAA concurs that the proposed compliance time can be extended 
without compromising the safety of the affected fleet. In light of the 
information presented by the commenters, the FAA has revised the 
compliance time specified in paragraph (a) of this AD to within five 
years or 15,000 flight hours after the effective date of this AD, or at 
the next time the PCU is sent to a repair facility (whichever occurs 
first). This revised compliance time should allow the action to be 
performed at a base during regularly scheduled maintenance where 
special equipment and trained maintenance personnel will be available, 
if necessary.

Request for Reduced Compliance Time for Replacement of Engage Solenoid 
Valve

    One commenter supports the proposal, but requests that the proposed 
compliance time for one-time inspection of the engage solenoid valve be 
reduced from 18 months to 3 months to provide an acceptable level of 
safety.
    The FAA does not concur with the commenter's request to shorten the 
proposed compliance time. In developing the proposed compliance time, 
the FAA considered the safety implications, parts availability, and 
normal maintenance schedules for timely accomplishment of the required 
actions. In consideration of these factors, the FAA determined that the 
compliance time, as proposed, represents an appropriate time in which 
the one-time inspection can be accomplished in a timely manner within 
the fleet and still maintain an adequate level of safety. In fact, the 
FAA has determined, as discussed above, that the proposed compliance 
can be extended somewhat without compromising the safety of the fleet. 
Operators are always permitted to accomplish the requirements of an AD 
at a time earlier than that specified as the compliance time. If 
additional data are presented that would justify a shorter compliance 
time, the FAA may consider further rulemaking on this issue.

Request for Clarification of Part Numbers

    Two commenters request clarification of the part numbers (P/N) of 
the engage solenoid valve addressed in the proposal. One of these 
commenters, Boeing, indicates that there are two suppliers that have 
qualified parts to Boeing P/N 10-60811-3. Parker P/N 59600-5007 has a 
soft-potted coil (similar to P/N 10-60811-1 and -9), while Sterer P/N 
45080 has an encapsulated epoxy coil (similar to P/N 10-60811-8 and -
13). The second commenter states that the P/N's of the engage solenoid 
valve that appear in the proposed rule do not exist.
    The FAA agrees that clarification is necessary. The P/N's that 
appeared in paragraph (b) of the proposal were incorrect. Paragraph (a) 
of this final rule [which appeared as paragraph (b) of the proposal] 
has been revised to specify that the correct P/N's of the valves to be 
removed are Boeing P/N 10-60811-3 and Parker P/N 59600-5007 (Boeing P/N 
10-60811-3), and that the correct P/N's of the replacement valves are 
Boeing P/N 10-60811-8 and -13, and Sterer P/N 45080 (Boeing P/N 10-
60811-3).
    Operators should note that both the Parker and Sterer P/N's have 
the same Boeing P/N--10-60811-3. If, upon inspection, Boeing P/N 10-
60811-3 is found to be installed, operators must ascertain the vendor 
P/N. Parts having Boeing P/N 10-60811-3 and Parker P/N 59600-5007 must 
be replaced, and are not considered to be acceptable for use as 
replacement parts. The FAA has included a note in this final rule to 
reflect this information.

Request To Revise Reference to Maintenance Manual

    Boeing indicates that the appropriate reference for replacement of 
the engage solenoid valve, as specified in paragraph (b) of the 
proposal, is the Boeing Maintenance Manual 22-12-11. The proposal 
indicates that the appropriate reference is Chapter 27-20-01 of the 
Boeing 737 Overhaul Manual.
    The FAA concurs that the reference provided by the commenter is 
appropriate. The FAA has reviewed the references contained in both the 
maintenance and overhaul manuals. Both manuals provide procedures for 
installation of the part. However, the overhaul manual addresses 
procedures to be used when the PCU is not installed on the airplane; 
the maintenance manual provides not only those procedures, but 
additional information related to access and close-up of the airplane. 
The FAA concludes that the maintenance manual is the appropriate 
reference for purposes of this AD, and has revised the final rule 
accordingly.

Request To Revise Statement of Findings of Critical Design Review 
Team

    One commenter requests the second paragraph of the Discussion 
section that appeared in the preamble to the proposed rule be revised 
to accurately reflect the findings of the Critical Design Review (CDR) 
team. The commenter asks that the FAA delete the one sentence in that 
paragraph, which read: ``The recommendations of the team include 
various changes to the design of the flight control systems of these 
airplanes, as well as correction of certain design deficiencies.'' The 
commenter suggests that the following sentences should be added: ``The 
team did not find any design issues that could lead to a definite cause 
of the accidents that gave rise to this effort. The recommendations of 
the team include various changes to the design of the flight control 
systems of these airplanes, as well as incorporation of certain design 
improvements in order to enhance its already acceptable level of 
safety.''
    The FAA does not find that a revision to this final rule in the 
manner suggested by the commenter is necessary, since the Discussion 
section of a proposed rule does not reappear in a final rule. The FAA 
acknowledges that the CDR team did not find any design issue that could 
lead to a definite cause of the accidents that gave rise to this 
effort. However, as a result of having conducted the CDR of the flight 
control systems on Boeing Model 737 series airplanes, the team 
indicated that there are a number of recommendations that should be 
addressed by the FAA for each of the various models of the Model 737. 
In reviewing these recommendations, the FAA has concluded that they 
address unsafe conditions that must be corrected through the issuance 
of AD's. Therefore, the FAA does not concur that these

[[Page 24328]]

design changes merely ``enhance [the Model 737's] already acceptable 
level of safety.''

Conclusion

    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 
increase the economic burden on any operator nor increase the scope of 
the AD.

Cost Impact

    There are approximately 2,675 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 1,091 
airplanes of U.S. registry will be affected by this AD.
    The FAA estimates that it will take approximately 1 work hour per 
airplane to accomplish the required one-time inspection of the engage 
solenoid valve, at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of the required inspection on U.S. 
operators is estimated to be $65,460, or $60 per airplane.
    The cost impact figures discussed 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.
    Should an operator be required to replace an engage solenoid valve 
of the yaw damper, it will take approximately 3 work hours to 
accomplish the replacement, at an average labor rate of $60 per work 
hour. Required parts will cost approximately $1,688 per airplane. Based 
on these figures, the cost impact of any necessary replacement of an 
engage solenoid valve is estimated to be $1,868 per airplane.

Regulatory Impact

    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, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends 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:

97-09-15 Boeing: Amendment 39-10011. Docket 96-NM-151-AD.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 (b) 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 sudden uncommanded yawing of the airplane due to 
potential failures within the yaw damper system, and consequent 
injury to passengers and crewmembers, accomplish the following:
    (a) Perform a one-time inspection of the engage solenoid valve 
of the yaw damper to determine the part number (P/N) of the valve. 
If any valve having Boeing P/N 10-60811-1 or -9, or Parker P/N 
59600-5007 (Boeing   P/N 10-60811-3) is installed, prior to further 
flight, replace it with a valve having Boeing P/N 10-60811-8 or -13, 
or Sterer P/N 45080 (Boeing P/N 10-60811-3). Accomplish the actions 
in accordance with procedures specified in Chapter 22-12-11 of the 
Boeing Maintenance Manual. Accomplish the inspection at the earlier 
of the times specified in paragraphs (a)(1) and (a)(2) of this AD.
    (1) Within 5 years or 15,000 flight hours after the effective 
date of this AD, whichever occurs first.
    (2) At the next time the PCU is sent to a repair facility.

    Note 2: Boeing In-Service Activities Report 95-03-2725-10, dated 
February 16, 1995 (for Model 737-100 and -200 series airplanes), or 
95-04-2725-10, dated February 24, 1995 (for Model 737-300, -400, and 
-500 series airplanes), provide additional information concerning 
interchangeability of solenoid valve part numbers.
    Note 3: Operators should note that, as specified in paragraph 
(a) of this AD, both the Parker and Sterer P/N's have the same 
Boeing P/N (10-60811-3). If, upon inspection, Boeing P/N 10-60811-3 
is found to be installed, operators must ascertain the vendor P/N. 
Parts having Boeing P/N 10-60811-3 and Parker P/N 59600-5007 must be 
replaced and are not considered to be acceptable replacement parts.

    (b) 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 4: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (c) 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.
    (d) This amendment becomes effective on June 9, 1997.

    Issued in Renton, Washington, on April 24, 1997.
Neil D. Schalekamp,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-11201 Filed 5-2-97; 8:45 am]
BILLING CODE 4910-13-P