Federal Register: July 24, 1998 (Volume 63, Number 142)Proposed RulesPage 39765-39769From the Federal Register Online via GPO Access [wais.access.gpo.gov]

DOCID:fr24jy98-27

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

Docket No. 98-NM-163-ADRIN 2120-AA64

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

SUMMARY: This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 747 series airplanes. This proposal would require a one-time inspection to detect discrepancies of the center fuel tank, and corrective actions, if necessary; replacement of all components of the fuel quantity indicating system (FQIS) of the center tanks with new FQIS components; and replacement of the FQIS wiring with new wiring. For certain airplanes, this proposal also would require a one-time inspection to detect discrepancies of the FQIS, and corrective actions, if necessary; and installation of a flame arrestor in the scavenge pumps of the center fuel tank. This proposal is prompted by design review and testing results obtained in support of an accident investigation. The actions specified by the proposed AD are intended to prevent ignition sources and consequent fire/explosion in the center fuel tank.

DATES: Comments must be received by September 8, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 98-NM-163-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays.

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: Dionne Stanley, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2250; 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 notice may be changed in light of the comments received.

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 filedin the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: ``Comments to Docket Number 98-NM-163-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. 98-NM-163-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On July 17, 1996, a Boeing Model 747 series airplane was involved in an accident shortly after takeoff from John F. Kennedy International Airport in Jamaica, New York. In support of the subsequent accident investigation, the FAA has participated in design review and testing to determine possible sources of ignition in the center fuel tank. The cause of the accident has not yet been determined.

This design review has identified the need to detect any conditions of in-service deterioration of the wiring, bonding, tubing installations, and other component installations inside the center fuel tank. If such conditions are detected, repair of these discrepancies would reduce the likelihood of these components becoming in-tank ignition sources due to lightning strikes, static electricity, or electrical failures outside of the fuel tank.

In addition, investigation has revealed that the knurled terminal blocks on ``series 3'' (and earlier series) probes of the fuel quantity indication system (FQIS) on Model 747 series airplanes are subject to chafing against their

[Page 39766]connecting wires; this chafing could result in an ignition source in the center fuel tank. ``Series 4'' (and subsequent series) probes, in contrast, incorporate a smooth-surface terminal block, nylon wire clamps, and a protective shrink-wrapped coating on the wires. Installation of ``series 4'' (or subsequent series) probes would prevent a potential in-tank ignition source due to incorrect terminal block configuration and resultant chafing damage to the wiring.

The FAA's review of the design of the scavenge pump assembly of the Model 747 center fuel tank has identified its vulnerability to center fuel tank ignition as a result of a potential mechanical failure of the pump. This condition could cause a spark or flame front to emanate from the pump assembly, propagate through the pump inlet line, and ignite the fuel-air mixture inside the center fuel tank.

Further, the FAA has become aware of numerous FQIS probe failures and system reliability problems in military applications. Subsequent investigation of Model 747 FQIS wiring has revealed the presence of corrosion, in the form of copper sulfur residue, on the affected probes and silver-plated copper wiring. This corrosion of the commonly used silver-plated copper wire is attributed to sulfur compounds inherently present in aviation fuels, bacterial growth, and the polysulfide sealant used in fuel tanks. Testing has demonstrated the potential for arcing and incandescing of copper sulfur residues at a given voltage, which could create a possible ignition source in the center fuel tank. A hot short failure in the FQIS outside of the fuel tank, in conjunction with the latent condition of excessive copper sulfur residue on probes or wiring inside the tank, could cause arcing or high-temperature leakage paths in fuel tanks. By contrast, nickel- plated wires have been shown to exhibit little or no corrosion in this same environment.

The unsafe conditions associated with damage to the center fuel tank wiring and other components described above, if not corrected, could result in ignition sources and consequent fire/explosion in the center fuel tank.

Wing Fuel Tanks vs. Center Fuel Tanks

The actions identified by the FAA during the course of the ongoing accident investigation are part of continued activity to correct any design-or maintenance-related deficiencies in the Boeing 747 fuel tanks that may lead to the existence of an ignition source. This proposed AD focuses on the center fuel tanks only.

Over the past 30 years, the service history for turbine-powered transport airplanes, excluding those used in military combat, has shown that in-flight explosions in wing fuel tanks occurred mainly when wide- cut fuels or a mixture of wide-cut fuel and kerosene-type fuels were used. The FAA has considered several factors that may contribute to the significantly improved safety record of wing fuel tanks relative to center fuel tanks:

1. On average, wing tank temperatures are lower than those in the center tanks because wing tanks have no significant on-airplane heat sources located in or near them, and the top and bottom surfaces of the wing tanks cool quickly as the airplane climbs into colder air.

2. Except for immediately after landing, wing tanks usually contain a relatively large amount of fuel to act as a heat sink while the airplane is on the ground being heated by sunlight and ambient air, whereas center tanks are often empty or near empty on airplanes during operation; and

3. Wing tank fuel pumps are normally operated with their pump inlets covered with fuel, which ensures that the wing tank pumps are always fuel-cooled during operation and mechanical sparks or high metal temperatures at the impeller cannot ignite vapor in the fuel tank.

In general, the flammability of a fuel is dependent on the concentration of fuel/air mixture and the fuel temperature. As a function of temperature, the fuel/air mixture can be too lean for combustion (lower flammability limit) or too rich for combustion (upper flammability limit). For kerosene-type fuels such as Jet A, elevated fuel/air mixture temperatures increase the likelihood of the mixture being within the flammable range. Avoiding airplane operation with fuel temperatures in the flammable range reduces the fuel/air mixture's exposure to ignition in the presence of an ignition source.

The unique environmental and operational conditions and service history information of fuel tanks show that the risk of an in-flight explosion is lower in wing fuel tanks than in center fuel tanks. Therefore, the FAA is not proposing to include the wing fuel tanks in this rulemaking activity.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 747-28- 2205, Revision 1, dated April 16, 1998. This service bulletin describes procedures for a visual inspection to detect discrepancies (damage, disbonding, and incorrect installation) of the center fuel tank wiring and components; and corrective actions, if necessary. Corrective actions involve repair or replacement of discrepant parts with new or serviceable parts. In addition, this service bulletin describes procedures for an electrical bonding test of the center fuel tank components, and reworking of any component with bonding outside specified maximum resistance limits.

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-28A2208, dated May 14, 1998. This alert service bulletin describes procedures for:

<bullet> insulation resistance testing of the FQIS;

<bullet> visual inspection of the FQIS wiring and components to detect discrepancies (chafing damage to the wiring and incorrect configuration of the terminal blocks), and repair of discrepant components or replacement with new or serviceable components;

<bullet> replacement of ``series 3'' (or earlier series) FQIS probes with new ``series 4'' (or subsequent series) probes;

<bullet> retermination of the wires to the tank units and compensator, and replacement of FQIS wire bundle assemblies with new parts, if necessary;

<bullet> retesting (insulation resistance) of all components; and

<bullet> performing a system adjustment and a system operational test of the FQIS.

The FAA also has reviewed and approved Boeing Alert Service Bulletin 747-28A2210, dated May 14, 1998. This alert service bulletin describes procedures for installation of a flame arrestor in the inlet line of the scavenge pump of the center fuel tank.

FAA's Determinations

The FAA has examined the circumstances and reviewed all available information related to the accident and subsequent investigations. The FAA finds that, in addition to the actions specified in the service bulletins described previously, replacement of the Model 747 FQIS components (FQIS probes, compensator, and terminal strip) and wiring will reduce the risk of ignition in the center fuel tank, for the reasons described in the Discussion section above.

The FAA has determined that repeated entry into the fuel tank will increase the risk of damage to in-tank components and systems. Moreover, extensive time and effort are required to access, purge, and close the fuel tank to accomplish each action proposed by this AD. Therefore, the FAA proposes a compliance time of 24 months to allow operators to concurrently perform all of the proposed actions in order to reduce

[Page 39767]the risk of damage to the airplane from repeated entry. The proposed compliance time for accomplishment of the actions also would provide operators time for planning and scheduling, thus reducing the cost impact on the operators.

The FAA is currently considering separate rulemaking to address long-term maintenance issues.

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:

1. Performing a one-time visual inspection to detect damage, disbonding, and incorrect installation of the center fuel tank wiring and components; and repair or replacement, if necessary.

2. Performing an electrical bonding test of the center fuel tank components; and rework, if necessary.

3. For certain airplanes, performing an insulation resistance test of the FQIS and a one-time visual inspection to detect discrepancies of the FQIS; replacement of ``series 3'' (and earlier series) FQIS probes with new ``series 4'' (and subsequent series) FQIS probes; and corrective actions, if necessary.

4. Replacing all FQIS components (FQIS probes, compensator, and terminal strip) with new components.

5. Replacing silver-plated copper FQIS wiring with new nickel- plated copper FQIS wiring.

6. For certain airplanes, installing a flame arrestor into the inlet line of the scavenge pumps of the center fuel tank.

The actions are required to be accomplished in accordance with the service bulletins (described previously), the 747 Maintenance Manual, or a method approved by the FAA.

The proposed AD also would require that operators report inspection findings to the manufacturer.

Other Relevant Rulemaking

Other fuel tank ignition scenarios have been studied by the FAA and have resulted in rulemaking action.

On December 9, 1997, the FAA issued AD 97-26-07, amendment 39-10250 (62 FR 65352, December 12, 1997), applicable to Boeing Model 747 series airplanes, which superseded AD 96-26-06, amendment 39-9870 (62 FR 304, January 3, 1997). AD 97-26-07 requires repetitive inspections of the Teflon sleeves that protect wiring to the boost pumps on the outboard main tanks on all Boeing 747 series airplanes. The Teflon sleeves are intended to protect the main tank boost pump wiring from chafing damage caused by the wires rubbing against each other or against the metal conduit that encases the wiring routed through the fuel tank. Chafing of these wires could lead to electrical arcing, which could potentially cause ignition of flammable vapors within the outboard wing fuel tanks. Similar action was taken on Model 737 series airplanes by telegraphic AD 98-11-52, issued May 14, 1998. The FAA is currently reviewing other Boeing airplane models to determine whether similar action is warranted.

During the inspections required by AD 97-26-07, one operator discovered that the required Teflon sleeves were missing on one airplane. In response, on May 5, 1998, the FAA issued AD 98-10-10, amendment 39-10522 (63 FR 26063, May 12, 1998), to require all operators of Boeing 747 series airplanes to verify that the protective Teflon sleeves were installed on the main tank boost pump wiring. AD 98-10-10 requires any operator discovering the absence of any Teflon sleeve on an airplane to perform corrective action prior to further flight.

On November 26, 1997, the FAA issued a notice of proposed rulemaking (NPRM) (Docket 97-NM-272-AD) (62 FR 63624, December 1, 1997), applicable to all Boeing Model 747-100, -200, and -300 series airplanes. This NPRM proposed a modification of the FQIS to incorporate separation, shielding, and/or electrical transient suppression features to prevent electrical signals with excessive energy from entering the fuel tanks. This action is intended to preclude electrical energy needed to produce ignition from entering the fuel tanks and will preclude the development of an ignition source within the FQIS if damage to wiring, corrosion, or other failures were to occur. On April 14, 1998, the FAA issued a similar NPRM (Docket 98-NM-50-AD) (63 FR 19852, April 22, 1998), for Boeing Model 737 series airplanes. The FAA is currently reviewing other Boeing airplane models to determine whether similar action is warranted.

In addition, the FAA is addressing airplane fuel tank flammability issues with respect to the transport airplane fleet. On January 23, 1998, the FAA established an Aviation Rulemaking Advisory Committee (ARAC) working group on fuel tank flammability reduction with the publication of a Notice of New Task Assignment in the Federal Register. This notice gives the ARAC working group until July 23, 1998, to provide the FAA and Joint Aviation Authority (JAA) with a report outlining specific recommendations and proposed regulatory text that will eliminate or significantly reduce the hazards associated with explosive vapors in the fuel tanks of transport category airplanes.

As mentioned previously, the FAA also is considering rulemaking to require that each type certificate holder develop a fuel tank maintenance and inspection program, and that each operator have an FAA- approved fuel system maintenance program. That proposal also would require a review of the original certification compliance findings to revalidate that failures within the fuel system will not result in ignition sources.

Cost Impact

There are approximately 1,069 airplanes of the affected design in the worldwide fleet. The FAA estimates that 251 airplanes of U.S. registry would be affected by this proposed AD.

The FAA estimates that it would take approximately 40 work hours per airplane to purge, access, and close the center fuel tank, at an average labor rate of $60 per work hour. The cost impact on U.S. operators to purge, access, and close the fuel tank is estimated to be $2,400 per airplane.

The FAA estimates that the proposed inspection of the center fuel tank would be required to be accomplished on 251 airplanes. It would take approximately 56 work hours per airplane to accomplish the proposed inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of this proposed inspection on U.S. operators is estimated to be $843,360, or $3,360 per airplane.

The FAA estimates that the proposed FQIS inspection and system operational test, probe replacement, and insulation resistance test would be required to be accomplished on 202 airplanes. It would take approximately 60 work hours (maximum) per airplane to accomplish the proposed FQIS inspection, at an average labor rate of $60 per work hour. Required parts would cost approximately $30,000 per airplane (maximum). Based on these figures, the cost impact of this proposed inspection on U.S. operators is estimated to be a maximum of $6,787,200, or $33,600 per airplane.

The FAA estimates that the proposed installation of a flame arrestor would be required to be accomplished on 214 airplanes. It would take approximately 2 work hours per airplane to accomplish the proposed installation, at an average labor rate of $60 per work hour. Required parts would cost approximately $1,107 per airplane. Based on these figures, the cost impact of this proposed installation on U.S.

[Page 39768]operators is estimated to be $262,578, or $1,227 per airplane.

The FAA estimates that the proposed replacement of all FQIS components would be required to be accomplished on 251 airplanes. It would take approximately 24 work hours per airplane to accomplish the proposed replacement, at an average labor rate of $60 per work hour. Required parts would cost approximately $10,000 per airplane. Based on these figures, the cost impact of this proposed replacement on U.S. operators is estimated to be $2,871,440, or $11,440 per airplane.

The FAA estimates that the proposed replacement of the FQIS wiring would be required to be accomplished on 251 airplanes. It would take approximately 24 work hours per airplane to accomplish the proposed replacement, at an average labor rate of $60 per work hour. Required parts would cost approximately $10,000 per airplane. Based on these figures, the cost impact of this proposed replacement on U.S. operators is estimated to be $2,871,440, or $11,440 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 AD were not adopted.

Regulatory Impact

The regulations proposed herein would 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 proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

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 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 98-NM-163-AD.

Applicability: All Model 747 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 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 (g) 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 ignition sources and consequent fire/explosion in the center fuel tank, accomplish the following:

  (a) Within 24 months after the effective date of this AD, accomplish paragraphs (a)(1) and (a)(2), in accordance with Boeing Service Bulletin 747-28-2205, Revision 1, dated April 16, 1998.

  (1) Perform a visual inspection of the center fuel tank wiring and components to detect discrepancies (damage, disbonding, and incorrect installation). If any discrepancy is detected, prior to further flight, repair the discrepant component, or replace it with a new or serviceable component. And

  (2) Perform an electrical bonding test of the center fuel tank components. If any measured resistance exceeds the limit specified by Figure 1 of the service bulletin, prior to further flight, rework the discrepant component.

Note 2: Revision 1 of Boeing Service Bulletin 747-28-2205 provides two additional actions (inspection of the body fuel tank components and measurement of the ground resistance of the pressure switch case on the auxiliary power unit pump) that were not provided in the original version of this service bulletin. Inspections and testing accomplished prior to the effective date of this AD in accordance with Boeing Service Bulletin 747-28-2205, dated June 27, 1997, are considered acceptable for compliance with the applicable actions specified in this AD.

  (b) Within 24 months after the effective date of this AD, perform an insulation resistance test of the fuel quantity indication system (FQIS), visual inspection of the FQIS wiring and components to detect discrepancies (chafing damage to the wiring and incorrect configuration of the terminal blocks), replacement of ``series 3'' (or earlier series) FQIS probes with new ``series 4'' (or subsequent series) FQIS probes, and system adjustment and system operational test; as specified by paragraph (b)(1) or (b)(2) of this AD, as applicable; in accordance with Boeing Alert Service Bulletin 747-28A2208, dated May 14, 1998. If any discrepancy is detected, prior to further flight, perform corrective actions in accordance with the alert service bulletin.

  (1) For Groups 1 and 2 airplanes, as listed in the alert service bulletin: Accomplish the inspection, testing, and corrective actions, as applicable, in accordance with Figure 2 of the alert service bulletin.

  (2) For Groups 3 and 4 airplanes, as listed in the alert service bulletin: Accomplish the inspection, testing, and corrective actions, as applicable, in accordance with Figure 3 of the alert service bulletin.

  (c) At the applicable time specified in paragraph (c)(1) or (c)(2) of this AD, submit a report of the results of the inspections required by paragraphs (a) and (b) of this AD, as applicable, to the Manager, Airline Support, Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. The report must include the information specified in Boeing Service Bulletin 747-28-2205, Revision 1, dated April 16, 1998 [for paragraph (a) of this AD]; and Boeing Alert Service Bulletin 747-28A2208, dated May 14, 1998 [for paragraph (b) of this AD]. Information collection requirements contained in this regulation have been approved by the Office of Management and Budget (OMB) under the provisions of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control Number 2120-0056.

  (1) For airplanes on which the inspections required by paragraphs (a) and (b) of this AD, as applicable, are accomplished after the effective date of this AD: Submit the report within 10 days after performing the applicable inspection.

  (2) For airplanes on which the inspections required by paragraphs (a) and (b) of this AD, as applicable, have been accomplished prior to the effective date of this AD: Submit the report within 10 days after the effective date of this AD.

  (d) Within 20 years since date of manufacture, or within 24 months after the effective date of this AD, whichever occurs later: Replace all center fuel tank FQIS components (FQIS probes, compensator, and terminal strip) with new FQIS components, in accordance with the 747 Maintenance Manual, chapters 28-11-00, 28- 41-00, 28-41-01, 28-41-02, and 28-41-09.

[Page 39769]

  (e) Within 20 years since date of manufacture, or within 24 months after the effective date of this AD, whichever occurs later: Replace the silver-plated copper FQIS wiring of the center fuel tank with new nickel-plated copper FQIS wiring, in accordance with 747 Maintenance Manual, chapters 28-11-00, 28-41-00, 28-41-01, 28-41-02, and 28-41-09.

  (f) For airplanes having line positions 1 through 971 inclusive: Within 24 months after the effective date of this AD, install a flame arrestor in the inlet line of the electrical motor-operated scavenge pump of the center fuel tank, in accordance with Boeing Alert Service Bulletin 747-28A2210, dated May 14, 1998.

  (g) 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 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

  (h) 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 July 15, 1998. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

FR Doc. 98-19460Filed7-23-98; 8:45 amBILLING CODE 4910-13-U