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Safety Recommendation Details

Safety Recommendation A-96-175
Details
Synopsis: ON 7/17/96, ABOUT 2031 EASTERN DAYLIGHT TIME, A BOEING 747-131, N93-119, OPERATED AS TRANS WORLD AIRLINES FLIGHT 800 (TWA800), CRASHED INTO THE ATLANTIC OCEAN, ABOUT 8 MILES SOUTH OF EAST MORICHES, NEW YORK, AFTER TAKING OFF FROM JOHN F. KENNEDY INTERNATIONAL AIRPORT (JFK), JAMACIA, NEW YORK. ALL 230 PEOPLE ABOARD THE AIRPLANE WERE KILLED. THE AIRPLANE, WHICH WAS OPERATED UNDER TITLE 14 CODE OF FEDERAL REGULATIONS (CFR) PART 121, WAS BOUND FOR CHARLES DE GAULLE INTERNATIONAL AIRPORT (CDG), PARIS, FRANCE. THE FLIGHT DATA RECORDER (FDR) & COCKPIT VOICE RECORDER (CFR) ENDED SIMULTANEOUSLY, ABOUT 13 MINUTES AFTER TAKEOFF. EVIDENCE INDICATES THAT AS THE AIRPLANE WAS CLIMBING NEAR 13,800 FEET MEAN SEA LEVEL (MSL), AN IN-FLIGHT EXPLOSION OCCURRED IN THE CENTER WING FUEL TANK (CTW); THE CWT WAS NEARLY EMPTY.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: Require the development of & implementation of design or operational changes that will preclude the operation of transport-category airplanes with explosive fuel-air mixtures in the fuel tanks: (b) pending implementation of design modifications, require modifications in operational procedures to reduce the potential for explosive fuel-air mixtures in the fuel tanks of transport-category aircraft. In the B-747, consideration should be given to refueling the center wing fuel tank (CWT) before flight whenever possible from cooler ground fuel tanks, proper monitoring & management of the cwt fuel temperature, & maintaining an appropriate minimum fuel quantity in the CWT. (Urgent)
Original recommendation transmittal letter: PDF
Overall Status: Closed - Unacceptable Action
Mode: Aviation
Location: EAST MORICHES, NY, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA96MA070
Accident Reports: In-flight Breakup Over the Atlantic Ocean Trans World Airlines Flight 800, Boeing 747-141, N93119
Report #: AAR-00-03
Accident Date: 7/17/1996
Issue Date: 12/13/1996
Date Closed: 11/15/2005
Addressee(s) and Addressee Status: FAA (Closed - Unacceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 3/10/2006
Response: In an October 28, 2005, e-mail from Mr. Steven Wallace, Director of the FAA's Office of Accident Investigation, to Ms. Elaine Weinstein, Director of the Safety Board's Office of Safety Recommendations and Communications, the FAA shared the results of a survey taken by the Air Transport Association (ATA). In this survey, the ATA asked its member airlines about their policies and procedures regarding the use of ground-conditioned air (GCA). GCA is one of the possible short-term operational procedures requested in this safety recommendation for reducing the potential for explosive fuel-air mixtures. The Safety Board has reviewed the survey results. Although most airlines surveyed indicated that they had policies encouraging the use of GCA, its use was subject to availability. Many of the airlines noted that GCA is often unavailable or incapable of fully cooling the aircraft. While the use of GCA has reduced the potential for explosive fuel-air mixtures in some fuel tanks in certain cases, there remain other situations where routine airline operations result in explosive mixtures in fuel tanks. The FAA has indicated that it is not considering requiring or encouraging any other short-term operational procedure revisions to address this recommendation, which is now 9 years old. Consequently, at the November 15, 2005, Board meeting, Safety Recommendation A-96-175 was classified "Closed-Unacceptable Action."

From: NTSB
To: FAA
Date: 11/15/2005
Response: As part of its November 11, 2005 meeting addressing the Safety Board's Most Wanted List of safety improvements, the Board voted to reclassify this recommendation from "Open--Unacceptable Response" to "Closed--Unacceptable Response" based on the results of the FAA's survey on airline's use of ground-conditioned air in response to the recommendation on short-term solutions that can be implemented quickly, and the failure of the FAA to pursue any other short-term actions that can be implemented quickly.

From: FAA
To: NTSB
Date: 10/28/2005
Response: Letter Mail Controlled 11/1/2005 9:39:40 AM MC# 2050507: Office of Accident Investigation, email to Elaine Weinstein, Director, SRC, 10/28/05 It has been difficult for us to get complete and accurate information about the degree to which operators of aircraft with heated center wing tanks (HWCTs) are using ground conditioned air (GCA) and minimizing the use of air conditioning "packs" during ground operations. I wanted you have the latest information we have obtained from the ATA, which is contained in the two attachments. The first attachment is a letter outlining the results of a survey they did of their member airlines. It notes that while fuel conservation has historically provided an incentive to use GCA, many operators have specific policies motivated by the desire to reduce exposure to flammable conditions in fuel tanks. It also notes certain unique situations, such as short turn-around times, or all-cargo operations where passenger comfort is not a factor and a greater percentage of turnaround operations are at night. The second attachment is a spreadsheet summarizing survey results. This came after the letter, and I believe represents slightly later data than that described in the letter. I note that the letter mentions 14 passenger carriers responding, while the spreadsheet shows 15. Most of the airline policies described call for the use of GCA whenever it is available. One notes that they expect it to be universal through their system in early 2006, another sets it as the standard when temperatures are above 60 degrees F. While this survey covers the vast majority of the passenger-carrying fleet, it does not provide specific use figures showing the number or percentage of turn-around operations where GCA is providing a benefit. ATA is fully aware of this and is working to provide more complete data We are determined to obtain more complete and accurate data on the use of GCA. More importantly, we are committed to taking further steps to maximize the use of GCA where it provides a safety benefit, and will have a focused effort on this prior to the next warm-weather season. We anticipate the support of ATA in both of these efforts.

From: NTSB
To: FAA
Date: 7/12/2005
Response: In a letter to the Safety Board dated May 17, 2000, the FAA concluded that using ground-conditioned air instead of running the airplane's on-board air conditioning system on the ground to cool the airplane's cabin on days when the outside temperature is above 60 degrees Fahrenheit could reduce flammable fuel/air vapors in center wing tanks. Boeing issued a May 2000 service letter that recommended that operators use ground-conditioned air, and the FAA supplemented the Boeing letter with an information bulletin requesting that FAA inspectors encourage operators to follow this procedure. The FAA did not take any action to require compliance with this procedure. On June 14, 2004, staff from the FAA and the Safety Board met to discuss this recommendation. After this meeting, at the request of the Board, the FAA surveyed airlines to determine whether the use of ground-conditioned air had changed within the previous 5 to 7 years and what approximate percentage of daily flights used ground-conditioned air versus aircraft-supplied air conditioning during ground/gate operations. The FAA found that only one of the carriers in the survey, or 1.6 percent, had changed its procedures regarding the use of ground-conditioned air, while 85 percent had made no changes. For the remaining 13.4 percent of carriers surveyed, based on the type of aircraft in the airline's fleet, the questions were not relevant. The survey further found that 94 percent of daily airline flights do not use ground-conditioned air exclusively. The Safety Board is not aware of any other actions the FAA plans to take to address Safety Recommendation A-96-175, as we approach the ninth anniversary of the TWA 800 accident. Please inform us if any further short-term actions, which can be implemented quickly, are planned by the FAA. The Safety Board will review and evaluate activities associated with recommendations on the List of Most Wanted Safety Improvements at a meeting in November. Please provide a response in time to allow us to include it in our evaluations in preparation for the November meeting.

From: FAA
To: NTSB
Date: 2/1/2005
Response: In its 2/1/2005 annual report to Congress, Regulatory Status of the National Transportation Safety Board's "Most Wanted" Recommendations to the Department of Transportation, the DOT wrote:As an interim action to reduce the operation of transport-category airplanes with explosive fuel-air mixtures, the FAA recommended operators use ground air conditioning equipment instead of operating the airplane's air conditioning units while at a gate between flights. This recommendation was made after evaluating other possible interim actions, including requiring refueling the center wing tanks before flight. The FAA and industry determined refueling did not provide any significant flammability reduction. The FAA did not mandate the use of ground air conditioning because of the high cost associated with requiring that operators install ground conditioning units where they did not exist. This would have made it more dificult to mandate long-term inerting based flammability reduction when research demonstrated inerting was practical. In addition to this interim action, in 2001, for the first time, the FAA issued fuel tank flammability requirements for new designs. This 2001 requirement limited the flammability exposure for new fuels to an interim level based on an industry recommendation while fuel tank inerting research continued. In addition, in 2001, the FAA issued SFAR 88 to require that manufacturers review their fuel tank systems to determine potential arcs, sparks, or hot spots that could ignite fuel vapors. As a result of SFAR 88, the FAA has received and reviewed all system safety assessments required for submittal by aircraft manufacturers and identified the appropriate solution set to address unsafe conditions.

From: NTSB
To: FAA
Date: 11/9/2004
Response: As part of its November 9, 2004 meeting addressing the Safety Board's Most Wanted List of safety improvements, the Board voted to: 1.Reclassify A-96-175, which called for the FAA to make modifications in operational procedures to reduce the potential for explosive fuel-air mixtures in the fuel tanks of transport category aircraft from "Open-Acceptable Response" to "Open-Unacceptable Response."

From: NTSB
To: FAA
Date: 3/11/2003
Response: The FAA's last correspondence on these recommendations was dated May 17, 2000. On August 23, 2000, the Safety Board issued Aviation Accident Report: In-flight Breakup Over the Atlantic Ocean Trans World Airlines Flight 800 Boeing 747-141, N93119 near East Moriches, New York, July 17, 1996, AAR-00-03, the final report on the TWA 800 accident. In that report, the Board commented on the FAA's activities in response to these recommendations, noting with respect to Safety Recommendation A-96-175: In addition, the FAA indicated that it is evaluating the use of ground sources for conditioned air (instead of using the air conditioning packs) as an additional measure to reduce the flammability of CWTs in existing designs and the current fleet. According to the FAA, use of ground sources on days when the temperature exceeds 60° F would reduce the fleetwide flammability of CWTs from about 35 percent to about 25 percent. The FAA stated that a Boeing service letter (SL) recommends that operators use ground sources for conditioned air when available and practical and that it intends to encourage operators to follow this recommendation. The Safety Board is pleased by the significant reduction in flammability that can be achieved by using ground sources for conditioned air and notes that a requirement that such sources be used seems to be a logical step toward satisfying the intent of Safety Recommendation A-96-175. In the TWA 800 final report, the Board summarized its evaluation and classified these recommendations: Although the use of ground sources for conditioned air can provide meaningful short-term benefits, fuel tank inerting appears to be a more promising, near-term method that could even more dramatically reduce fuel tank flammability in the existing fleet. Thus, the Safety Board is pleased that the FAA has recently begun to aggressively study this method. The Board strongly encourages the FAA to consider a broader range of inerting technologies and expedite the pace of its research and rulemaking initiatives with regard to fuel tank inerting. However, based on the FAA's recent input to the Board, and pending additional expedited action with regard to fuel tank inerting, Safety Recommendations A-96-174 and -175 are classified "Open--Acceptable Response." Safety Board staff has been briefed by and has remained in regular contact with FAA staff regarding the promising results of the FAA's research and development activities related to fuel tank inerting, which is responsive to the intent of A-96-174. While implementation has great promise, it may require years of effort and may not be possible in some aircraft. The Safety Board is not aware of any activity that the FAA is taking related to requiring the use of ground sources for conditioned air or other activity to meet the intent of Safety Recommendation A-96-175. The Board notes that Safety Recommendation A-96-175 is an urgent recommendation, although it is now over 6 years old. The Safety Board would appreciate receiving an update from the FAA on current, planned, and completed activities being taken in response to Safety Recommendations A-96-174 and -175.

From: NTSB
To: FAA
Date: 8/23/2000
Response: A complete history of these recommendations is addressed in the Board's accident report adopted 8/23/00. The report is titled "Aircraft Accident Report--In-Flight Breakup Over the Atlantic Ocean Trans World Airlines Flight 800 Boeing 747-131, N93119 near East Moriches, NY, 7/17/96."

From: NTSB
To: FAA
Date: 8/3/2000
Response: The Safety Board is pleased that the FAA has recently begun to aggressively study this method. However, given that 3 1/2 years have passed since the Board recommended that the FAA give significant consideration to the issue of fuel tank inerting as a means of precluding the operation of transport-category airplanes with flammable vapors in the fuel tanks, and given the nature of the results that have been achieved by prior ARACs (particularly the FTHWG) 655 the Board is concerned that the FAA has chosen to address this issue by forming another ARAC working group to review and advise the FAA regarding the practicality of fuel tank inerting methods. The Board strongly encourages the FAA to consider a broader range of inerting technologies 656 and expedite the pace of its research and rulemaking initiatives with regard to fuel tank inerting. However, based on the FAA™s recent input to the Board, and pending additional expedited action with regard to fuel tank inerting, Safety Recommendations A-96-174 and -175 are classified "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 5/17/2000
Response: Letter Mail Controlled 05/18/2000 3:19:52 PM MC# 2000639: During the recent discussions with the Board's staff, it was proposed that the FAA reevaluate methods that could reduce the heating of CWT's that have air conditioning packs located below the CWT'S. One method discussed in the meeting was the use of ground sources of conditioned air instead of using the air conditioning packs. The FAA evaluated this proposal and determined that an operational procedure that recommends the use of ground-conditioned air, also called preconditioned air, instead of running the packs on the ground would provide reduction in the exposure of those CWT's to flammable vapors. The FAA has also determined that using ground-conditioned air would provide a greater reduction in flammability exposure than would modifying the fuel loading and management of the Boeing 747 so that cooler fuel would be added to the CWT before flight. In the July 1998 report of the ARAC FTHWG, it was estimated that CWT's on a large airplane with packs located below the CWT's would be flammable an average of 30 percent of the fleet operational time of the airplane. The FAA has performed a similar analysis that considered the results of fuel tank flammability research completed since the FTHWG issued its report. The FAA analysis estimates that the CWT's would be flammable approximately 35 percent of the fleet operational time. Using the same analysis techniques, the FAA estimates that using ground-conditioned air on hot days (greater than 60 degrees Fahrenheit) would reduce the exposure to approximately 25 percent. Modifying the fuel loading and management of the Boeing 747 so that cooler fuel would be added to the CWT, as suggested as a possibility by the Board, would result in less of a reduction of the exposure to approximately 30 percent. The FAA also analyzed a combination of both refueling the CWT,s and using ground-conditioned air. This combination did not result in any additional reduction in the flammability exposure when compared to using ground-conditioned air alone. The FAA has been working with industry representatives to establish a program that would recommend the use of ground-conditioned air for those airplanes with air conditioning packs located below CWT's whenever an adequate source of ground-conditioned air is available. Boeing issued a service letter on March 5, 2000, that would be sent to all operators of Boeing airplanes with air conditioning packs located below CWT'S. The service letter recommended that operators use ground-conditioned air when available and practical, when ambient ground temperatures are greater than 60 degrees Fahrenheit. Analysis has shown that using ground-conditioned air provides little or no reduction in CWT flammability, which is already low, when ambient temperatures are below 60 degrees Fahrenheit. The service letter also recommends that operators evaluate opening the air conditioning pack bay doors to provide additional ventilation. The FAA will supplement the Boeing letter with an information bulletin to FAA representatives assigned to each air carrier encouraging application of the Boeing service letter. In addition, each FAA representative will discuss the recommended practice with each operator. Operators have begun to install ground-conditioned air equipment at airport gates, and the recent increases in fuel prices should result in the installation of even more ground-conditioned air equipment. I believe that the FAA has met the full intent of this safety recommendation, and I consider the FAA's action to be completed.

From: FAA
To: NTSB
Date: 5/6/2000
Response: Letter Mail Controlled 05/12/2000 3:05:14 PM MC# 2000612

From: NTSB
To: FAA
Date: 3/24/2000
Response: Notation 7250: The National Transportation Safety Board has reviewed the Federal Aviation Administration’s (FAA) Notice of Proposed Rulemaking (NPRM), “Transport Airplane Fuel Tank System Design Review, Flammability Reduction, and Maintenance and Inspection Requirements,” which was published in 64 Federal Register 58644 on October 29, 1999. The NPRM indicates that the July 17, 1996, accident involving TWA flight 800 and the ensuing Safety Board Safety Recommendations (A-96-174 through -177 and A-98-34 through -39) have prompted the FAA to examine the underlying safety issues surrounding fuel tank explosions, the adequacy of the existing regulations, the service history of airplanes certificated to these regulations, and existing fuel system maintenance practices. The FAA proposes to amend the current regulations to address prevention of ignition sources and minimization of flammable vapors in fuel tanks in future airplane designs. The Board generally supports the proposed regulatory changes; however, as discussed below, the Board believes that the FAA needs to give further consideration to some associated issues. Prevention of Ignition Sources in Fuel Tanks The NPRM proposes a Special Federal Aviation Regulation (SFAR) that would require type certificate (TC) holders for transport airplanes and holders of supplemental type certificates (STC) that affect the airplane’s fuel system to conduct a safety review of the fuel tank system that is designed to show that fuel tank fires or explosions will not occur. Specifically, the TC or STC holder would be required to determine whether the design meets the existing requirements of 14 Code of Federal Regulations (CFR) Section 25.901 and the requirements of Section 25.981(a) and (b), which would include several provisions added by the NPRM. If the design does not meet these requirements, the SFAR would require the TC or STC holder to develop the necessary corrective design changes. Section 25.981 currently requires that “a safe margin” exist between the temperature at any place inside a fuel tank where fuel ignition is possible and the lowest expected autoignition temperature of the fuel in the fuel tank. The NPRM proposes to revise Section 25.981 so that subsection (a) would prohibit an ignition source from being present at any point in the fuel tank system “where catastrophic failure could occur due to ignition of fuel or vapors.” The new rule would require that this be shown by demonstrating (1) compliance with the existing requirement regarding autoignition temperature and (2) that an ignition source in the fuel tank system could not result from any single failure, from any single failure in combination with any latent failure condition not shown to be extremely remote, or from any combination of failures not shown to be extremely improbable. The revised Section 25.981 would also require, in subsection (b), that critical design configuration control limitations, inspections, or other procedures be established as necessary to prevent development of ignition sources. According to the NPRM, the design approval holder would be expected to do the following to comply with the SFAR: develop a failure modes and effects analysis (FMEA) for all components in the fuel tank system. Analysis of the FMEA would then be used to determine whether single failures, alone or in combination with foreseeable latent failures, could cause an ignition source to exist in a fuel tank. A subsequent quantitative fault tree analysis should then be developed to determine whether combinations of failures expected to occur in the life of the affected fleet could cause an ignition source to exist in a fuel system. The Safety Board identified numerous potential ignition hazards (including, but not limited to, aging components, contamination and corrosion of components, and sulfide deposits on components) during the TWA flight 800 investigation. The FAA states that its intention is that these failure conditions, and any other foreseeable failures, should be assumed when performing the FMEA analysis. The Safety Board generally supports the intent of the SFAR in requiring an FMEA analysis, but is concerned about the construction of the FMEAs, as well as the thoroughness and integrity of the data that will be used. Concerns about the construction and integrity of data were raised during a recent review of a proprietary fault tree analysis that a manufacturer developed in response to a Board request as part of the TWA flight 800 accident investigation. The fault tree analysis described various potential failures and combinations of events that could lead to the ignition of the center wing fuel tank. Because of concerns that arose during a review by the Safety Board of the original fault tree analysis and a subsequent revision, the Board requested that National Aeronautics and Space Administration (NASA) failure analysis specialists examine the document. A November 25, 1998, letter from Ms. Amanda H. Goodson, NASA’s Director for Safety and Mission Assurance, summarized the NASA review as follows: Many of the probabilities, failure rates, and/or exposure times were much lower than would reasonably be expected. The probability of occurrence should be higher and/or exposure times should be longer on many of the basic events….Based on our evaluation of the tree and the information provided by the NTSB, the subject fault tree analysis quantification cannot stand up to peer review and should not be viewed as realistic. It should be noted that the logic of the tree could not be fully evaluated since we did not have access to the engineering drawings and schematics of the system. However, based on previous systems experience, we would expect the tree to be constructed differently. The Safety Board’s concerns about the FMEAs are amplified by the fact that no single source exists for reliable and comprehensive data on component failures or malfunctions. Because the calculations in a FMEA are based on failure rates, incomplete or inappropriate failure data can skew the results of an examination. The Board is aware that service history data maintained by manufacturers do not capture data from all operators. Further, the Board has found that the amount of data provided by the manufacturers of replacement component parts sometimes greatly exceeds the data provided by the aircraft manufacturers (possibly because replacement parts suppliers can sell parts directly to operators and repair facilities). Although the FAA collects a significant amount of data about mechanical failures through its Service Difficulty Report (SDR) program, even these data are incomplete. Other sources of potentially relevant data are the service histories maintained by the military of its variants of commercial airliners and the Board’s accident and incident investigation database; however, neither of these sources provides complete data either. Further, the many affected TC and STC holders (some of which are not the original designers or manufacturers) may have varying levels of experience with developing FMEAs. In addition, the Safety Board is concerned that engineers working for TC and STC holders may not recognize the existence or significance of certain hazards and that potentially competing interests may affect the quality and thoroughness of some FMEAs. In cases in which the TC or STC holder no longer exists, FAA personnel with varying levels of skill and experience may have to conduct the FMEAs. Finally, the Safety Board is concerned that the FAA may have an insufficient number of staff who are trained to properly evaluate an FMEA. Therefore, to ensure the integrity and effectiveness of the fuel tank system safety review, the Safety Board urges the FAA to develop and provide adequate standards and criteria to guide the development of the FMEAs and fault tree analyses. In particular, because there is no single comprehensive collection system that contains data on the failure of airplane components and because of the inadequacies that exist in each source of data, those guidelines should specify that the data used for the FMEAs must be collected from all available sources, including operators, manufacturers, and appropriate government agencies. The FAA needs to provide adequate oversight and auditing of the FMEA analysis results to ensure their technical accuracy and integrity. In particular, such oversight and auditing should include a review of the data sources used to ensure that all available and appropriate sources of failure data have been taken into account. FAA oversight and auditing can also provide a method to identify potential deficiencies in the FMEAs that might not be recognized by engineers and designated engineering representatives who work with these systems on a daily basis. The SFAR would also require TC and STC holders to develop all maintenance and inspection instructions necessary to maintain the design features required to preclude the existence or development of an ignition source within the fuel tank system. The Safety Board strongly endorses continuing airworthiness through improvements to maintenance, inspection, and minimum equipment lists. However, given the very general nature of some current inspection criteria pertaining to fuel tank safety (as documented by the FAA in its Transport Non-Structural Systems Plan), the Board is concerned that the instructions resulting from the SFAR requirement may be similarly broad and, therefore, potentially ineffective. Many potential ignition sources (such as hidden cracks in wiring, sulfide deposits, and use of inappropriate materials) may not be apparent during a general visual inspection. Therefore, the Board urges the FAA to ensure that the maintenance and inspection instructions developed as a result of this SFAR are detailed and specific enough to provide mechanics with useful inspection criteria and to ensure that they are properly trained about how to effectively carry out those instructions, including a requirement for a detailed inspection of each component in any area that may be exposed to fuel or fuel vapors. Minimizing Development of Flammable Vapors in Fuel Tanks The NPRM also proposes to add a new subsection (c) to 14 CFR Section 25.981, which would require that fuel tank installations in newly designed airplanes include a means to minimize the development of flammable vapors in fuel tanks, or to mitigate the effects of an ignition of fuel vapors within the fuel tanks, such that no damage caused by an ignition will prevent continued safe flight and landing. (Examples of means by which such mitigation could be accomplished, and which are being actively studied, are installation of fire suppressing polyurethane foam to extinguish or retard ignition of fuel vapor and installation of explosion suppression systems. The Safety Board notes that there are numerous unresolved operational and maintenance problems inherent in such in-tank mitigation technologies. In light of the FAA’s limited resources, the Safety Board urges the FAA to attempt to realize more immediate and effective safety improvements by focusing its resources on methods for minimizing the development of flammable vapors, rather than means for mitigating the effects of ignition.) The FAA acknowledges that this proposal is not intended to prevent the development of flammable vapors because total prevention has not been found to be feasible. Rather, the FAA states that the proposal is intended as an interim measure to preclude, in new designs, the use of design methods that result in a relatively high likelihood that flammable vapors will develop in fuel tanks. The Safety Board is pleased that the FAA has recognized that minimizing the development of flammable fuel vapors in fuel tanks is necessary to reduce the risk of fuel tank explosions and supports the proposed changes to 14 CFR Section 25.981. Further, the Board understands that this is an interim measure and looks forward to receiving further information from the FAA once it completes its evaluation of and research into means for minimizing the development of flammable vapors within fuel tanks and develops a definitive standard to address this issue in new designs. However, the Safety Board is concerned that the NPRM does not propose any regulatory changes that address fuel tank flammability in current designs and in the existing fleet. This is especially disturbing because some operational measures (such as limiting the on-ground operating time of air conditioning packs and substituting a ground-based cool air supply and cooling or ventilating the pack bay) that can reduce current levels of flammable vapors could be accomplished immediately. The Board is also aware that the FAA is conducting research into on-ground fuel tank inerting systems for the existing fleet. Because the Board believes that fuel tank inerting is a promising, near-term method that could dramatically reduce fuel tank flammability in the existing fleet, it strongly supports the FAA’s continued work in this regard and looks forward to regulatory implementation. In the NPRM, the FAA discussed the conclusions of the Aviation Rulemaking Advisory Committee’s (ARAC) Fuel Tank Harmonization Working Group (FTHWG), which was established on January 23, 1998, to evaluate methods to reduce or eliminate hazards associated with explosive vapors in fuel tanks. The FTHWG concluded that the safety record of fuel tanks located in the wings (which the FTHWG calculated were flammable about 7 percent of the fleet operational time) was adequate and that if the same level of safety could be achieved in center wing fuel tanks the overall safety objective could be achieved. Thus, the FTHWG proposed limiting the airplane’s exposure to flammable conditions in all fuel tanks to less than 7 percent of the expected fleet operational time. Although FAA staff have indicated to Safety Board staff that the FAA does not intend to endorse the FTHWG’s proposed exposure criteria, the Board nonetheless wishes to register its concerns about those criteria. Because it is a fleetwide average, it does not account for increased risks that may exist at specific locations, during certain time periods, or for certain flights. In addition, the premise that transport airplane fuel tanks located in the wings have an acceptable safety record is unacceptable because wing fuel tanks have exploded. The Safety Board believes that the goal should be to completely eliminate the development of flammable vapors in fuel tanks to the greatest extent technically feasible (such as would result from the use of on-ground inerting systems). The Safety Board appreciates the opportunity to comment on this proposed rulemaking.

From: FAA
To: NTSB
Date: 11/3/1999
Response: Letter Mail Controlled 11/05/1999 12:48:36 PM MC# 991232: The FAA has reevaluated its response to this safety recommendation according to the action plan described in its letter dated March 3, 1998. Additional analysis and a review of available jet fuel data have been performed since March 1998. A team of fuel experts was established by the FAA and included a representative of the FAA, the Board, the National Aeronautics and Space Administration (NASA), and several recognized independent jet fuel experts. The team reviewed all available past data on the relationship of fuel temperature to minimum required ignition energy and reviewed new data developed by Dr. Shepherd of the California Institute of Technology under contract to the Board. A report containing the team's conclusions and recommendations of the data to be used in FAA's decision making was issued in June 1998. The team reviewed all available reports on the subject of Jet A fuel flammability. The review included jet fuel definitions and specifications, jet fuel flammability data, the influences of various factors on fuel flammability, and predictive analyses and models for determining when a fuel tank vapor mixture is flammable. The team reached several conclusions regarding the flammability of Jet A fuel, which are contained in the report. (The full report is available on Internet through the FAA Technical Center, Fire and Cabin Safety web site, at http://www.fire.tc.faa.gov by selecting "REPORTS" from this web site.) The report includes the following conclusion on adding fuel to center wing tanks to reduce the exposure of the tank to flammable vapors: "At the present time, there are neither flight data nor thermal models or calculations that are adequate to determine the extent of the fuel temperature variation over typical flight profiles for various fuel loading scenarios, hence, the times of exposure and probabilities of experiencing potentially hazardous conditions cannot be determined. Therefore, the effectiveness of additional fuel being added to a fuel tank cannot be determined." The ARAC Fuel Tank Harmonization Working Group also evaluated the effects of loading fuel into an otherwise empty center wing tank with heat sources like air conditioning packs located below the tank. The ARAC report concluded that loading such a center tank to 10 percent to 15 percent of its capacity prior to takeoff would only provide a small reduction in the exposure of the tank to flammable vapors. The reduction in the flammability exposure would be produced by limiting the heating effects of air conditioning packs, but would not eliminate the exposure of the tank to flammable vapors. The ARAC working group performed a thermal analysis of a generic model of a large airplane with center wing tanks with air conditioning packs located below the tank. In the model, the center tank was loaded from 10 percent to 15 percent of its capacity before takeoff, and then the fuel was used during the flight. The ARAC working group's analysis predicted that the fleet average exposure to flammable vapors would be reduced from 27 percent with the existing type operations to 20 percent with a requirement to always load center tank fuel. The FAA has concluded that, based on the independent review of available jet fuel data and the additional analysis performed since March 1998, the information available still shows that there is not a significant safety improvement from adding fuel to the center wing tank of a Boeing 747 airplane. The FAA is conducting additional research into the properties of Jet A fuel and the flammability of transport airplane fuel tanks as described in the enclosure. The FAA will reevaluate this safety recommendation if the results of these or other activities indicate that significant reductions in the flammability of fuel tanks can be obtained by loading fuel in center wing tanks. The FAA is continuing to take short-term actions to reduce the likelihood of fuel tank explosions by proposing airworthiness actions to correct any design or maintenance-related deficiencies in transport airplanes, fuel tank systems that may lead to an ignition source being present. The FAA will continue to propose airworthiness actions to eliminate any specific conditions that could result in ignition sources within the fuel tanks. Since the TWA 800 accident, the FAA has issued 23 airworthiness directives (AD) and proposed four additional AD's that address fuel tank safety issues. The FAA has also initiated studies and research regarding fuel tank flammability reduction. A listing of these actions is included in the enclosed chart. I believe that the FAA has met the full intent of this safety recommendation, and I consider the FAA's action to be completed.

From: NTSB
To: FAA
Date: 9/21/1999
Response: ALTHOUGH THE SAFETY BOARD SUPPORTS THE INCREASED INSPECTIONS OF WIRING AND FUEL TANKS, THE BOARD BELIEVES STRONGLY, ESPECIALLY IN LIGHT OF THE FLIGHT TEST RESULTS, THAT OPERATIONAL PROCEDURES IN REFUELING MUST BE CHANGED TO PROVIDE THE HIGHEST LEVEL OF SAFETY. BECAUSE THE FAA HAS NOT TAKEN ANY ACTION DIRECTLY RESPONDING TO A-96-175 IN NEARLY 3 YEARS, IT IS CLASSIFIED "OPEN--UNACCEPTABLE RESPONSE." THE SAFETY BOARD REQUESTS THAT THE FAA PROVIDE ANY ADDITIONAL INFORMATION IT DEEMS PERTINENT REGARDING THIS RECOMMENDATION.

From: FAA
To: NTSB
Date: 3/3/1998
Response: Letter Mail Controlled 3/5/98 4:04:27 PM MC# 980293 ON 12/3/97, THE FAA STATED THAT, BASED ON THE INFORMATION AVAILABLE AT THE TIME, IT DID NOT SEE A SIGNIFICANT SAFETY BENEFIT FROM ADDING FUEL TO THE CENTER TANK WHEN IT WOULD NORMALLY BE EMPTY. HOWEVER, AS DISCUSSED IN THE DECEMBER PUBLIC HEARING, THE FAA IS REEVALUATING ITS RESPONSE TO THIS RECOMMENDATION. TESTING CONDUCTED UNDER THE BOARD'S CONTRACT BY DR. JOSEPH SHEPHERD OF THE CALIFORNIA INSTITUTE OF TECHNOLOGY INDICATES THAT REDUCING THE TEMPERATURE OF THE FUEL IN THE CENTER WING FUEL TANK SIGNIFICANTLY INCREASES THE ENERGY LEVEL NEEDED TO CAUSE IGNITION OF THE FUEL. THIS NEW INFORMATION CONFLICTS WITH INDUSTRY STANDARD DATA THAT HAVE BEEN USED BY THE MILITARY AND FAA IN ESTABLISHING THE FLAMMABILITY OF VAPORS WITHIN FUEL TANKS. THE FAA NEEDS TO UNDERSTAND THIS NEW INFORMATION. CONSEQUENTLY, THE FAA ESTABLISHED A TEAM OF FUEL EXPERTS TO REVIEW ALL AVAILABLE PAST DATA ON THE RELATIONSHIP OF FUEL TEMPERATURE TO MINIMUM REQUIRED IGNITION ENERGY AND TO REVIEW NEW DATA DEVELOPED BY DR. SHEPHERD. DR. MERRITT BIRKY OF YOUR STAFF IS SUPPORTING THE FAA IN THIS EFFORT. A REPORT CONTAINING THE TEAM'S CONCLUSIONS AND RECOMMENDATIONS OF THE APPROPRIATED DATA TO BE USED IN FAA'S DECISION MAKING IS EXPECTED TO BE COMPLETED BY THE END OF MARCH 1998. THE FAA WILL REVIEW THE TEAM'S RECOMMENDATIONS AND RE-EVALUATE WHETHER A SIGNIFICANT SAFETY IMPROVEMENT CAN BE ACHIEVED THROUGH PRACTICAL CHANGES IN FUEL LOADING AND FUEL USAGE PROCEDURES. IF ACCEPTABLE PROCEDURES CAN BE DEFINED, THE FAA WILL CONSIDER RULEMAKING TO REQUIRE SUCH PROCEDURES ON APPROPRIATE AIRPLANE MODELS. TO FACILITATE THIS PROCESS, I ASK THAT THE BOARD PROVIDE THE FAA WITH ALL DATA OBTAINED FROM THE TESTS CONDUCTED ON THE EVERGREEN AIRPLANE IN JULY 1997. IN THE FAA'S LETTER OF 12/3/97, SHORT-TERM ACTIONS WERE DESCRIBED TO REDUCE THE LIKELIHOOD OF FUEL TANK EXPLOSIONS. THOSE ACTIONS AND THE CURRENT STATUS ARE AS FOLLOWS: PROPOSING AIRWORTHINESS ACTIONS APPLICABLE TO THE BOEING 747 AIRPLANE TO REQUIRE PERIODIC INSPECTIONS OF THE FUEL TANKS AND EQUIPMENT INSTALLED IN THE FUEL TANKS. THE INSPECTIONS ARE INTENDED TO DETECT AND CORRECT ANY ANOMALOUS CONDITIONS WITHIN THE FUEL TANK, WIRING, AND PLUMBING THAT COULD LEAD TO THE IGNITION OF FLAMMABLE VAPOR. STATUS: THE FAA IS WORKING WITH BOEING ON REVISIONS TO BOEING SERVICE BULLETIN 747-28-2205, WHICH WAS ORIGINALLY RELEASED IN JUNE 1997. REVISIONS TO THE BULLETIN WILL ADDRESS ADDITIONAL AREAS THAT NEED TO BE INSPECTED, SUCH AS FUEL QUANTITY INDICATING SYSTEM WIRING, BASED ON REPORTS FROM INITIAL AIRPLANE INSPECTIONS. THE SERVICE BULLETIN REVISIONS ARE EXPECTED TO BE ISSUED BY MARCH 1998. THE FAA WILL ISSUE A NOTICE OF PROPOSED RULEMAKING (NPRM) WITHIN 90 DAYS AFTER THE SERVICE BULLETIN IS ISSUED. THE NPRM WILL PROPOSE THE ISSUANCE OF AN AIRWORTHINESS DIRECTIVE (AD) TO REQUIRE OPERATORS TO PERFORM THE INSPECTIONS DESCRIBED IN THE REVISED SERVICE BULLETIN. CONTINUING ACTIVITY TO CORRECT ANY DESIGN OR MAINTENANCE-RELATED DEFICIENCIES IN THE BOEING 747 FUEL TANKS THAT MAY LEAD TO AN IGNITION SOURCE BEING PRESENT. THE FAA WILL PROPOSE AIRWORTHINESS ACTIONS TO ELIMINATE ANY SPECIFIC CONDITIONS FOUND AS A RESULT OF THE ONGOING ACCIDENT INVESTIGATION THAT COULD RESULT IN IGNITION SOURCES WITHIN THE FUEL TANKS ON THE BOEING 747. STATUS: THE FAA HAS ISSUED OR IS ISSUING AD'S REQUIRING THE FOLLOWING: 1. ISSUED AD 97-26-07 EFFECTIVE 12/29/97, TO SUPERSEDE AD 96-26-06 TO REQUIRE A REPETITIVE INSPECTION OF TEFLON SLEEVES THAT PROTECT WIRING TO THE OUTBOARD MAIN TANK BOOST PUMPS ON ALL BOEING 747 SERIES AIRPLANES. SIMILAR AD ACTION IS PLANNED FOR THE BOEING 767 SERIES AIRPLANES. BOEING IS IN THE PROCESS OF PREPARING A SERVICE BULLETIN FOR THE BOEING 767 TO SUPPORT THE PLANNED AD. 2. ISSUED NPRM 97-NM-272-AD ON 11/26/97, PROPOSING AN AD TO REQUIRE MODIFICATION OF THE BOEING 747 FUEL QUALITY INDICATING SYSTEM WIRING TO INCORPORATE SEPARATION, SHIELDING, AND/OR ELECTRICAL TRANSIENT SUPPRESSION FEATURES TO PREVENT ELECTRICAL SIGNALS WITH EXCESSIVE ENERGY FROM ENTERING THE FUEL TANKS. A SIMILAR NPRM FOR THE BOEING 737 SERIES AIRPLANES IS BEING DEVELOPED AND IS EXPECTED TO BE ISSUED IN MARCH 1998. THE FAA IS CURRENTLY REVIEWING OTHER BOEING AIRPLANE MODELS TO DETERMINE WHETHER SIMILAR ACTION IS WARRANTED. 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 FUEL QUANTITY INDICATING SYSTEM IF DAMAGE TO WIRING, CORROSION, OR OTHER FAILURES WERE TO OCCUR. 3. THE FAA PLANS TO ISSUE AN NPRM PROPOSING AN AD TO REQUIRE THE REPLACEMENT OF CERTAIN FUEL QUANTITY INDICATING SYSTEM TANK UNITS ON EARLY BOEING 747 SERIES AIRPLANES. THOSE TANK UNITS, WHICH WERE REFERRED TO AS "SERIES 3 PROBES" AT THE HEARING, WERE FOUND BY THE BOARD TO HAVE CAUSED WIRE DAMAGE IN THE CONNECTING HARNESSES ON SOME AIRPLANES. BOEING IS PREPARING A SERVICE BULLETIN TO PROVIDE PROCEDURES FOR REPLACING SERIES 3 PROBES WITH PROBES OF AN IMPROVED DESIGN. THE BULLETIN IS EXPECTED TO BE COMPLETED BY MARCH 1998. THE FAA WILL ISSUE AN NPRM AD TO REQUIRE INCORPORATION OF THE SERVICE BULLETIN WITHIN 90 DAYS AFTER THE BULLETIN IS ISSUED. 4. THE FAA PLANS TO ISSUE AN NPRM PROPOSING AN AD TO REQUIRE THE INSTALLATION OF A FLAME ARRESTOR IN THE CENTER TANK SCAVENGE PUMP INLET LINE ON BOEING 747 SERIES AIRPLANES THAT ARE EQUIPPED WITH ELECTRIC MOTOR-DRIVEN SCAVENGE PUMPS. BOEING IS PREPARING A SERVICE BULLETIN TO ADDRESS THIS ISSUE AND ANTICIPATES ISSUANCE OF THE BULLETIN BY MARCH 1998. THE FAA WILL ISSUE A NPRM PROPOSING AN AD TO REQUIRE INCORPORATION OF THE SERVICE BULLETIN WITHIN 90 DAYS AFTER THE BULLETIN IS ISSUED. THE FAA IS DEVELOPING AN NPRM PROPOSING A SPECIAL FEDERAL AVIATION REGULATION (SFAR) APPLICABLE TO THE LARGE TRANSPORT AIRPLANE FLEET TO: 1. REQUIRE EACH TYPE CERTIFICATE HOLDER TO DEVELOP A FUEL TANK MAINTENANCE AND INSPECTION PROGRAM; 2. REQUIRE EACH OPERATOR TO HAVE AN FAA-APPROVED FUEL SYSTEM MAINTENANCE PROGRAM; 3. REQUIRE REVIEW OF THE ORIGINAL CERTIFICATION COMPLIANCE FINDINGS TO 14 CFR 25.903 AND 25.981 TO REVALIDATE THAT FAILURES WITHIN THE FUEL SYSTEM WILL NOT RESULT IN IGNITION SOURCES; AND 4. REQUIRE PROCEDURAL CHANGES TO PREVENT THE OPERATION OF ANY ELECTRICALLY DRIVEN FUEL PUMP IN FUEL TANKS WITH ADJACENT HEAT SOURCES WHEN THE PUMP'S INLET IS NOT FULLY SUBMERGED IN LIQUID FUEL. A FLAME ARRESTOR INSTALLED IN THE FUEL PUMP INLET LINE WOULD BE CONSIDERED AN ALTERNATE MEANS OF COMPLIANCE. THIS ACTION IS AN INTERIM ACTION INTENDED TO PREVENT MECHANICAL PUMP FAILURES FROM IGNITING VAPORS IN THE TANK VIA THE INLET LINE UNTIL THE FUEL PUMP DESIGN HAS BEEN REVALIDATED UNDER ITEM 3 ABOVE. STATUS: THE PROPOSED SFAR WILL BE PUBLISHED CONCURRENT WITH THE ARAC ACTIVITY. WE EXPECT TO COMPLETE OUR ACTION ON THIS NOTICE BY 9/30/98. IN SUMMARY, THE FAA IS TAKING ACTION TO PRECLUDE IGNITION SOURCES FROM BEING PRESENT IN OR DEVELOPING IN TRANSPORT AIRPLANE FUEL TANKS. IN ADDITION, THE FAA HAS TASKED A TEAM OF INDUSTRY EXPERTS TO DEVELOP NEW REGULATORY TEXT THAT WILL ELIMINATE OR SIGNIFICANTLY REDUCE THE PRESENCE OF FLAMMABLE FUEL VAPORS WITHIN FUEL TANKS OF NEW, CURRENT PRODUCTION, AND IN-SERVICE AIRPLANES. THE FAA WILL DETERMINE IF FUTURE ACTION IS WARRANTED TO IMPLEMENT A-96-175 TO REQUIRE MODIFIED FUEL LOADING AND MANAGEMENT PROCEDURES FOLLOWING RELEASE OF CONCLUSIONS FROM THE GROUP EVALUATING DR. SHEPHERD'S FINDINGS.

From: FAA
To: NTSB
Date: 12/3/1997
Response: Letter Mail Controlled 3/18/98 4:46:08 PM MC# 971618: This safety recommendation proposes short-term actions that are intended to reduce the potential of a fuel tank explosion by reducing the exposure of operating with explosive fuel-air mixtures in fuel tanks of transport category airplanes. Information received in response to the notice dated April 3, 1997, and the results from the recent National Transportation Safety Board-sponsored flight testing on the leased Evergreen Airways Boeing 747 indicate that there is a benefit to adding fuel to the center fuel tank for use early in the flight. However, an explosive fuel-air mixture would still exist for the remainder of the flight, effectively shifting the potential risk of explosion to a different segment of the flight. The effect each of the recommended actions would have on center wing tank fuel temperatures for a typical flight are shown on the enclosed plot. The plot of center wing tank fuel temperature versus flight time are predicted values generated from a thermal model developed by Boeing based on the recent flight testing on the Evergreen Airways Boeing 747. The plot also shows the effect of each of the Board safety recommendations on fuel temperatures. This analysis of the heat transfer characteristics of fuel tanks with adjacent heat sources shows that constant heating of the fuel within the center wing tank by the Environmental Control System equipment located below the tank results in operation much of the time with explosive mixtures in the tank. The Environmental Control System packs generate a large amount of heat that results in heating of fuel placed in the center wing tank such that loading of cool fuel into the tank and controlling use of air conditioning packs on the ground have little effect on overall exposure to operation with explosive fuel-air mixtures in the tank ullage space. The overall safety benefit that is produced by adding fuel to the center fuel tank for a typical flight is highly dependent on an accurate understanding of Jet A fuel properties and how Jet A behaves in both static and turbulent sloshing conditions. The FAA applauds the action of the Board to study further the properties of Jet A fuel. The work done in the investigation so far, and the Board's ongoing California Institute of Technology studies are essential steps to reach the definitive conclusions we both seek. The FAA is working closely with the Board on these initiatives. The FAA does not now see a significant safety benefit from adding fuel to the center fuel tank when it would normally be empty, but the FAA is open to any future findings coming from the Board's accident investigation. Removal of heat from the Environmental Control System bay or space between the packs and the tank via dedicated ventilation, coupled with incorporation of Safety Recommendation A-96-174 to insulate the tank from heat sources, may significantly reduce the exposure to operation with explosive mixtures in the fuel tank. However, development of the design modifications to achieve a significant reduction in overall exposure to operation with explosive fuel air mixtures (such as insulating the tank or inerting) is a long-term solution that will be evaluated by the ARAC in response to Safety Recommendation A-96-174. In the short term, the FAA will further reduce the likelihood of fuel tank explosions by: * Proposing airworthiness actions applicable to the Boeing 747 airplane to require periodic inspections of the fuel tanks and equipment installed in the fuel tanks. The inspections are intended to detect and correct any anomalous conditions within the fuel tank, wiring, and plumbing that could lead to the ignition of flammable vapor. * Continuing activity to correct any design or maintenance-related deficiencies in the Boeing 747 fuel tanks that may lead to an ignition source being present. The FAA will propose airworthiness actions to eliminate any specific conditions found as a result of the ongoing accident investigation that could result in ignition sources within the fuel tanks on the Boeing 747. The FAA will provide a status of its review by December 30, 1997, as we wish to consider the material from the Board's public hearing in December. * Proposing airworthiness actions applicable to the fleet of large transport airplanes to: 1. require each type certificate holder to develop a fuel tank maintenance and inspection program; 2. require each operator to have an FAA-approved fuel system maintenance program; 3. require review of the original certification compliance findings to 14 CFR 25.903 and 25.981 to revalidate that failures within the fuel system will not result in ignition sources; and 4. require procedural changes to prevent the operation of any electrically driven fuel pump in fuel tanks with adjacent heat sources when that pump's inlet is not fully submerged in liquid fuel. A flame arrestor installed in the fuel pump inlet line would be considered an alternate means of compliance. This action is an interim action intended to prevent mechanical pump failures from igniting vapors in the tank via the inlet line until the fuel pump design has been revalidated under item 3 above. The FAA will keep the Board informed of its progress on these actions and will provide the Board copies of any issued airworthiness directives.

From: NTSB
To: FAA
Date: 7/1/1997
Response: RECOMMENDATION A-96-175 URGENTLY CALLED FOR OPERATIONAL CHANGES THAT COULD BE INSTITUTED QUICKLY. FUEL TANK TEMPERATURES COULD BE REDUCED BY LIMITING B-747 AIR CONDITIONING USE ON THE GROUND OR BY REAPPORTIONING A SMALL AMOUNT OF THE INITIAL FUEL LOADING TO THE CWT FROM THE INBOARD MAIN FUEL TANKS. NEITHER ACTION WOULD REQUIRE AIRLINES TO PURCHASE ADDITIONAL EQUIPMENT OR FUEL. ALTHOUGH REDUCING FUEL TANK TEMPERATURES IN AIRPLANE FUEL TANKS COULD KEEP FUEL TANK TEMPERATURES BELOW THE LOWER EXPLOSIVE LIMITS OF THE FUEL. FURTHER, IF THE FAA DOES NOT BELIEVE THESE ACTIONS WOULD BE SUFFICIENT, IT COULD REQUIRE THE CARRIAGE OF SUFFICIENT FUEL IN THE CWT TO ENSURE A FUEL-AIR VAPOR THAT IS TOO RICH TO SUPPORT COMBUSTION. ALTHOUGH THIS COULD INCREASE THE COST OF AIR CARRIER OPERATIONS OF THE AFFECTED AIRPLANES, THE ACTION WOULD PREVENT CWT EXPLOSIONS. HOWEVER, THE BOARD IS DISAPPOINTED BY THE FAA'S RESPONSE TO RECOMMENDATIONS A-96-175 AND -176, WHICH PROVIDE THE OPPORTUNITY TO IMPLEMENT OPERATIONAL PROCEDURES THAT WOULD REDUCE THE POTENTIAL FOR EXPLOSIVE FUEL-AIR MIXTURES IN FUEL TANKS AND PROMPTLY CORRECT MISINFORMATION CURRENTLY PUBLISHED IN B-747 FLIGHT HANDBOOKS. THE RECOMMENDED ACTION WOULD NOT REQUIRE A POLICY CHANGE OR SIGNIFICANTLY AFFECT THE COST OF OPERATION OF THE AIRCRAFT. BECAUSE THE FAA HAS NOT INITIATED ANY IMMEDIATE ACTION IN RESPONSE TO THESE RECOMMENDATIONS, A-96-175 AND -176 ARE CLASSIFIED "OPEN--UNACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 6/27/1997
Response: The Federal Aviation Administration's (FAA) senior technical staff met with the Board's staff to address the critical technical issues raised in these safety recommendations. There is no question that the FAA shares with the Board the goal of minimizing the risk of fuel tank explosions and the belief that the reduction of ignition sources and the reduction of fuel volatility are the most promising dual paths to this objective. The FAA believes there was technical agreement in several important areas. There was agreement that more research is necessary to understand fully what happened within the center fuel tank to cause it to explode. The FAA agreed that the research needs to focus on the chemistry of fuel vapors and the energy of the ignition sources necessary to ignite those vapors. That research is already underway by the Board, through a contract with the California Institute of Technology. The FAA fully supports this effort and is willing to co-manage the program to maximize its cooperation in this very important research. A second area of agreement is the need to conduct more flight tests to understand fully the conditions in the center fuel tank and vent system that existed at the time of the accident. In early July 1997, the Board will conduct flight tests using an instrumented Boeing 747-100 airplane. These tests will provide critical data about fuel and vapor temperatures in the center wing tank, as well as other valuable information, which are necessary to understanding the difficult technical issues related to this accident. The scope and objectives of this initiative were subjects of the recent meetings of our respective staffs, and there was agreement that the outcomes of the flight tests will be critical to the understanding and resolution of these technical questions. In discussions with your staff, the FAA believes there was agreement that this flight test as well as the California Institute of Technology work are required to determine the efficacy of the safety recommendations. I believe that upon completion of these flight tests, the Board, the FAA, and the industry will have a more complete understanding of the next steps that must be taken on this critical issue. As agreed with your staff, the FAA will use these data as a foundation for the safety measures required to resolve these issues. The FAA will continue to work closely with your staff in the investigation and on the various technical activities. The FAA agrees with the Board that this scientific analysis and other tests are needed to determine the best actions to be taken with respect to the TWA 800 issues. Along with the other Board efforts that the FAA supports fully, the FAA has also asked the aviation and scientific community to provide information on research and other data related to the fuel tank issues that are raised by the Board's recommendations. Both the FAA and the Board agree that any measures taken to address these safety concerns cannot produce uncertain safety benefits, which may in fact decrease safety. The FAA also believes that the Board's staff agreed with the need to pursue other avenues of explosion prevention. The FAA has an aggressive program to pursue a further minimization of ignition sources within the fuel tanks. Such things as ground fault protection of wires in fuel tanks and more focused maintenance programs for all fuel tank components are examples of several avenues the FAA is pursuing.

From: FAA
To: NTSB
Date: 2/18/1997
Response: THE FAA STATES THAT THE AIRWORTHINESS STANDARDS OF 14 CFR PART 25 ASSUME THAT FUEL VAPOR IS FLAMMABLE, THAT CURRENT FUEL TANK DESIGN REQUIREMENTS DICTATE ELIMINATION OF IGNITION SOURCES, AND THAT THESE RECOMMENDATIONS PROPOSE MAJOR CHANGES IN THE REQUIREMENTS FUEL MANAGEMENT IN TRANSPORT CATEGORY AIRPLANES. THE FAA STATED THAT FUEL MANAGEMENT TO CONTROL THE TEMPERATURE [OF ULLAGE] IN AIRPLANE FUEL TANKS MAY HAVE LITTLE BENEFIT, AND CONTROLLING TEMPERATURE TO THE EXTENT NECESSARY TO ENSURE THAT FUEL TANK VAPOR IS NONFLAMMABLE MAY BE A TASK WITH SIGNIFICANT ECONOMIC IMPLICATIONS. INSTEAD OF RESPONDING DIRECTLY TO THE RECOMMENDATIONS OR INITIATING RESEARCH INTO HOW THE RECOMMENDATIONS MIGHT BE IMPLEMENTED, THE FAA STATED THAT IT WOULD PUBLISH, WITHIN 30 DAYS, A NOTICE ASKING FOR PUBLIC COMMENT ON THE EFFECTIVENESS AND FEASIBILITY OF THE BOARD'S RECOMMENDATIONS WAS PUBLISHED IN THE FEDERAL REGISTER ON APRIL 3, 1997.

From: NTSB
To: FAA
Date:
Response: At the 1997 Board meeting addressing the NTSB’s Most Wanted List of Transportation Safety Improvements (MWL), the Board voted to place Safety Recommendations A-96-174 through A-96-176 on the Federal MWL under the issue category “Explosive Mixtures in Fuel Tanks.” In 1997 the category's named changed to "Flammable Fuel/Air Mixture in Fuel Tanks on Transport Category Aircraft." This issue category was removed from the MWL in 2008.