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Safety Recommendation Details

Safety Recommendation A-96-177
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 modification of the CWT of B-747 airplanes & the fuel tanks of other airplanes that are located near heat sources to incorporate temperature probes & cockpit fuel tank temperature displays to permit determination of the fuel tank temperatures.
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: 6/7/2001
Addressee(s) and Addressee Status: FAA (Closed - Unacceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 6/7/2001
Response: The Safety Board is disappointed that the FAA does not believe in the safety benefit of this recommendation, and does not plan to take the recommended action. Accordingly, Safety Recommendation A-96-177 is classified "Closed--Unacceptable Action."

From: FAA
To: NTSB
Date: 1/19/2001
Response: Letter Mail Controlled 01/25/2001 2:19:14 PM MC# 2010064 The Federal Aviation Administration (FAA) stated in its previous letters responding to this safety recommendation that evaluations of directed ventilation and fuel tank inerting systems indicate that flightcrews would not require center wing tank temperature information. The FAA further stated that the use of ground-conditioned air discussed in response to Safety Recommendation A-96-175 does not require that flightcrews have center wing tank temperature information available. The FAA considered its action to be completed on this safety recommendation. On August 3, 2000, however, the Board classified this safety recommendation in an "open unacceptable" status pending implementation of adequate methods for reducing fuel tank flammability or for determining fuel tank temperatures. In response, the FAA evaluations of methods that could significantly reduce the exposure of transport airplane fuel tanks to flammable vapors have indicated that the two most promising methods of reducing fuel tank flammability are nitrogen inerting and cooling the fuel tanks using directed ventilation. Nitrogen inerting would reduce the oxygen content of the fuel tank ullage (vapor space) to below the level of oxygen required to support combustion of fuel vapors. Directed ventilation would cool fuel tanks located near significant heat sources (like air conditioning equipment) by ventilating areas adjacent to the fuel tanks with cooler air. The feasibility of applying these methods to in-service airplanes, new production airplanes, and new airplane designs is currently being evaluated by the FAA. The flightcrew would not require fuel tank temperature indication for either of these fuel tank flammability reduction methods. There would not be any actions the flightcrew could take to reduce fuel tank temperatures to levels that would reduce the level of or eliminate flammable vapors in the fuel tank ullage for either of these methods. Additionally, there is no flightcrew action that could be taken for existing airplane designs to reduce the fuel tank temperature to levels that would reduce or eliminate fuel tank flammability exposure. During the Board's Sunshine Meeting on August 22-23, 2000, to adopt the TWA 800 accident report, the Board's staff suggested that the flightcrew could choose not to depart from the gate for a flight if they had fuel tank temperature indication and the temperature indicated that the fuel tank was flammable. The FAA has evaluated the effect of preventing departure of a flight based on a determination that a fuel tank was flammable or a prediction that a fuel tank would be flammable at some time during the flight. Such a flight limitation would cause cancellation of a large number of flights (approximately 70 percent). Flights with no useable fuel in the center wing tank would be canceled on days when the ambient ground temperature at the airport would be above approximately 45 degrees Fahrenheit. For long-range flights with a significant quantity of fuel in the center tank, the flights would be canceled if the ambient ground temperature were above 30 degrees Fahrenheit. This limitation would be required to avoid entering the flammable regime at the top of climb. Flights would not be able to depart from most airports during the summer and all year at many airports located in warmer climates. It should also be noted that the tank temperature indication on the ground would be of no value to the flightcrew in predicting flammable conditions in the tank during the subsequent flight phases (like climb and cruise). It is clear from evaluating the environmental envelope of transport airplanes and the properties of fuels used on these airplanes that it would be impractical to implement a fuel tank temperature limit that precluded departure with flammable vapors in transport airplane fuel tanks. Therefore, the FAA has focused on nitrogen inerting as the most promising method that would provide the greatest reduction in fuel tank flammability. While the FAA shares the Board's goal of reducing flammability to the lowest practical level, it does not agree that installing fuel tank temperature indication in the fuel tanks is a practical means of achieving this goal. The FAA will continue its pursuit of implementing fuel tank inerting, which will provide the greatest improvement in safety and satisfy the intent of this safety recommendation. I consider the FAA's action to be completed on this safety recommendation.

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: FAA
To: NTSB
Date: 5/17/2000
Response: Letter Mail Controlled 05/18/2000 3:19:52 PM MC# 2000639: As stated in response to Safety Recommendation A-96-176, the FAA evaluations of directed ventilation and fuel tank inerting systems indicate that flightcrews would not require CWT temperature information. Also, the use of ground-conditioned air discussed in response to Safety Recommendation A-96-175 does not require that flightcrews have CWT temperature information available. 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: As stated in the FAA's letter dated March 3, 1998, management of fuel tank temperature on existing airplane configurations through the creation of a tank temperature "red-line" associated with tank flammability is not considered to be practical in yielding benefits in the reduction of flammability. Installation of a temperature indicator for each fuel tank is technically feasible. However, there are currently no practical, effective procedures a flightcrew could perform in flight to reduce the fuel tank temperatures significantly and the addition of another set of electrical components and wiring inside the fuel tank would add another possible source of fuel tank ignition. Airplanes loaded with fuel at typical storage temperatures, at least in the summer, would generate explosive vapors in the fuel tanks as the airplane climbs to higher altitudes. The FAA also stated that it will further evaluate the need to take the specific actions identified by the Board in this safety recommendation based on the findings of the ARAC Fuel Tank Harmonization Working Group and the team working with Dr. Shepherd on jet fuel flammability data. As stated in response to Safety Recommendation A-96-175, the work mentioned above has been completed, and the FAA has concluded that there is still no practical means of reducing fuel temperatures in fuel tanks. As stated in response to Safety Recommendation A-96-174, the FAA has begun studies of directed ventilation methods to determine if they could be effective in cooling center fuel tanks and feasible for retrofit on the existing fleet of transport airplanes. The FAA will reevaluate this recommendation after the conclusion of the studies of methods that could significantly reduce the flammability of fuel tanks. The Board has stated that certain military airplanes incorporate fuel temperature indication in all fuel tanks, including the center fuel tanks, with cockpit temperature displays for each tank. However, these fuel temperature displays are not used to determine fuel tank flammability. The additional temperature probes and displays are installed because the operation of the military aircraft involves high electrical loading for extended periods of time. The electrical equipment on those airplanes dissipates heat into the main tank fuel. Therefore, the displays are used to monitor fuel tank temperature during extended ground operation to make sure the fuel temperatures in the main fuel tanks (wing tanks) do not rise to a range that would cause degraded fuel pump performance or pump cavitation when the engines are operating at high thrust levels that require high fuel flow from the fuel pumps. This information is used to determine when to switch to ground equipment to cool the electrical equipment. With respect to fuel system feed performance on transport airplanes, the FAA believes that no benefit would be gained from additional fuel tank temperature probes. Even with the potential for the center wing tank to reach temperatures higher than the stated airplane temperature limit, the fuel system design and operation ensures sufficient fuel flow to the engines at all times. This is accomplished by requiring that the airplane's main tank boost pumps be operated at all times. In summary, the FAA has concluded that there is still no practical means of reducing fuel temperatures in fuel tanks. The FAA has initiated studies of directed ventilation methods to determine if they could be effective in cooling center fuel tanks and feasible for retrofit on the existing fleet of transport airplanes. The FAA will reevaluate this recommendation after the conclusion of the studies of methods that could significantly reduce the flammability of fuel tanks. 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: BECAUSE THE FAA HAS TAKEN NO ACTION TO IMPLEMENT A-96-177, IT IS CLASSIFIED "OPEN--UNACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 3/3/1998
Response: Letter Mail Controlled 3/5/98 4:04:27 PM MC# 980293 THE INITIATIVES UNDERWAY WITH THE ARAC AND THE TEAM WORKING WITH DR. SHEPHERD AND THE CAL TECH DATA ARE CRITICAL TO THE DEFINITION OF NEW REQUIREMENTS RELATED TO FUEL TANK DESIGNS, PROPERTIES OF FUELS AND FUEL VAPOR, AND VARIOUS MEANS TO REDUCE OR ELIMINATE EXPOSURE TO THE OPERATION OF TRANSPORT AIRPLANE FUEL TANKS WITH EXPLOSIVE FUEL-AIR MIXTURES. WITH RESPECT TO A-96-176, THE FUEL TAN TEMPERATURE LIMITS STATED IN THE FAA-APPROVED BOEING 747 AIRPLANE FLIGHT MANUAL ARE INTENDED TO PREVENT FREEZING OF THE FUEL TO ENSURE THAT THE ENGINE'S FUEL HEATING CAPABILITY WILL BE SUFFICIENT TO PREVENT FROZEN WATER IN THE FUEL FROM CLOGGING THE FUEL FILTER OR PASSAGES IN THE ENGINE CONTROL SYSTEM, AND TO ENSURE THAT THE FUEL FEED SYSTEM WILL PERFORM IN HOT WEATHER WITHOUT ANY ANOMALOUS OPERATION DUE TO EXCESSIVE FUEL VAPOR/LIQUID RATIOS WITHIN THE FUEL FEED SYSTEM. THESE LIMITS ARE NOT RELATED TO AN EFFORT TO PRECLUDE OPERATION OF THE AIRPLANE WITH A FLAMMABLE FUEL-AIR MIXTURE IN THE FUEL TANKS. FUEL TEMPERATURE INDICATION WOULD ONLY BE OF VALUE IF THE FLIGHTCREW COULD TAKE ACTION TO CHANGE THE FUEL TEMPERATURE. CURRENTLY THERE ARE NO PRACTICAL MEANS OF REDUCING FUEL TEMPERATURES. THE FAA WILL EVALUATE NEW ACTIONS ON THIS RECOMMENDATION BASED ON THE FINDINGS OF THE PREVIOUSLY REFERENCED WORK. WITH RESPECT TO A-96-177, THE FAA PREVIOUSLY STATED THAT THE MANAGEMENT OF FUEL TANK TEMPERATURE ON EXISTING AIRPLANE CONFIGURATIONS THROUGH THE CREATION OF A TANK TEMPERATURE "RED-LINE" ASSOCIATED WITH TANK FLAMMABILITY IS NOT CONSIDERED TO BE PRACTICAL. IT SHOULD ALSO BE NOTED THAT THE ADDITION OF ANOTHER SET OF ELECTRICAL COMPONENTS AND WIRING INSIDE THE FUEL TANK WOULD ADD ANOTHER POSSIBLE SOURCE OF TANK IGNITION. HOWEVER, AS ADDITIONAL TECHNICAL DATA AND INFORMATION ARE DEVELOPED THROUGH THE ONGOING ACTIVITIES, THE FAA WILL FURTHER EVALUATE THE NEED TO TAKE THE SPECIFIC ACTIONS IDENTIFIED BY THE BOARD IN THIS RECOMMENDATION.

From: FAA
To: NTSB
Date: 12/3/1997
Response: Letter Mail Controlled 3/18/98 4:46:08 PM MC# 971618: As discussed in the response to Safety Recommendation A-96-176, the purpose of the fuel tank temperature limits in Boeing's AFM's is not for the management of fuel tank temperature in order to preclude the presence of a flammable mixture in the fuel tank ullage. The FAA considers the current tank temperature indication scheme used on transport airplanes to be adequate for the purposes for which it was intended. Joint comments to the notice on this proposal from industry, operators, and manufacturers are as follows: "Flightcrew alerting procedures are based upon the concept of advising the crew when action is required and providing procedures to execute the action. The recommendation to provide the crew with center wing tank temperature information presumes that there is an action that the crew can perform to reduce the exposure of flammable fuel-air mixtures. Fuel tank flammability conditions exist to some extent on all flights, and there are no practical airplane equipment operation, airspeed, or altitude change actions that crews could take to change tank temperature sufficiently to reduce flammability exposure." Comments to the notice submitted by the Air Line Pilots Association also did not support implementation of this recommendation: "In effect, this recommendation proposes giving the flightcrew a single piece of information in a scientific and procedural vacuum. The body of knowledge required to attach significance to this temperature is just beginning to be compiled and even if that did exist, today's aircraft provide the flightcrew with very few options to affect the temperature of the fuel. Furthermore, these options are neither direct nor quick acting. "The flightcrew has no control over ambient temperature, no direct control over fuel temperature, and little control over the time of fuel loading. The only two variables within their control are altitude and operation of the air conditioning system. It must be recognized that air conditioning on a transport aircraft is not a luxury. In many environments, it is absolutely necessary for the health and safety of the passengers and is essential to provide a working environment in which the crew can perform to the best of its abilities. The net result is that the flightcrew has no guidance to enable them to effectively utilize what little control they do have." Based upon the comments received, the FAA's position is that the management of fuel tank temperature on existing airplane configurations through the creation of a tank temperature "red-line" associated with tank flammability is not considered to be practical. It should also be noted that the addition of another set of electrical components and wiring inside the fuel tank would add another possible source of tank ignition. I consider the FAA's action to be completed on this safety recommendation, and I plan no further action. The FAA looks forward to any additional technical data or information which may result from the Board's hearing next week and remains committed to identifying safety improvements which will greatly reduce, if not eliminate, the possibility of fuel tank explosions.

From: NTSB
To: FAA
Date: 7/1/1997
Response: THE SAFETY BOARD IS AWARE THAT SOME OF THESE RECOMMENDATIONS REQUEST A CHANGE IN THE CURRENT FAA POLICY THAT DOES NOT ADDRESS THE EXPLOSIVE POTENTIAL OF FUEL TANKS AND INSTEAD CONCENTRATES ON THE ELIMINATION OF IGNITION SOURCES. BECAUSE IGNITION SOURCES CANNOT BE TOTALLY ELIMINATED, HOWEVER, THE BOARD BELIEVES IT IS UNACCEPTABLE TO ALLOW EXPLOSIVE FUEL-AIR VAPORS IN FUEL TANKS OF PASSENGER-CARRYING AIRCRAFT. ALTHOUGH THE BOARD IS CONCERNED ABOUT THE LENGTH OF TIME IT TOOK FOR THE FAA TO PUBLISH THE REQUEST FOR COMMENTS, THE BOARD REGOGNIZES THE VALUE IN THE FAA SEEKING AND EVALUATING INPUT FROM THE INDUSTRY BEFORE MANDATING POLICY CHANGE THAT COULD REQUIRE SIGNIFICANT MODIFICATIONS TO PREVIOUSLY APPROVED AIR CARRIER AIRCRAFT DESIGNS. ACCORDINGLY, A-97-174 AND -177 ARE CLASSIFIED "OPEN--ACCEPTABLE 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 RESPONSE 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 SAFETY RECOMMENDATIONS PROPOSE MAJOR CHANGES IN THE REQUIREMENTS FOR FUEL TANK DESIGN AND FUEL MANAGEMENT IN TRANSPORT CATEGORY AIRPLANES. THE FAA STATED THAT FUEL MANAGEMENT TO CONTROL THE TEMPERATURE [OF THE 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.