Report of the PRESIDENTIAL COMMISSION on the Space Shuttle Challenger Accident


Chapter VII: The Silent Safety Program.



[152] The Commission was surprised to realize after many hours of' testimony that NASA's safety staff was never mentioned. No witness related the approval or disapproval of the reliability engineers, and none expressed the satisfaction or dissatisfaction of the quality assurance staff. No one thought to invite a safety representative or a reliability and quality assurance engineer to the January 27, 1986, teleconference between Marshall and Thiokol. Similarly, there was no representative of safety on the Mission Manage-ment Team that made key decisions during the countdown on January 28, 1986. The Commission is concerned about the symptoms that it sees.

The unrelenting pressure to meet the demands of an accelerating flight schedule might have been adequately handled by NASA if it had insisted upon the exactingly thorough procedures that were its hallmark during the Apollo program. An extensive and redundant safety program comprising interdependent safety, reliability and quality assurance functions existed during and after the lunar program to discover any potential safety problems. Between that period and 1986, however, the program became ineffective. This loss of effectiveness seriously degraded the checks and balances essential for maintaining flight safety.

On April 3, 1986, Arnold Aldrich, the Space Shuttle program manager, appeared before the Commission at a public hearing in Washington, D.C. He described five different communication or organization failures that affected the launch decision on January 28, 1986.1 Four of those failures relate directly to faults within the safety program. These faults include a lack of problem reporting requirements, inadequate trend analysis, misrepresentation of criticality and lack of involvement in critical discussions. 2 A properly staffed, supported, and robust safety organization might well have avoided these faults and thus eliminated the communication failures.

NASA has a safety program to ensure that the communication failures to which Mr. Aldrich referred do not occur. In the case of mission 51-L, that program fell short.


NASA's Safety Program

The NASA Safety, Reliability and Quality Assurance Program should play an important role in agency activities, for the three concerns indicated in the program title are its functions. In general terms, the program monitors the status of equipment, validation of design, problem analysis and system acceptability. Each of these has flight safety implications.

More specifically, safety includes the preparation and execution of plans for accident prevention, flight system safety and industrial safety requirements. Within the Shuttle program, safety analyses focus on potential hazards and the assessment of acceptable risks.

Reliability refers to processes for determining that particular components and systems can be relied on to work as planned. One product of such processes is a Critical Items List that identifies how serious the failure of a particular item or system would be.

Quality assurance is closely related to both safety and reliability. All NASA elements prepare [153] plans and institute procedures to insure that high standards of quality are maintained. To accomplish that goal, elements charged with responsibility for quality assurance establish procedural controls, assess inspection programs, and participate in a problem identification and reporting system .

The Chief Engineer at NASA Headquarters, has overall responsibility for safety, reliability and quality assurance. The ability of the Chief Engineer to manage NASA's safety program is limited by the structure of safety, reliability and quality assurance organizations within the agency. His limited staff of 20 persons3 includes only one who spends 25 percent of his time on Shuttle maintainability, reliability and quality assurance and another who spends 10 percent of his time on these vital aspects of flight safety.4

At Johnson, a large number of government and contractor engineers support the safety, reliability and quality assurance program, but needed expertise concerning Marshall hardware is absent. Thus the effectiveness of the oversight responsibilities at Level II was limited.5

Kennedy has a myriad of safety, reliability and quality assurance organizations. In most cases, these organizations report to supervisors who are responsible for processing. The clear implication of such a management structure is that it fails to provide the kind of independent role necessary for flight safety.

At Marshall, the director of Reliability and Quality Assurance reports to the director of Science and Engineering who oversees the development of Shuttle hardware. Again, this results in a lack of independence from the producer of hardware and is compounded by reductions in manpower, 6 the net bringing about a decrease in effectiveness which has direct implications for flight safety.


Monitoring Safety Critical Items

As part of the safety, reliability and quality assurance effort, components of the Shuttle system are assigned to criticality categories as follows:

Criticality 1

Loss of life or vehicle if the component fails.

Criticality 2

Loss of mission if the component fails.

Criticality 3

All others.

Criticality 1R

Redundant components, the failure of both could cause loss of life or vehicle.

Criticality 2R

Redundant components, the failure of both could cause loss of mission.

The assignment of criticality follows a highly detailed analysis of each Space Shuttle component to determine the effect of various ways the component could fail. This analysis always assumes the most adverse conditions with the most conservative assumptions. Any component that does not meet the fail-safe design requirement is designated a Criticality 1 item and must receive a waiver for use. A Critical Items List is produced that contains information about all Criticality 1 components. The Solid Rocket Booster Critical Items List entry for the field joint, dated December 17, 1982 is an example of this process.

Component criticality is related to test requirements in the Operational Maintenance Requirements and Specifications Document published and maintained by Level II at Johnson. For the Orbiter, the references from the Critical Items List to the requirements and specifications document are complete and traceable in both directions. The Solid Rocket Booster Critical Items List, however, does not include references to the requirements and specifications document.7 Such references would make the Critical Items List a more efficient management tool for tracking activities concerned with items critical for flight safety.

The next step in procedures documentation is the Operations and Maintenance Instruction, which develops the directives into step-by-step procedures used at Kennedy by technicians, inspectors and test personnel to accomplish each step of the hardware preparations for flight. The current Operations and Maintenance Instruction does not indicate the criticality level of components.

If the Operations and Maintenance Instruction clearly indicated when the work to be performed related to a Criticality 1 component, all concerned would be alerted that a higher than normal level of care should be used. The same point applies to production activities at Thiokol where criticality should be directly incorporated into manufacturing quality planning.


[154] Problem Reporting

Prior to 1983, Level III was required to report all problems, trends, and problem closeout actions to Level II unless the problem was associated with hardware that was not flight critical.8 Unfortunately, this requirement was substantially reduced to include only those problems which dealt with common hardware items or physical interface elements. The revision eliminated reporting on flight safety problems, flight schedule problems, and problem trends.

The change to the reporting requirements was signed by James B. Jackson, Jr., for Glynn Lunney, who was at that time manager of the National Space Transportation System (Level II manager). The change was submitted by Martin Raines, director of Safety, Reliability and Quality Assurance at Johnson.9 With this action, Level II lost all insight into safety, operational and flight schedule issues resulting from Level III problems.

On May 19, 1986, Mr. Raines wrote a memo in which he explained that the documentation change was made in an attempt to streamline the system since the old requirements were not productive for the operational phase of the Shuttle program.10 In retrospect, it is still difficult to understand why the director of Safety, Reliability and Quality Assurance at Johnson initiated this action, and it is even more difficult to understand why Level II approved it.

A review of all Level III monthly problem reports (Open Problem List) issued by Marshall during 1984 and 1985 indicates that none was distributed to Level II management. From a lengthy list of recipients, only a single copy was sent to Johnson, and that one was sent to an engineer in the flight control division. Mr. Aldrich's office and the entire Johnson safety, reliability and quality assurance directorate were not on the distribution list for the problem reports. A Rockwell International safety, reliability and quality assurance contractor at Johnson received a statistical summary of problem status, but not the actual problems descriptions.


Reporting of In-flight Anomalies

A second method of notifying Level II of problems would have been through the in-flight anomaly reporting channels. The identification and resolution of anomalies that occur during flight are addressed in Space Shuttle Program Directive 34E. For the Solid Rocket Booster, the Huntsville Operations Support Center is charged with these activities as well as other evaluations and documentation of' mission results.

"The Space Shuttle Project Managers at Kennedy, Johnson, and Marshall, and the Manager for Systems Integration are responsible for the implementation of' this directive in their respective areas."11

A letter dated October 20, 1981, from the manager of' the National Space Transportation System (Level II) addressed flight anomaly resolution:

"Beginning with the STS-2 evaluations, the enclosed new form and instructions, outlined in enclosure 1, will be utilized for all official flight anomaly closeouts. Flight anomalies will be presented for review and closeout at the Noon Special PRCB [Program Requirements Change Board]. The briefing charts will be prepared by the Project elements, and should include a schematic/graph/sketch of the problem area. This material, along with the closeout form and appropriate signatures, will become a part of the permanent closeout record. Enclosure 2 provides a sample of' closeout material from STS- 1 that would be acceptable.

"Your cooperation in this activity will be appreciated." 12

Since O-ring erosion and blow-by were considered by Marshall to be highs anomalies,13 the letter above would appear to require reporting by the Solid Rocket Booster Project Office to Level II. However, the sample closeout material attached to the 1981 letter was identified as pertaining to "Flight Test" (the first four flights). The 1983 change might well have been interpreted as superseding the 1981 Lunney letter, particularly since the program officially became"operational" in late 1982.

The reporting of anomalies (unexpected events or unexplained departures from past experience) that occur during mission performance is a key ingredient in any reliability and quality assurance program. Through accurate reporting, careful analysis and thorough testing, problems or recurrence of problems can be prevented. In an effective program, reporting, analysis, testing and [155] implementation of corrective measures must be fully documented .

The level of management that should be informed is a function of the seriousness of the problem. For Criticality 1 equipment anomalies, the communications must reach all levels of management. Highly detailed and specific procedures for reporting anomalies and problems are essential to the entire process. The procedures must be understood and followed by all.

Unfortunately, NASA does not have a concise set of problem reporting requirements. Those in effect are found in numerous individual documents, and there is little agreement about which document applies to a given level of management under a given set of circumstances for a given anomaly.


Safety Program Failures

The safety, reliability and quality assurance program at Marshall serves a dual role. It is responsible for assuring that the hardware delivered for use on the Space Shuttle meets design specifications. In addition, it acts as a "watch dog" on the system to assure that sound engineering judgment is exercised in the use of hardware and in appraising hardware problems. Limited human resources and an organization that placed reliability and quality assurance functions under the director of Science and Engineering reduced the capability of the "watch dog" role.

Much of what follows concerns engineering judgments and decisions by engineers and managers at Marshall and Morton Thiokol. It is the validity of these judgments that the Commission has examined closely. In its "watch dog" role, an effectively functioning safety, reliability and quality assurance organization could have taken action to prevent the 51-L accident.

In the discussion that follows, various aspects of the Solid Rocket Booster joint design issue discussed earlier will be reviewed in the context of safety, reliability and quality assurance. The critical issue, discussed in detail elsewhere, involves the O-rings installed to seal the booster joints.


Trend Data

Development of trend data and the possible relationships between problems is a standard and expected function of any reliability and quality assurance program. As previously noted, the history of problems with the Solid Rocket Booster O-ring took an abrupt turn in January, 1984, when an ominous trend began. Until that date, only one field joint O-ring anomaly had been found during the first nine flights of the Shuttle. Beginning with the tenth mission, however, and concluding with the twenty-fifth, the Challenger flight, more than half of the missions experienced field joint O-ring blow-by or erosion of some kind .

In retrospect, this trend is easily recognizable. According to Wiley Bunn, director of Reliability and Quality Assurance at Marshall:

"I agree with you from my purview in quality, but we had that data. It was a matter of assembling that data and looking at it in the proper fashion. Had we done that, the data just jumps off the page at you." 14

This striking change in performance should have been observed and perhaps traced to a root cause. No such trend analysis was conducted. While flight anomalies involving the O-rings received considerable attention at Morton Thiokol and at Marshall, the significance of the developing trend went unnoticed. The safety, reliability and quality assurance program, of course, exists to ensure that such trends are recognized when they occur.

A series of changes to Solid Rocket Booster processing procedures at Kennedy may be significant: on-site O-ring inspections were discontinued; O-ring leak check stabilization pressure on the field joint was increased to 200 pound per square inch from 100, sometimes blowing holes through the protective putty; the patterns for positioning the putty were changed; the putty type was changed; re-use of motor segment casings increased; and a new government contractor began management of Solid Rocket Booster assembly. One of these developments or a combination of them was probably the cause of the higher anomaly rate. The safety, reliability and quality assurance program should have tracked and discovered the reason for the increasing erosion and blow-by.

The history of problems in the nozzle joint is similar to that of the Solid Rocket Booster field joint. While several of the changes mentioned above also could have influenced the frequency.....



Pressure tests at 200 pounds per square inch of the Solid Rocket Booster joints produced bubbles in putty used to line the joints.

Pressure tests at 200 pounds per square inch of the Solid Rocket Booster joints produced bubbles in putty used to line the joints.


.....of nozzle O-ring problems, the frequency correlates with leak check pressure to a remarkable degree.

Again, development of trend data is a standard and expected function of any reliability and quality assurance program. Even the most cursory examination of failure rate should have indicated that a serious and potentially disastrous situation was developing on all Solid Rocket Booster joints. Not recognizing and reporting this trend can only be described, in NASA terms, as a "quality escape," a failure of the program to preclude an avoidable problem. If the program had functioned properly, the Challenger accident might have been avoided. The trend should have been identified and analyzed to discover the physical processes damaging the O-ring and thus jeopardizing the integrity of the joint.

A likely cause of the O-ring erosion appears to have been the increased leak check pressure that caused hazardous blow holes in the putty. Such holes at booster ignition provide a ready path for combustion gases directly to the O-ring. The blow holes were known to be created by the higher pressure used in the leak check. The phenomenon was observed and even photographed prior to a test firing in Utah on May 9, 1985. In that particular case, the grease from the O-ring was actually blown through the putty and was visible on the inside core of the Solid Rocket Booster.

The trends of flight anomalies in relation to leak check stabilization pressure are illustrated for the field joint and the nozzle joint in Figure 3, on page 133. While the data point concerning the 100 pound per square inch field joint leak check is not conclusive since it is based on only two flights, the trend is apparent.


Management Awareness

During its investigation, the Commission repeatedly heard witnesses refer to redundancy in the Solid Rocket Motor joint and argue over the criticality of the joint. While the field joint has been categorized as a Criticality 1 item since 1982 (page 157), most of the problem reporting paperwork generated by Thiokol and Marshall listed it as Criticality 1 R, perhaps leading some managers to believe-wrongly-that redundancy existed. The Problem Assessment System operated by Rockwell contractors at Marshall, which routinely updates the problem status still listed the field joint as Criticality 1R on March 7,1986, more than five weeks after the accident. Such misrepresentation of criticality must also be categorized as a failure of the safety, reliability and quality assurance program. As a result, informed decision making by key managers was impossible.



SRB Critical Items List; Dated: December 17, 1982. Failure mode & causes: Leakage at case assembly joints due to redundant O-ring seal failures or primary seal and leak check port O-ring failure- part 1


SRB Critical Items List; Dated: December 17, 1982. Failure mode & causes: Leakage at case assembly joints due to redundant O-ring seal failures or primary seal and leak check port O-ring failure - part 2

["SRB Critical Items List; Dated: December 17, 1982. Failure mode & causes: Leakage at case assembly joints due to redundant O-ring seal failures or primary seal and leak check port O-ring failure." text added for clarity, Chris Gamble, html editor]


[159] Mr. Bunn, the director of Reliability and Quality Assurance at Marshall, stated on April 7, 1986:

"But the other thing you will notice on those problem reports is that for some reason on the individual problem reports we kept sticking [Criticality] 1-R on them and that is just a sheer quality escape." 15


The Impact of Misinformation


The manner in which misinformation influences top management has been illustrated by former Associate Administrator for Space Flight Jesse Moore.

"And then we had a Flight Readiness Review, I guess, in July, getting ready for a mid-July or a late July flight, and the action had come back from the project office. I guess the Level III had reported to the Level II Flight Readiness Review, and then they reported up to me that-they reported the two erosions on the primary (O-ring) and some 10 or 12 percent erosion on the secondary (O-ring) on that flight in April, and the corrective actions, I guess, that had been put in place was to increase the test pressure, I think, from 50 psi [pounds per square inch] to 200 psi or 100 psi-I guess it was 200 psi is the number-and they felt that they had run a bunch of laboratory tests and analyses that showed that by increasing the pressure up to 200 psi, this would minimize or eliminate the erosion, and that there would be a fairly good degree of safety factor margin on the erosion as a result of increasing this pressure and ensuring that the secondary seal had been seated. And so we left that FRR [Flight Readiness Review] with that particular action closed by the project ," 16

Not only was Mr. Moore misinformed about the effectiveness and potential hazards associated with the long-used "new" procedure, he also was misinformed about the issue of joint redundancy. Apparently, no one told (or reminded) Mr. Moore that while the Solid Rocket Booster nozzle joint was Criticality 1R, the field joint was Criticality 1. No one told him about blow holes in the putty, probably resulting from the increased stabilization pressure, and no one told him that this "new" procedure had been in use since the exact time that field joint anomalies had become dangerously frequent. At the time of this briefing, the increased pressure already had been used on four Solid Rocket Motor nozzle joints, and all four had erosion. Erosion was the enemy, and increased pressure was its ally.

While Mr. Moore was not being intentionally deceived, he was obviously misled. The reporting system simply was not making trends, status and problems visible with sufficient accuracy and emphasis.


Reporting Launch Constraints

The Commission was surprised to learn that a launch constraint had been imposed on the Solid Rocket Booster. It was further surprised to learn that those outside of Marshall were not notified. Because of the seriousness of the mission 51 -B nozzle O-ring erosion incident, launch constraints were placed against the next six Shuttle flights. A launch constraint arises from a flight safety issue of sufficient seriousness to justify a decision not to launch. The initial problem description stated that, "based on the amount of charring, the erosion paths on the primary O-ring and what is understood about the erosion phenomenon, it is believed that the primary O-ring of SRM 16A [the Solid Rocket Motor on flight 51-B] never seated."17 The maximum erosion depth was 0.171 inches on the primary O-ring and 0.032 inches on the secondary. On February 12, at a Level III Flight Readiness Review, maximum expected erosion on nozzle joint O-rings had been projected as 0.070 inches for the primary and 0.004 inches for the secondary. Thus, the results far exceeded the maximum expected. If this same ratio of actual to projected erosion were to occur on a field joint, the erosion would be 0.225 inches. With secondary seal inadequacy, as indicated by Criticality 1 status, that degree of erosion could result in joint failure and loss of vehicle and crew.

The Problem Reporting and Corrective Action document (JSC 08126A, paragraph 3.2d) requires project offices to inform Level II of launch constraints. That requirement was not met. Neither Level II nor Level I was informed.


Implications of an Operational Program

Following successful completion of the orbital flight test phase of the Shuttle program, the system was declared to be operational. [160] Subsequently, several safety, reliability and quality assurance organizations found themselves with reduced and/or reorganized functional capability. Included, notably, were the Marshall offices where there was net attrition 18 and NASA Headquarters where there were several reorganizations and transfers.

The apparent reason for such actions was a perception that less safety, reliability and quality assurance activity would be required during "routine" Shuttle operations. This reasoning was faulty. The machinery is highly complex, and the requirements are exacting. The Space Shuttle remains a totally new system with little or no history. As the system matures and the experience changes, careful tracking will be required to prevent premature failures. As the flight rate increased, more hardware operations were involved, and more total in-flight anomalies occurred. 19 Tracking requirements became more rather than less critical because of implications for the next flight in an accelerating program.

Two problems on mission 61 -C were not evaluated as part of the review process for the next flight, 51 -L. A serious failure of the Orbiter wheel brake was not known to the crew as mission 51 -L lifted off with a plan to make the first Kennedy landing since a similar problem halted such operations in April, 1985. 20 Secondly, an O-ring erosion problem had occurred on mission 61-C, and while it had been discovered, it had not been incorporated into the Problem Assessment System when mission 51 -L was launched. 21 If the program cannot come to grips with such critical safety aspects before subsequent flights are scheduled to occur, it obviously is moving too fast, or its safety, reliability and quality assurance programs must be strengthened to provide more rapid response.

The inherent risk of the Space Shuttle program is defined by the combination of a highly dynamic environment, enormous energies, mechanical complexities, time consuming preparations and extremely time-critical decision making. Complacency and failures in supervision and reporting seriously aggravate these risks.

Rather than weaken safety, reliability and quality assurance programs through attrition and reorganization, NASA must elevate and strengthen these vital functions. In addition, NASA's traditional safety, reliability and quality assurance efforts need to be augmented by an alert and vigorous organization that oversees the flight safety program.


Aerospace Safety Advisory Panel

The Aerospace Safety Advisory Panel (the "panel" in what follows) was established in the aftermath of the Apollo spacecraft fire January 27, 1967. Shortly thereafter the United States Congress enacted legislation (Section 6 of the NASA Authorization Act, 1968; 42 U.S.C. 2477) to establish the panel as a senior advisory committee to NASA. The statutory duties of the panel are:

"The panel shall review safety studies and operations plans referred to it and shall make reports thereon, shall advise the Administrator with respect to the hazards of proposed operations and with respect to the adequacy of proposed or existing safety standards, and shall perform such other duties as the Administrator may request."

The panel membership is set by statute at no more than nine members, of whom up to four may come from NASA. The NASA Chief Engineer is an ex-officio member. The staff consists of full-time NASA employees, and the staff director serves as both executive secretary and technical assistant to the panel.

The role of the panel has been defined and redefined by the members themselves, NASA senior management and members of the House and Senate of the U.S. Congress. The panel began to review the Space Shuttle program in 1971, and in its 1974 annual report, it documented a shift in focus:

"The panel feels that [a] broader examination of the programs and their management gives them more confidence than in limiting their inquiry to safety alone." 22

Over ensuing years, the panel continued to examine the Space Shuttle program including safety, reliability and quality assurance; systems redundancy; flight controls; and ground processing and handling, though management issues continued to dominate their concerns. Following the first flight of the Shuttle, the panel investigated a wide variety of specific subjects, to include the lightweight External Tank, the [161] Centaur and Inertial Upper Stage programs, Shuttle logistics and spare parts, landing gear, tires, brakes, Solid Rocket Motor nozzles and the Solid Rocket Motor using the filament-wound case. There is no indication, however, that the details of Solid Rocket Booster joint design or in-flight problems were ever the subject of a panel activity. The efforts of this panel were not sufficiently specific and immediate to prevent the 51 -L accident.


Space Shuttle Program Crew Safety Panel

The Space Shuttle Crew Safety Panel, established by Space Shuttle Program Directive 4A dated April 17, 1974, served an important function in NASA flight safety activities, until it went out of existence in 1981. If it were still in existence, it might have identified the kinds of problems now associated with the 51-L mission. The purpose of the panel was twofold: (1) to identify possible hazards to Shuttle crews and (2) to provide guidance and advice to Shuttle program management concerning the resolution of such conditions.

The membership of the panel comprised 10 representatives from Johnson and a single representative each from Dryden (the NASA facility at Edwards Air Force Base, California), Kennedy, Marshall and the Air Force.

The panel was to support the Level II Program Requirements Control Board chaired by the project manager, and recommendations were subject to Control Board approval.

From 1974 through 1978, the panel met on a regular basis (24 times) and considered vital issues ranging from mission abort contingencies to equipment acceptability. The membership of the panel from engineering, project management and astronaut offices ensured a minimum level of safety communications among those organizations. This ceased to exist when the panel effectively ceased to exist in 1980. 23 NASA had expected the panel to be functional only "during the design, development and flight test phases" and to "concern itself with all vehicle systems and operating modes." 24 When the original chairman, Scott H. Simpkinson, retired in 1981, the panel was merged with a safety subpanel that assumed neither the membership nor the functions of the safety panel. After that time, the NASA Shuttle program had no focal point for flight safety.


The Need for a New Safety Organization

The Aerospace Safety Advisory Panel unquestionably has provided NASA a valuable service, which has contributed to the safety of NASA's operations. Because of its breadth of activities, however, it cannot be expected to uncover all of the potential problems nor can it be charged with failure when accidents occur that in hindsight were clearly probable. The ability of any panel to function effectively depends on a focused scope of responsibilities. An acceptable level of operational safety coverage requires the total combination of NASA and contractor organizations, working more effectively on a coordinated basis at all levels. The Commission believes, therefore, that a top-to-bottom emphasis on safety can best be achieved by a combination of a strong central authority and a working level panel devoted to the operational aspects of Shuttle flight safety.



1. Reductions in the safety, reliability and quality assurance work force at Marshall and NASA Headquarters have seriously limited capability in those vital functions.

2. Organizational structures at Kennedy and Marshall have placed safety, reliability and quality assurance offices under the supervision of the very organizations and activities whose efforts they are to check.

3. Problem reporting requirements are not concise and fail to get critical information to the proper levels of management.

4. Little or no trend analysis was performed on O-ring erosion and blow-by problems.

5. As the flight rate increased, the Marshall safety, reliability and quality assurance work force was decreasing, which adversely affected mission safety.

6. Five weeks after the 51-L accident, the criticality of the Solid Rocket Motor field joint was still not properly documented in the problem reporting system at Marshall.


[162] References

1. Commission Interview Transcript, April 3, 1986, page 2538.
2. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., pages 42-43
3. Commission Interview Transcript, Silveira, M., April 16, 1986, Washington, D.C., page 4.
4. Commission Interview Transcript, Quong, H., April 11. 1986, Washington, D.C, , pages 29-30.
5. Commission Work Session, March 25, 1986, JSC, page 84.
6. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., page 89.
7. SRB Critical Items List, Change 2, November 30, 1983, page A6 -A
8. Space Shuttle Program Requirements Control Board Directive-Level II, PRCBD Number 501152A, JSC, April 4, 1975, pages 2-4
9. Space Shuttle Program Requirements Control Board Directive-Level II, PRCBD Number 521701R2, JSC, March 7, 1983, pages 1 -6.
10. Letter from Martin L. Raines, JSC, ND5/86-M 121, May 19, 1986.
11. Space Shuttle Program Manager Directive 34E, September 3, 1982, page 2.
12. Letter from Glynn Lunney, JSC, WA-81-LO38, October 20, 1981.
13. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., page 4
14. Commission Interview Transcript, Bunn, W, April 17, 1986, Washington, D.C., page 41.
15. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., page 13.
16. Commission Interview Transcript, Moore, J., April 8, 1986, NASA Headquarters, page 19.
17. Marshall Space Flight Center Record Number AO9288, February 26, 1986, page 2.
18. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., pages 85-86.
19. Commission Interview Transcript, Bunn, W., April 17, 1986, Washington, D.C., pages 78-79.
20. Commission Hearing Transcript, April 3, 1986, page 2552.
21. Marshall Space Flight Center Record Number A07934, March 7, 1986, page 6.
22. Annual Report, Aerospace Safety Advisory Panel, 1974, page 4.
23. Report, "Space Shuttle Crew- Safety Panel History," JSC, April 16, 1986, pages 4-6.
24. Space Shuttle Program Directive 4A. JSC. April 17, 1974, page 1.

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