On the table in front of me are the quantity probe itself and the heater-fan assembly which I will be happy to show you after the hearing if you care to look at it.

In addition, on my left is a cut open tank which was subjected to a fire simulating that which actually occurred during the mission, and this tank is available for your examination.

Now, in brief, this is what happened. After assembly and acceptance testing the oxygen tank No. 2 which flew on Apollo 13 was shipped from Beech Aircraft Corp. to North American Rockwell in apparently satisfactory condition. It is now known, however, that the tank contained two protective thermostatic switches on the heater assembly. These switches were inadequate and subsequently failed during ground test operation at Kennedy Space Center.

Now, the second slide (see figure 2) shows this in a little more detail. As you can see at the top of the heater-fan assembly the word "thermostat" is shown with two arrows. These arrows point to the two thermostatic switches which failed. In addition, there is a fill tube assembly shown right here at the top of the quantity probe which was loose in a manner which I will describe in just a moment and this led to a special detanking procedure which failed those switches and ultimately damaged the wiring.

Now, in addition to these thermostatic switches which subsequently failed, it is probable that the tank contained a loosely fitting fill tube assembly which I just pointed out. This assembly was probably displaced during subsequent handling after shipment and this handling included an incident at the prime contractor's plant in which the tank was jarred.

In itself the displaced fill tube assembly was not particularly serious, but it led to the use of improvised detanking procedures at the Kennedy Space Center which almost certainly set the stage for the accident.

Now, although Beech did not encounter any problem in detanking during the acceptance test of this tank, it was not possible to detank the oxyen tank No. 2 using normal procedures at the Kennedy Space Center. Tests and analyses indicate that this was due to gas leakage through this displaced fill tube assembly that I mentioned.

Now, the special detanking procedures at Kennedy subjected the tank to an extended period of heater operation and pressure cycling. These procedures had not been used before and the tank had not been qualified by tests for the conditions experienced. However, the procedures did not violate the specifications which govern the operation of the heaters at the Kennedy Space Center.

In reviewing these procedures before the flight, officials of NASA, North American Rockwell, and Beech did not recognize the possibility of damage due to overheating. Many of these officials were not aware of the extended heater operation. In any event, the thermostatic switches might have been expected to protect the tank.

A number of factors contributed to the presence of inadequate thermostatic switches in the heater assembly. The original 1962 specifications from North American Rockwell to Beech Aircraft Corp. for the tank and heater assembly specified the use of 28 volt D.C. power which is used in the spacecraft. In 1965 North American Rockwell issued a revised specification which stated that the heater should use a 65 volt d.c. power supply for tank pressurization. This was the power supply used at Kennedy to reduce pressurization time. Beech ordered switches for the block 2 tanks but did not change the switch specifications to be compatible with 65 volt D.C.

The thermostatic switch discrepancy was not detected by NASA, North American Rockwell or Beech in their review of documentation, nor did tests identify the incompatibility of the switches with the ground support equipment at Kennedy, since neither qualification nor acceptance testing required switch cycling under load as should have been done. It was a serious oversight in which all parties shared.

Thermostatic switches could accommodate the 65 volt D.C. during tank pressurization, however, because they normally remain cool and closed. However, they could not open without damage with the 65

volt d.c. power supply. They were never required to do so until the special detanking.

During this procedure as the switches started to open when they reached their upper temperature-they were welded permanently closed or otherwise failed permanently closed by the resulting arc and were rendered inoperative as protective thermostats.

Now, the next slide (see fig. 3) shows a photograph of a switch

which was failed with this current during tests at the Manned Spacecraft Center. The drawing is in the report and in the statement that I submitted today-the photograph is in there.

Failure of the thermostatic switches to open could have been detected at Kennedy Space Center if switch operation had been checked by observing heater current readings on the oxygen tank heater control panel. Although it was not recognized at that time, the tank temperature readings indicated that the heaters had reached their temperature limit and switch openings should have been expected. As shown by subsequent tests, failure of the thermostatic switches probably permitted the temperature of the heater tube assembly to reach about a 1,000 degrees Fahrenheit in spots during the continuous eight-hour period of heater operation. Such heating has been shown by tests to damage severely the Teflon insulation on the fan motor wires in the vicinity of the heater assembly as shown in the next slide. This is

a picture of wiring which was taken from the heater assembly after the simulated tank operation in a nitrogen environment. Had this been in an oxygen environment other tests have shown that the insulation deterioration can be even worse. (See fig. 4.)

From that time on, including pad occupancy, the oxygen tank No. 2 was in a hazardous condition when filled with oxygen and electrically powered. It was not until nearly 56 hours into the mission, however, that the fan motor wiring, possibly moved by the fan stirring of the contents of the tank, shortcircuited and ignited this insulation by means of an electric arc. The resulting combustion in the oxygen tank probably overheated and failed the wiring conduit where it enters the tank. This is the tube up here [indicating] where it goes into the top of the tank, and possibly a portion of the tank itself, primarily the cap that goes through the tank at this point.

The rapid expulsion of high pressure oxygen which followed, possibly augmented by combustion of the insulation in the space surrounding the tank, blew off the outer panel to bay No. 4 in the service module, caused a leak in the high pressure system of oxygen tank No. 1, damaged the high gain antenna, caused other miscellaneous damage and aborted the mission.

The accident is judged to have been nearly catastrophic. Only outstanding performance on the part of the crew, mission control and other members of the team which supported the operation successfully returned the crew to earth.

Now, in investigating the accident to Apollo 13, Mr. Chairman, the Board has also attempted to identify those additional technical and

management lessons which can be applied to help assure the success of future space flight missions. Several recommendations of this nature are included. In addition, I would like to say that the Board recognizes that the contents of this report are largely of a critical nature. The report highlights in detail faults or deficiencies in equipment and procedures that the Board has identified. This is the nature of a review board report.

It is important, however, in our judgment, to deal with criticisms of this report in a broader context. The Apollo spacecraft system is not without shortcomings but it is the only system of its type ever built and successfully demonstrated. It has flown to the moon five times and landed twice. The tank which failed, the design of which is criticized in this report, is one of a series which has thousands of hours of successful operation in space prior to Apollo 13.

In addition, while the team of designers, engineers and technicians who have built and operate the Apollo spacecraft also has its shortcomings, the accomplishments speak for themselves. We feel by hardheaded criticism and continued dedication this team can maintain this Nation's preeminence in space.

Thank you very much.

(Mr. Cortright's prepared statement follows:)

STATEMENT OF EDGAR M. CORTRIGHT, CHAIRMAN, APOLLO 13 REVIEW BOARD, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION BEFORE THE COMMITTEE ON AERONAUTICAL AND SPACE SCIENCES, U.S. SENATE

Mr. Chairman and Members of the Committee: I appreciate this opportunity to appear before the Committee to summarize the Report of the Apollo 13 Review Board.

As you know, I presented this Report on behalf of the Board to the Administrator and Deputy Administrator on June 15, 1970. At that time, copies of the Report were given to the Members and Staff of the Committee, and the Report was made public.

This morning I would like first to outline for the Committee how the Board was established and how it organized itself to review and report on the Apollo 13 accident. Then I will cover in some detail the findings and determinations of the Board regarding the accident, including pre-accident mission events, the events of the accident itself, and the recovery procedures which were implemented to return the crew safely to earth. I will also summarize the Board's findings and determinations regarding the management, design, manufacturing, and test procedures employed in the Apollo Program as they relate specifically to the accident. Based on its findings and determinations, the Board made a series of detailed recommendations. These are set forth at the end of my statement.

ESTABLISHMENT AND HISTORY OF THE BOARD

The Apollo 13 Review Board was established, and I was appointed Chairman, on April 17, 1970. The charter of the Board was set forth in the memorandum which established it. Under this charter the Board was directed to:

"(a) Review the circumstances surrounding the accident to the spacecraft which occurred during the flight of Apollo 13 and the subsequent flight and ground actions taken to recover, in order to establish the probable cause, or causes of the accident and assess the effectiveness of the recovery actions.

"(b) Review all factors relating to the accident and recovery actions the Board determines to be significant and relevant, including studies, findings, recommendations, and other actions that have been or may be undertaken by the program offices, field centers, and contractors involved.

"(c) Direct such further specific investigations as may be necessary. "(d) Report as soon as possible its findings relating to the cause or causes of the accident and the effectiveness of the flight and ground recovery actions. "(e) Develop recommendations for corrective or other actions, based upon its findings and determinations or conclusions derived therefrom.

"(f) Document its findings, determinations, and recommendations and submit a final report."