2. Observations on the Loss of the Challenger

3. Observations o Engineering processes (the decision- making process to arrive at the launch decision) need continuous review. o Learn to recognize when external pressures or conflicting interests (profits, prestige,…) cause deviations from usual engineering processes.

4. Observations o Be wary of incrementally increasing risks by normalization of deviance. o Learn to recognize, and be especially cautious in the operation of, tightly coupled and complexly interactive engineering systems. o Learn to differentiate between Primary Engineering Decisions (PED) and Primary Management Decisions (PMD)

5. Normalization of Deviance o When 1977 tests indicates some joint opening, contrary to joint designers’ expectations, a sealing putty “fix” was added, and the anomaly was considered an “acceptable risk”. o When a 1981 launch resulted in blow-by through the putty, this anomaly was explained as a result of improperly applied putty. o When 1984 and 1985 launches caused more leakage, this leakage had come to be expected, and acceptable.

6. Normalization of Deviance o If the initial seal designers were asked whether any leakage through the seal was acceptable, they probably would have not accepted any leakage. o Every instance of gas blow-by was contrary to the initial seal designers’ expectations and, yet came to be acceptable, almost expected. A “fix”, not a redesign, was always the remedy. o Deviations from initially expected behavior should always be reexamined very carefully.

7. Tightly Coupled & Complexly Interactive Systems o Processes are said to be tightly coupled when one process can rapidly affect another process. o Processes are said to be complexly interactive when they interact in unanticipated ways. o Risk is more difficult to estimate in tightly coupled and complexly interactive processes. o The solid booster seals and the shuttle fuel storage/delivery system are an example of a tightly coupled and complexly interactive system.

8. The Effects of Low Ambient Temperature o The low ambient temperature was a concern during launch review. o The critical interaction between low temperature and seal behavior was not foreseen (complexly coupled behavior). o Launch was approved in spite of the concerns about low temperature because no data existed to indicate a hazard (normalizing deviance). (No data existed to confirm the safety!--review the purpose of the pre-launch engineering process!)