Engineers' Dilemmas When Proceeding With Defective Design

By Author: Jacob Gan
Total Articles: 5
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It is the responsibility of engineers to create products and processes for the benefits of the human society. Engineers also enable living to be more convenient and environment to be friendlier. They are the professionals who make possible what were deemed mere scientific fantasies.

Although engineers also work to reduce the dangers that come along with technological innovations, they are not always able to eliminate the dangers that these innovations pose. The failure does not always result from technological limitations. More often than not, it is the financial consideration that cause these dangers to be insufficiently addressed.

Technological projects in the field of aerospace and aeronautics usually involve very high cost and observation of completion dates is very important. As a result, correcting a defect in the design can cost a lot in term of time and money. The recent delay in the completion of Airbus A380 super jumbo jets is a good example.

To enable us to gain an insight into what dilemmas engineers face when they encounter design faults that are very costly and time consuming to correct, ...
... we shall discuss the case involving the Challenger Space Shuttle and the case involving the DC-10 Jumbo Jet.

The Case Involving the Challenger Space Shuttle

The main vehicle in the space shuttle is the orbiter. There are three rocket engines in the orbiter, which also contains a huge cargo bay for the space lab or for satellite that will be launched from the space shuttle. Most of the liquid hydrogen fuel needed by the rocket engines is stored in a huge external tank (which also carries oxygen to support fast combustion). The external storage tank is jettisoned after about eight and a half minutes from lift-off when the fuel is used up.

The rockets in orbiter cannot provide sufficient power to send the shuttle into space because of the huge weight. The additional thrust during lift-off is provided by two external solid rocket boosters. Since the booster rockets are huge and long, they are manufactured in segments and the 5 segments are joined together at the launch site. These joints are called field joints since they are put together at the launch site. The field joints are not as sturdy as those performed in the factory and the sealing is also not as reliable. The lower performance of these field joints was apparent from the various tests. Of particular was the concern that the sealing at the joint to prevent the hot rocket air from leaking at low temperature. However, the redesigning process was slow and no new design was available.

The most significant event took place on the night of Jan 27, 1986. The Challenger space shuttle was to be launched in the morning. The maker of the solid rockets boosters, Morton-Thiokol, held a teleconference with NASA managers. The engineers at Morton-Thiokol presented their concerns about the safety of the launch. In particular, the danger due to the poor performance of the field joints under the influence of the cold weather. They recommended that the launch be postponed till the temperature rose to a more suitable level.

The NASA managers were not happy with the recommendation. There were several reasons. Apparently, they believed the solid rocket boosters would be able to perform well although the temperature was expected to be low - about 26 degrees Fahrenheit. This was because in their design specifications, the solid rocket boosters were supposed to be able to perform safely at temperature as low as 31 degrees Fahrenheit. However, it was suspected that the NASA managers were keen to launch the space shuttle without any further delay because of the following three reasons:

Reason 1: Political Pressure
President Reagan was to speak on education during his State of the Union Address while the space vehicle was to be in space. It would be an excellent time when a teacher was to circulating high above the Earth at that time.

Reason 2: Economic Pressure
NASA wanted to make the space shuttle program commercially attractive. At that time, the European Space Agency was posing too much of a competition

Reason 3: Scheduling Backlog
There had been too many delays in the past and there is a backlog of launches. In particular, the next launch was to observe Comet Halley before the Russians.

As a result of the pressure from NASA managers, Morton-Thiokol managers changed their recommendation to launch from no-launch, even though their engineers protested strongly against it.

Challenger space shuttle was launched as scheduled the next morning and it exploded, killing all the astronauts.

The Case Involving the DC-10 Aircraft

The news of the explosion of the first fully loaded DC-10 jumbo jet in 1974 over the suburbs of Paris, killing 346 people, did not surprise many engineers and managers in Convair who did the fuselage design for McDonnell Douglas.

The engineers in Convair wanted to redesign the cargo doors and to strengthen the cabin floor because they realized the defect in their design. From their calculation, they have found that the cargo door might be forced open during flight. The resulting loss of compression would lead to the failure of the passenger cabin floor where the control cables passed through. The damage to these control cables would lead to the loss of aircraft control and crash would ensue.

The top management at Convair did not inform McDonnell Douglas of the design defect because of fear of big financial cost and liabilities, as well as delay in putting the new aircraft into production.

Observations:
There are close parallels between the two cases. Both designs were known to be flawed by the engineers who tried to alert the management but the management decisions were clouded by monetary considerations which led to the eventual loss of the crafts and the lives of the occupants. In both cases, engineering hats were removed and management hats put on.

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