Dilemmas Of Engineers Faced With Defective Design

Engineers toil hard to create products and processes for the benefits of the human race. They also improve the convenience in our everyday living and beautify our environment. They are the people who turn technological fantasies into reality.

However, while engineers may strive to reduce the hazards brought about by the application of new technologies, they are not always successful. Very often, it is not the technological barriers that they cannot overcome, but rather the obstacles placed by fellow human beings.

Major engineering projects in aeronautical and aerospace applications are normally very costly and time sensitive. Correcting a design defect can be very costly and time consuming. Economic cost consideration may not always permit major redesigning to be performed. In order to better appreciate the dilemmas faced by engineers when they are faced with design faults, we shall discuss two well-known cases. The first case is involving the Challenger Space Shuttle and the second case involves the DC-10 Jumbo Jet.

The Challenger Space Shuttle Case

For a better appreciate this case, some of the background information will be useful.

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 the 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.

On the night before the Challenger space shuttle was to be launched on Jan 28, 1986, Morton-Thiokol, the maker of the solid rockets boosters, were worried that the solid rocket boosters might cause problem due to the cold weather. They held a teleconference with NASA managers to present their concerns and recommended that the launch be postponed till the temperature rose to a more suitable level.

The NASA managers rejected the recommendation as they believed the solid rocket boosters would be able to perform well, even at the expected low temperature of 26 degree Fahrenheit as their design called for performance at as low as 31 degree Fahrenheit. Under the pressure from NASA manager, Morton-Thiokol managers changed their recommendation to proceeding with the launch, despite the strong protests from their engineers who could not prove conclusive that the filed joints were indeed faulty.

The DC-10 Jumbo Jet Case

In 1974, the first fully loaded DC-10 jumbo jet exploded over the suburbs of Paris, killing 346 people, a record at that time for a single-plane crash. This was said to be an accident waiting to happen because it was known to the designers that the design of the plane was defective because the cargo door could burst open during flight.

The fuselage of the DC-10 jumbo subcontracted to Convair by McDonnell Douglas. Dan Applegate worked as a senior engineer in Convair directing the project. Dan wrote a memo to the vice president of Convair identifying the various dangers that could arise from the design of the fuselage. He highlighted a few potential dangers, especially with regards to the possibility of disaster due to the failure of the cargo door. He detailed how the cargo doors could burst open during flight resulting in the decompression of the cargo space, leading to the collapse the floor of the passenger cabin above. When that happens, the control lines running along the cabin floor would be damaged and the plane could not be controlled.

The senior engineer therefore recommended that the doors be designed and at the same time strengthen the cabin floor. He warned that such making the changes as he recommended would lead to some of the DC-10 cargo doors being forced open during flight and plane crash would result.

While the top management at Convair did not disagree with technical analysis or warning by Applegate, they maintained that Convair might face possible financial liabilities if they were to pass on this information to McDonnell Douglas. These liabilities could be severe since the cost of redesign and the delay to make the necessary safety improvements would be very high and would occur at a time when McDonnell Douglas would be placed at a competitive disadvantage.

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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