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Certification Authority Incompetance

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Certification Authority Incompetance

Old 26th Sep 2000, 03:08
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Lu Zuckerman
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Thumbs down Certification Authority Incompetance

I was visiting the IASA web site and read several articles dealing with the incompetence of FAA personnel and how they didn’t let that incompetence stop them from forcing an airline out of business. I had an experience with similar incompetence when I worked on the Airbus program. As senior RMS engineer for a German company that was the lead contractor on the flap / slat drive system design I had to attend a design review meeting at the home facility of our English design partner.

The purpose of the meeting was to make a final determination about the run of the hydraulic lines that powered the wing tip brakes. Another part of the design review was to determine if it was necessary to incorporate anti flail guards on the slat drive system. The Integration contractor from Germany and the English wing designer were in favor of running the lines along the front spar as this would simplify the tubing run and it would be cheaper. To prove their design philosophy they had the English partner of the German firm conduct a test.

The test consisted of an electrical drive motor connected to a Hook’s joint that was attached to a short section of the slat drive shaft. This short shaft was supported by a live center to allow shaft rotation and the live center could also be disconnected to allow the shaft to fall as if it suffered a mechanical disconnect. They filmed the entire test and presented it to the meeting attendees. In attendance were representatives of the CAA, the LBA and the DGCA.

In the film, the shaft was brought up to design speed of about 1400 RPM. When the shaft was disconnected the shaft fell to an angle of about 20 to 30 degrees off of the drive line center. The shaft continued to rotate and it did not flail. They showed several tests filmed from different angles and each time the shaft fell and continued to rotate with out flailing. With that the certification authorities along with the wing designer and the integration contractor stated that it was not necessary to provide anti flail guards and that the hydraulic lines could be routed along the front spar. Case closed. Or, was it.

After the presentation I asked my English counterpart to step out side. I asked him if he thought there was something wrong with the test and he agreed with me that the shaft should have started to flail after dropping several degrees off drive center due to lock –up of the hooks joint.

We went back into the meeting room and every one was congratulating each other. We asked the test engineer to come outside with us. In the hall, we asked him about the test and why the Hooks joint didn’t lock up. He stated that he didn’t use a Hooks joint because the German design firm that I represented would not provide one due to a shortage and that they were behind in their delivery schedule to the integration contractor. We asked him what he had used in place of the Hooks joint and he told us that he had used a shaft and coupling from (If I remember correctly) a BAC 111 which used constant velocity joints. If my counterpart and I were not in that meeting the A310 would have the hydraulic lines routed along the front spar and there would be no anti flail guards. If in that configuration a shaft had separated the A310 would lose all three hydraulic systems which would make the aircraft a bit difficult to control.

The test was rerun using the correct Hooks joint and shaft resulting in the lines being run in front of the front spar and behind the rear spar and anti flail devices were incorporated.

The integration contractor and the wing designer in their zeal to be proven correct didn’t catch it and the certification authorities didn’t have a clue.



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The Cat
 

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