Excessive Force

A landing gear bushing was significantly over-torqued when three AMTs, a Lead Technician, and a Shift Supervisor all misinterpreted a torque setting.

■ I was assigned to work on securing an A320 right main landing gear Side Stay Bushing. I was directed by my Lead Mechanic to work with [two other AMTs]…. We briefly went over the paperwork for this phase and Lead showed us the torque was 500 foot-pounds…. I set the tooling in place, put the nut and locking tab washer in place, spun it down by hand, and then engaged the tooling to begin the final torqueing of the retaining nut. [The other AMTs] read that the final torque setting was 500 foot-pounds and that the initial torque setting was 440 foot-pounds. The torque wrench was set to 440 foot-pounds, shown to our inspector, and then attached to the tooling. Once the initial torque was reached, we (myself and our Inspector) checked the tab lock positions and it was necessary to advance the position of the retaining nut by close to 1/4 inch to align the lock tab. Once we reached 500 foot-pounds, the tab lock was still not aligned. The Inspector instructed us to back the collar off and then reapply the minimum torque of 440 foot-pounds and recheck the tab lock position. We continued this through four break/reset sequences with no better luck.

We went to the incoming midnight Supervisor and explained the dilemma. He took the paperwork and briefly perused it and then said that we should turn the issue over to the incoming crew. We turned the paperwork over to [the midnight shift Lead] and explained the problem we were having. He left with the paperwork and returned approximately 15 minutes later to show me that he read that the torque was to be no more than 500 INCH-pounds. The paperwork had “500 lbf. in” in the text. Because of this misinterpretation, the applied torque was 12 times greater than was intended in the operation.

There is a difference between the way Boeing and Airbus present this information. Boeing uses “lb-ft” for foot-pounds and “lb-in” for inch-pounds. Airbus references foot-pounds with “LBF.FT” and inch pounds with “LBF.IN”. I believe that “LBF.IN” is very confusing and led to our mistake in applying the improper torque for the job. Perhaps “LB.IN”, or spelling out “foot-pounds” or “inch-pounds” would be clearer.

An Array of Assumptions

When you assume that you have the right parts and you assume they are going on the correct engine, what could go wrong? Verification of the paperwork associated with the job could have saved a lot of time, labor and embarrassment in this wrong engine, wrong parts incident.

■ I started my service on [a B737 aircraft]…#1 engine. Another AMT was to start the fuel nozzle replacement. After I completed my service, I noticed the #2 engine cowlings were opened up so I assumed that must be the engine getting the fuel nozzles…. When the nozzles arrived, one AMT took the left side of the engine and another took the right side and they began removing the fuel nozzles to replace them. I was the third person so I was handing tools to them and getting whatever they needed….

After the Inspector had checked the engine for safety and security, I closed the #2 engine cowlings. It wasn’t until the next day that I was informed that the nozzles were the wrong part number and the work was supposed to have been done on the #1 engine. I had never looked at any of the paperwork to verify the part numbers or which engine we were supposed to work on.

Reversed Rocker Arms

It is understandable to assume that an engine would be properly assembled when received from an overhaul facility. This AMT learned, however, that it is best not to make any assumptions when it comes to aircraft maintenance.

■ The PA-28 aircraft was flying fine and compression on the two new cylinders was good. After approximately 10 hours of flight time, the pilot reported that the engine was making a knocking noise and elected to land.

The maintenance facility removed the rocker box cover on the suspect cylinder and found that the rocker arms were reversed causing a misalignment. The cylinders were received from the overhaul facility and placed on the aircraft. I should have checked to make sure the correct part number was on the correct side. I assumed that they were.

Misconnections

A Maintenance Inspector’s report reiterates the need for careful review and inspection in any maintenance procedure, but especially when manpower issues, workload, and time pressure are added to the process.

CRJ-700 Unplugged

Among other things, experienced Mechanics rely on good communication and careful attention to Job Card procedures in order to overcome adverse factors such as time pressure, stress, and fatigue. In the following incident, inexperience and poor communication exacerbated the other adverse factors confronting two AMTs. Both of them overlooked Job Card procedures that could have prevented this costly CRJ-700 oil leak.