Next, during our 100 / 300 hour inspection, we had
removed and cleaned the oil filter and Magnetic “chip” detectors. Removal of these items again showed no unusual accumulation of oil in the gearbox. And the oil filter housing was full of oil…Ok what next? Has to be somewhere in the turbine!! Again, as part of the 100/300hr inspection we had
removed the stainless steel scavenge oil collection (“sump”) can which is attached at the lower terminus of the #6 & 7 turbine mainline support bearing scavenge strut, located on the Power Turbine (PT) support assembly. And we had also removed the oil delivery nozzle for this section, inspected it, checked its accuracy for oil delivery to the bearing package (Target Check) and put it in carbon cleaner. We had cleaned the scavenge strut as per the Ops & Maint directions, which also included the cleaning and inspection of the sump can. I felt we were getting close to the cause, as I had seen this type of fire in the turbine one other time. The culprit then was a blocked scavenge line from this section of the oil system (the #6 and #7 mainline bearing package). Ok— let’s look. When we removed the oil scavenge hard line from the can; no oil dripped from the line; we then removed the sump can, it too was devoid of oil. And no oil came dripping out of the scavenge strut!? And how can this be? There is always some residual oil in these areas. Then a small drip of oil formed at the sump can to PT support attach point. Again — Hmmmmm! I got the mirror and flash light and looked. “What the F&%K!!?” (If nothing else we mechanics have a consistent vocabulary.) Covering the oil exit port was a piece of aluminum duct tape. And how did that get there? Well — I put it there, that’s how it got there! (More expletives.) Of course when I pulled on the tape, which came loose very easily, a bunch of oil followed and flowed onto the engine deck. And of course, since the oil was not scavenged from this section as is normal, it was forced past the air labyrinth seal for the #6 and #7 bearings and into the hot and expanding air flow from the combustion section causing our flurry of pyrotechnic / hazmat entertainment for all in the vicinity. While cleaning up the oil on the engine deck and
from the tail boom my involuntary partner in this crime and I had a discussion regarding the aluminum tape. He asked, “How did that tape get there?” “Well,” said I sheepishly. “Since we didn’t complete the job yesterday, as I wanted the oil jet to soak in the cleaner overnight, and I did not want to leave this section open, and because it was too inconvenient to find any standard aviation style plugs
I used the aluminum tape I had in my toolbox to
cover the oil exit port.” Note to all who are reading this: To say I was embarrassed is an understatement.
I had covered both the oil inlet and outlet ports for this section, to keep anything from getting into this critical bearing area while it was exposed. Good thought — improper execution! Here is what happened. We completed the job the second day of the project. As is my practice when working with another technician during the assembly procedure, we each work a side of the aircraft. When we complete the work on our side we swap sides and QC our partner’s work. I was working the left side reinstalling the oil jet, after removing the metal tape I put on the oil inlet port the day before, and oil pressure hard lines. He was on the right side installing the sump can and scavenge hard lines. I “assumed” he saw the tape on the oil exit port, I didn’t ask. My assumption was obviously wrong. He told me that he put the metal seal on the can, with a little “Permatex” on the seal, put the seal on the can, installed the can and seal in place and torqued and safetied the bolts with no difficulty. We traded sides, inspecting each other’s work and found all was as it should have been externally. Well then how did he not see the tape? Because the RR 250-C20B installation configuration on the Jet Ranger B3 is a semi-blind install for the sump can — the tape was not visible to him. Now there are lots of shoulda, coulda, woulda excuses here, but the bottom line is he wasn’t looking for metal tape as a method to cover the port — I didn’t follow-up as I assumed he knew I used tape. The results were flames, smoke and hazmat rain drops falling on our heads! We were lucky, all we got was a mess, and some
deserved humor abuse from our hangar mates. Because of the short duration of our N2 conflagration, coupled with the fact we had identified the issue, no other inspection of the turbine was required. Yes, we/I lucked out for sure. We cleaned up our mess, topped off the oil reservoir, reassembled the engine, and performed a non-eventful (a little smoke on light-off) and successful post maintenance ground run. But what happened here? This one was on me. I was the senior tech on the job. I can’t tell you how many of these inspections and strut cleanings I have done over the years.
CONFIDENCE BECAME COMPLACENCY! I used a non-standard method of covering the open oil ports. I assumed he saw me use the tape and would for sure see the tape on the support before he installed
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HelicopterMaintenanceMagazine.com December 2019 | January 2020
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