UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Posted (7 years 4 months 1 week 3 days 22 hours ago) and read 3454 times:
Here's a scenario for all you CRJ mechs. See if you can figure out what's wrong.
Aircraft in question takes a dump upon start attempt of #2 engine. Crew write-up was as follows: During #2 engine start, received no N2 rotation, no oil pressure, no lightoff.
MX changed the start valve and it checked good, but did not fix original write-ups. Cannon plugs were cleaned for the oil pressure transducer as well as all the harness connectors(blue, red, and yellow). No fix. #2 engine oil sump chip detector light was illuminated. Some debris noted on chip detector. Debris was cleaned and light reset.
I took the turnover from there. Upon examining the #2 engine, I found the ATS leaking oil, and the oil inside the ATS looking like molasses. It was blueish in color and looked like it was severely contaminated. I changed the ATS after conferring with MC. Ops check good (dry motoring), but original problems still present. N2 reading on EICAS stays at zero, and no oil pressure while motoring. N1 was normal, ITT was normal (ambient temp), and rotation was physically observed out at the engine. After two dry motorings, the chip detector was lit again. Some small flakes were found this time. I had a hunch something was eating itself in the AGB at this point.
As for the no lightoff problem, I did some digging in the MDC. I found the #2 engine fuel SOV failed several times in the last few weeks. Sure enough, I found the SOV was failed closed, even though EICAS showed it functioning normally. This explains the no lightoff which occured with the crew, as the engine wasn't getting any fuel. They are in the process of changing out the SOV actuator as we speak (not fun). However, the lack of oil pressure and N2 still remain at the present time. G.E. is not sure what's going on. We are baffled as the three writeups appear to have little in common with each other, except that they all involve #2 engine. We were leaning toward changing the N2 alternator and the oil pressure transducer, but we ran out of time. The aircraft is still AOG. Has anyone ever seen these symptoms on a CF34-3B1? Beside the DCUs, what is common to oil pressure and N2? The aircraft has been dead for 3 days now at an outstation. Thanks!
Ilikeyyc From United States of America, joined Dec 2003, 1373 posts, RR: 22 Reply 1, posted (7 years 4 months 1 week 3 days 19 hours ago) and read 3435 times:
As a new crj mech (and I do C checks, not line mx), I don't know very much, but let me take a stab in the dark:
Something has broken on the N2 shaft that physically prevents N2 from turning. It is causing wear on the N1 shaft therefore producing metal. A larger chunk of metal has worked its way through the oil return line and is either clogging the line, or physically preventing the oil pump from turning.
again, shot in the dark. let me know what you find out!
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 4, posted (7 years 4 months 1 week 3 days 17 hours ago) and read 3395 times:
Quoting Ilikeyyc (Reply 1): Something has broken on the N2 shaft that physically prevents N2 from turning. It is causing wear on the N1 shaft therefore producing metal. A larger chunk of metal has worked its way through the oil return line and is either clogging the line, or physically preventing the oil pump from turning.
If N2 is actually not turning, N1 will not turn either (it will only turn due to airflow induced by N2 rotation). Sounds more like an accessory drive failure which should be driving the oil pump and the N2 rpm transducer. If it also drives the fuel control unit pump that might explain the lack of a light off.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Ilikeyyc From United States of America, joined Dec 2003, 1373 posts, RR: 22 Reply 5, posted (7 years 4 months 1 week 3 days 17 hours ago) and read 3387 times:
Quoting Jetlagged (Reply 4): If N2 is actually not turning, N1 will not turn either (it will only turn due to airflow induced by N2 rotation). Sounds more like an accessory drive failure which should be driving the oil pump and the N2 rpm transducer. If it also drives the fuel control unit pump that might explain the lack of a light off.
I hate to show that I know so little, but I am new to the airplane, and 90% of my work is on the airframe. But I am learning something new all of the time. Anyway, 'Bagsmasher said that the fuel SOV failed in the off position, so that is what caused the failed light off.
So that leaves me with the questions of where is the N2 rpm transducer? If the MCD contains metal after a cleaning and 2 dry motors, does that mean that the oil is flowing? If so then the oil pump is working?
UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Reply 7, posted (7 years 4 months 1 week 3 days 7 hours ago) and read 3334 times:
The N2 alternator on the #2 engine is mounted on the lower inboard side of the accessory gearbox. You can gain access by removing one of the green accoustical liner panels in the bypass duct. It is attached to the blue harness back there. I am going to make a call and see if they have found anything yet. I'm curious now.
Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Reply 8, posted (7 years 4 months 1 week 2 days 21 hours ago) and read 3259 times:
Quoting Jetlagged (Reply 4): If N2 is actually not turning, N1 will not turn either (it will only turn due to airflow induced by N2 rotation). Sounds more like an accessory drive failure which should be driving the oil pump and the N2 rpm transducer. If it also drives the fuel control unit pump that might explain the lack of a light off.
Sorry for my limited knowledge, but I'm trying to get a better picture of how a jet egnine is working/constructed.
Lets see if I get this right. N1 is the speed of the LP compressor while
N2 is HP speed. Both are located on different drive shafts. N1 is driven by LP turbine (rearmost turbine spool) while N2 is driven by HP rurbine (first turbine spool).
So what you are saying is that if the HP turbine isn't turning, the LP turbine will be stuck too.
Wouldn't there still be some kind of airflow through the HP section creating atleast some LP movment and thus N1 readings.
Also isn't the AGB connected through some kind of drive shaft that will break if the AGB messes up in order to prevent damage to the engine turbine shafts.
Hope I didn't confuse you or myself to much in this post
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 9, posted (7 years 4 months 1 week 2 days 16 hours ago) and read 3233 times:
Quoting Tg 747-300 (Reply 8): So what you are saying is that if the HP turbine isn't turning, the LP turbine will be stuck too.
Wouldn't there still be some kind of airflow through the HP section creating atleast some LP movment and thus N1 readings.
Yes, if for some reason the HP spool is seized, the starter motor cannot turn it, so there is no airflow induced through the engine, so the LP spool will not turn either.
The LP spool isn't stuck. It can turn independently due to windmilling for example. However the air turbine starter only acts on the HP spool. It has no direct effect on the LP spool.
Perhaps you were imagining starter air being blown onto the HP and LP turbines directly?
The fact that the LP spool was seen to turn normally shows that there was normal N2 rpm during the dry crank, even though there was no N2 indication on EICAS.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Reply 10, posted (7 years 4 months 1 week 2 days 15 hours ago) and read 3226 times:
Thanks, I think i forgot that we are talking about the start sequence here. I for some reason was assuming the airflow from combustion etc. to be present, and thus found it a bit strange what you were saying about stuck turbines etc.
Also Its very easy to forget that bleed air is acting on the start engine, and not on the "main engine" it self.
UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Reply 11, posted (7 years 4 months 1 week 23 hours ago) and read 3152 times:
Well, the verdict is in. The next crew of mech's who were sent to the outstation were instructed to drain the engine oil. After draining it into a clean container, a layer of powdery metal was seen coating the oil's surface. A new engine is currently enroute and should be changed sometime tomarrow. Apparently the AGB ate itself resulting in the loss of N2 indication and oil pressure. Thanks for the responses!
UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Reply 14, posted (7 years 4 months 5 days 9 hours ago) and read 3064 times:
Ballpeeen, yes, I hear they got the hangar back a couple days later. FYI, the same aircraft is now dead again in PHL with a nosegear door master caution problem. When it rains it pours I guess.
UAL Bagsmasher From United States of America, joined Sep 1999, 2131 posts, RR: 11 Reply 16, posted (7 years 4 months 1 day ago) and read 2951 times:
Ballpeeen LOL Yeah...something about the static inverter roasting itself and the associated wiring. Haha, those guys just got back to town yesterday after 2 or 3 days on their road trip. At least someone is making OT.
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