Challenger 350
Troubleshooting
Aircraft Equipment Problem Less Severe
General Maintenance Action
Aircraft; Human Factors
On preflight I noticed what I thought was oil coming from vents underneath the left engine cowl. The oil was streaming all the way down the underside of the engine cowl to the very end where the thrust reversers meet the cowl. It was very clear to see with absolutely no ambiguity. I took a number of pictures of this and inspected it very closely and made a decision that it would need to be documented and evaluated properly before we could justify powering up that engine. I reported this to the co-captain who saw the oily substance and agreed with my assessment. I called this in to [Maintenance Control] and spoke with [the Maintenance Controller]. He was pleasant and asked that I document the squawk and told me which chapter to use from the maintenance manual. About 20 minutes after speaking with him I was sitting in the cabin of the airplane working on documenting the squawk and Mechanic A walked in and identified himself as with [Company] maintenance. He asked me to come and show him where the oil leak was. I told him it is underneath the left engine cowl. He reported to me that he had inspected the area and could see nothing. I looked at him over the top of my glasses and asked him to give me a few minutes as I was documenting the discrepancy and I would be out there shortly. I walked outside and went under the left engine with Mechanic A who proceeded to tell me that the substance I was seeing was really nothing. He stated that it was nothing more than the carbon deposits that are normal from the brushes on the generator. The problem with this explanation is that the generators on this aircraft are in fact brushless. When I heard this explanation I began recording a video of the transaction. He was pointing at the area and rubbing on the oily substance explaining to me that it's nothing more than carbon deposits and is normal. I explained to him that I completely disagree and that I have already documented it anyway and they can deal with it however they want to. After this transaction took place I went back into the cabin of the airplane. A few minutes later the maintenance tech that was assigned to work the airplane came inside and checked in with us. He was very pleasant and asked if I had already written it up. I responded that I had already done so. He said; 'ok no problem I will have a look.' About 20 minutes later the tech came back inside the cabin and reported to us that it was a hydraulic leak. He showed me outside with the cowl off the airplane a loose fitting located just under the vents where I originally saw the fluid trailing from. There was clearly a leak of hydraulic fluid coming from this loose fitting. The tech wrenched it down by hand and that is all that was required to fix the airplane. Here is the problem; Mechanic A was wrong. He was wrong about the carbon deposits coming from the generator brushes since the aircraft has brushless generators. He was wrong about not seeing an oily substance underneath the left engine cowl since there was in fact a leaky hydraulic fitting that was clearly spilling out underneath the cowl. Finally and most importantly he was wrong about interfering with a crew member during a safety sensitive operation. I certainly don't mind speaking with and working with a maintenance rep on a maintenance item; but I would encourage the maintenance team to send someone out to speak with me who is capable of making an objective assessment. Someone who can at least acknowledge what is clear to see and does not literally make up systems on the airplane that do not exist to fit his narrative of what is wrong with the airplane. I consider this event as interfering with a crew member's ability to conduct safety sensitive operations. Had I not been confident in my knowledge; understanding and experience with the airplane I might have conceded to Mechanic A's incorrect evaluation. Had I been a new captain in the airplane I might have taken him at his word and (given his position) assumed he knew what he was talking about. Fortunately I had already documented the discrepancy; but had I not done so and given the former possible scenarios then it's possible I could have made a different decision based on Mechanic A's incorrect assessment; evaluation and inadequate knowledge of the aircraft's systems. My recommendation is to make sure that we all keep an open mind as it relates to safety sensitive operations. Let's not send reps out to the airplane to discuss the maintenance issue if those reps are not willing to remain objective; conservative and keep an open mind. I don't know what kind of pre conceived notions Mechanic A brings to the airplane when he is looking at an oily substance streaming down the underside of the cowl. As far as I am concerned and as it relates to high pressure hydraulic lines in close proximity to the high heat generated by the combustion of jet fuel in the engine core my take on the subject must be different. I don't just take a cursory examination of the situation and instantly wave it off as nothing. I have a tendency to think of things that could happen such as fires; smoke; loss of pressurization due to having to shut off bleed air; inflight emergencies due to loss of hydraulics or any combination of the above.
CL35 Captain reported having a dispute with a Maintenance manager concerning a leak coming from the engine discovered during pre-flight inspection.