Date: 202105
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: Hydraulic Fluid
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate; Pre-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Overcame Equipment Problem; General Maintenance Action; General Work Refused
Contributing factors: Human Factors; Company Policy; Aircraft; Procedure
Primary problem: Procedure

Narrative: After seeing my flight was delayed; I called Maintenance Control and they said they weren't able to service the hydraulic system I had written up the night before. The local maintenance didn't have the correct parts or fluid. The technician told me they were flying out the parts; fluid; and mechanics from ZZZ. I asked if hydraulic fluid was allowed to fly and they said it was fine. After the aircraft arrived and the mechanics finished servicing the aircraft; I arrived and began my preflight duties. The mechanics said they had one sealed can of hydraulic fluid and the pump tool they used to service the system. I called the on Duty Pilot and he told me it was fine as long as it was sealed and the partially used can was being left. This didn't sit right with me so I tried to find information about it in the manual. Hydraulic fluid wasn't listed but there also wasn't a phone number for the company HAZMAT specialist. I escalated the issue to the Union and they were able to find a reference in the Dangerous Goods Manual (DGM) appendix about hidden hazards. I also googled the hydraulic fluid (Mobile HyJet IV-Aplus) and found the safety data sheet listed the fluid as a Class 9 Dangerous Good. After leaving a voicemail with the Duty Pilot saying I was going to deny boarding to the fluid and equipment; the duty manager called me and asked why I was going to leave the items and that it was going to cost a lot of money to get it back to ZZZ. I referenced the DGM and they said I was good to depart.This [Hazmat violation] was either caused by ignorance of our DG policies or was negligent behavior on the part of operations. I've been told before from them that hydraulic fluid is Hazmat. They once drove 3-4 hours to another airport because of this same issue. Either way; this was a significant safety violation. A comprehensive review of DG policies and the quality of training need to happen. Either they actually didn't know or they disregarded safety policy for the sake of operational convenience. Either is scary in a 121 airline.




Synopsis: Air carrier Captain reported a Maintenance Hazmat violation regarding the transport of incorrectly configured Class 9 Hazmat.