Date: 201502
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Aircraft component: Cargo Compartment Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting; Communication Breakdown; Time Pressure
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Attendant; Person Flight Crew
When detected: Aircraft In Service At Gate
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: During preflight; two mechanics came to the cockpit. One mechanic asked me if we had written up the vibration felt in the floor at seat 6AB. I informed him that we were just informed by the flight attendant and had not had a chance to put it into ACARS. He then told me that they did not know what was causing the vibration and 'not to write it up and we could take the aircraft.' He said that if we write it up it would delay the departure and cause them to have to open up panels. I informed him that FARs require us to write up discrepancies; I wanted it to be written up so that it would be documented and what they had done to identify and remedy the discrepancy recorded. Since we were about to go over the Pacific; into ETOPS airspace; I felt it was prudent to identify the problem.This was a clear violation of FAR and totally unprofessional with no regard for aircraft safety. This is not a unique occurrence and becoming more of the norm in maintenance operations on a daily basis; As it turned out; it was an impending equipment failure in the fire/smoke detection system.


Second narrative: Upon arrival at the aircraft we could hear a hum and feel a vibration near seats 6AB. The purser reported that she had already called for maintenance to investigate.One mechanic came to the cockpit and asked me not to write up the vibration since we would not be able to hear it once the engines and packs were turned on. I asked him what was causing the vibration and he said he did not know and that he could not determine the source of the vibration without causing a departure delay. I reminded him that [company] policy and the FAR's both require us to document any discrepancies.We entered the discrepancy in ACARS and contacted maintenance via radio. The vibration turned out to be an impending failure of a fan in the forward cargo compartment smoke detection system. The same mechanic wanted to defer the repair but reluctantly replaced the fan after we informed him that we would refuse the aircraft unless the fan was replaced.Sadly; this concept of ignoring problems to protect the on-time departure appears to be a cultural shift and jeopardizes safety.


Synopsis: A B-757 flight crew were urged by a Mechanic not to report a hum and vibration noted near seats 6AB.  They reported it anyway. The vibration turned out to be an impending failure of a fan in the forward cargo compartment smoke detection system.