Date: 201510
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Engine Oil Seals
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Aircraft Equipment Problem Dissipated; Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Just after the landing gear was retracted after takeoff; smoke started to fill the cockpit. Donned oxygen masks and almost immediately got a red MAIN CARGO FIRE EICAS message along with an aural alert. I immediately requested a right teardrop back to land on the departure runway. The MAIN CARGO FIRE message disappeared within a minute and smoke dissipated gradually over the next couple of minutes. Landed and taxied clear; stopped and waited for Fire and Rescue to inspect the exterior and confirm nothing was burning. After Fire and Rescue cleared us; we were cleared to taxi to the gate with Fire and Rescue following us. After block in CFR came on board to inspect further. No indications remained. We and maintenance believe that the smoke was related to a blown seal from a recent engine change about 4 days prior.


Second narrative: Immediately after take off smoke appeared in the cockpit. Donned O2 masks and then received a Main Cargo Fire EICAS message and aural alert. Requested immediate turn back to land. In the turn back to the field the Main Cargo Fire Alert ceased. By the time we landed the cockpit had cleared of smoke. After clearing the runway we stopped on taxiway Delta and had CFR inspect the aircraft for any indication of actual fire. CFR reported everything looked OK. We taxied to ramp and had CFR follow us to gate. Our jumpseater; a company mechanic; reported that the courier area also filled with smoke on takeoff. CFR came on board and inspected interior of aircraft and lower cargo areas. They reported no visible indication of actual fire. Made appropriate AML entry.There may have been some confusion with ATC on what our actual problem was. They thought we reported a problem with the main cargo door and then smoke once we were on the ground. Communicating through the O2 mask and attempting to RTB expeditiously; due to Cargo Fire Alert; may have contributed to the confusion. After turning back to the field the Main Cargo Fire alert ceased and we were still high and fast for the approach. I instructed the First Officer to execute a 360 turn; with ATC's approval; to bleed off airspeed and altitude vice being unstable at 500 feet. Maintenance reported that left engine had been replaced recently and may have blown a seal.


Synopsis: B757 flight crew experienced smoke in the cockpit right after the gear is retracted; don their oxygen masks; then received a Main Cargo Fire EICAS message and aural alert. As the crew turned back to the field the cargo fire EICAS ceased and the cockpit smoke cleared before landing.