Date: 201910
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: B747 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness
Second reporter function: First Officer; Relief Pilot
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 Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the PM (Pilot Monitoring). At 4;000 feet on approach into ZZZ; there was an acrid smell in the flight deck followed by an EICAS message 'smoke crew rest.' I immediately requested priority handling; which we got; while the relief pilot and flight Mechanic investigated further. No smoke or fire was found however the crew rest alarm was on. The 'smoke crew rest' EICAS message cleared itself after about one minute. The smell had also faded within about three minutes. I requested emergency equipment on landing as a precaution. Landing and taxi to parking was uneventful. My crew performed all task flawlessly. Kudos to them.


Second narrative: The event occurred during the Approach phase of the flight while we were being vectored to intercept the localizer RWY X. While maintaining 4;000 feet and turning right; we started to pick up a pungent sulfuric-like smell in the cockpit. Approximately a minute later; an EICAS caution message (Smoke Crew Rest) popped up. As a Relief Pilot in the third observer seat; I went to the crew bunks to further investigate the presence of smoke or possible fire and the origin of the smell. On my way back to the Crew Rest; I informed the flight mechanic as well; I proceeded to open the door to the Crew Rest Area; the smoke detector in the left bunk was going off and the smell was still as strong as in the cockpit. Furthermore; there was a medium-pitched whirring noise coming from aft the Crew Rest bunks. I could still hear this noise as I made my way back to the cockpit to inform the Captain. At this time; the EICAS message had cleared on its own but the smell continued to be just as strong. I went back to further investigate to make sure nothing had changed. The flight mechanic and I decided to open the panels and the door to the bunk supplies compartment on both bunks with flashlights to check for smoke. We did not notice any. I returned to the cockpit and informed the captain. I overheard ATC querying the Captain for souls on board and the presence of Hazmat. Landing was uneventful; the fire trucks were on standby. As we exited the runway; PACK 1 EICAS message popped up and the medium-pitched whirring noise could no longer be heard as we taxied to the ramp.


Synopsis: B747 flight crew reported an 'acrid smell' and 'Smoke Crew Rest' EICAS message annunciated during approach to landing. Relief Officer and Flight Mechanic investigated while Captain executed an uneventful landing.