Date: 201712
Local time of day: 0001-0600
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZZ
Aircraft component: Cabin Address System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Attendant
When detected: In-flight
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: After takeoff; cockpit crew was informed by inflight crew that 5 Flight Attendants (FAs) were still standing in the aft galley attending to safety duties; and did not hear the automated cockpit initiated command 'Flight Attendants; please be seated for takeoff.' There were no injuries. As the First Officer and flying pilot; I initiated the Before Takeoff checklist below the line; when prompted by the Captain just moments before taking the active runway. For the checklist item; 'Takeoff announcement;' I turned up the public address volume on my Audio Control Panel (ADP); and then selected the FA automated takeoff announcement at 1L on the center CDU. I listened to make sure that the announcement was transmitted; and noted that it was audibly clear; with good volume; and called that checklist item complete. The FAs who were standing in the aft galley later indicated that they didn't hear anything in that area of the cabin. FAs in the forward cabin did hear the announcement; and were  seated for takeoff. Those affected in the aft galley also commented that this seems to be a recurring issue on the fleet; and opined that the generally louder noise distractions in the aft galley; chillers running; engines; etc.; make it difficult to hear the cockpit automated announcements in the speakers directly above them in this area of the cabin. If they hear anything; it generally is faint and originates further upstream in the cabin area speakers forward of the aft galley. They indicated that cockpit commands that are initiated by the handheld mic/phone/yoke toggle switch are generally much louder and more audible if standing in the aft galley. Some inflight troubleshooting revealed a volume control bar on the FA's video screen near door 1R; that controls the cabin video audio announcements; and [it] may or may not be tied into the cockpit-automated announcements. Our inflight troubleshooting of this monitor was inconclusive. Moreover; FAs indicated that they generally don't tamper with the volume control on this screen because raising it makes their video announcements too loud; so they are trained to not tamper with this volume control bar very much. This aircraft has an MEL item; which highlights this reported problem. However; it also mentions that; if it is discovered that the automated announcements work; then we may use them. From the cockpit perspective; we could hear the announcement go out at a sufficiently high enough volume; thus; we used the automation; however; we were not aware that the volume was not sufficiently loud enough for the FAs standing in the aft galley to hear; and thus; were not seated for takeoff. We were not informed of such fact until after takeoff. This is clearly an unsafe situation; and a procedural misstep that must be modified. Henceforth; this First Officer and Captain; have decided to use the handheld devices or yoke toggle switches going forward to make a voice takeoff announcement until this MEL ceases to exist and a thorough maintenance troubleshoot has revolved this issue; once and for all.


Second narrative: MEL states 'PRERECORDED PASSENGER ANNOUNCEMENT INOPERATIVE.' It also had a NOTE: 'ANY PRERECORDED PASSENGER ANNOUNCEMENT(S) THAT OPERATE NORMALLY MAY BE USED.' Prior to departure; we tried the system and it seemed to work. However; after takeoff the flight attendants reported they never heard the announcement in the aft galley and five flight attendants were standing up in the aft galley at the start of takeoff. There were no injuries. The Flight Attendants say this is a common problem with the fleet. They suspect it may have to do with the Video Volume setting in the In-Flight Entertainment System. Ours was set at 40%. Since it was a long all night flight; we didn't want to do much trouble shooting. I think all PRERECORDED PASSENGER ANNOUNCEMENT systems on this fleet should be deactivated until this issue is resolved.


Synopsis: B777 flight crew reported using the automated announcement system prior to takeoff. Once airborne; they were notified that some of the Flight Attendants had not heard the message that was transmitted and they were not seated for takeoff.