Date: 201605
Local time of day: 0601-1200
Location: LAX.Airport, CA
Flight conditions: VMC
Weather elements / visibility: Rain; Thunderstorm
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower LAX
Aircraft component: Interphone System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Line Check Airman (LCA) in left seat; OE First Officer (FO) in right seat; new LCA observing in one jumpseat and 757 FO student on pleasure travel in the other jumpseat. During the takeoff roll on 25R LAX; the FO and I began to get a gradual increase in static through our headsets. After liftoff; the static turned to a full blown loud squeal which disabled both Captain and FO communication with ATC. I instructed the FO to just continue to fly the aircraft and comply with the departure.We completed the after takeoff checklist and engaged the autopilot. By this time the observing LCA and other jumpseater realized that we were having difficulty communicating with ATC and began to help trouble shoot the problem. We leveled off at 5;000 feet and 250 KTS and complied with the routing. A slight left deviation was needed for a build up at twelve o clock. We made several attempts to establish communication by selecting different mikes; headset plugs; etc. to no avail. I set the transponder to 7600 and began reading the SID lost communication procedure aloud when the LCA observing said he was able to hear and talk to ATC on the observer audio sel panel.Once ATC communication was reestablished; we continued climbing and assessed the situation. I plugged my headset into the observer panel and used the hand mic which worked well. Once above 10;000 feet; I discussed the situation with the rest of the crew as we continued to trouble shoot the problem. All radio functions were normal using the observer panel and the decision was made to continue for the time being. Dispatch and Maintenance Control were consulted and a discussion ensued about whether or not to pull and reset any radio circuit breakers. We chose not to because all radio functions were normal with that panel. We didn't want to lose what we had. The decision was made to continue to destination. As the flight progressed; the FO noticed the squeal seemed to be isolated to the interphone system and as long as we didn't use that part of the panel the radios were useable. We proceeded and eventually diverted for weather and sent a logbook entry concerning the issue and coordinated this with Dispatch and Maintenance Control prior to departure. The LCA in the jumpseat was paramount in the successful outcome of this event. Being able to reestablish ATC communication in a timely manner on the observer panel was key.


Second narrative: After starting the takeoff roll a squeal could be heard through my headset. I could still hear ATC; but after rotation the squeal became painfully loud at the current audio panel volume and ATC was very difficult to hear. We continued our departure to the west and the Captain changed our squawk to 7600 and began the lost communication procedures for LAX. I was on my first leg as flying pilot in the aircraft receiving OE. We had a new Line Check Airman (LCA) observing and another pilot in the jump-seat. The observing LCA understood by our body language and the squawk what was happening and was able to communicate from the left rear audio panel to ATC and we accepted the handoff to LAX departure. The 2 rear audio panels were not affected by the squeal the Captain and I were hearing. We both plugged our headsets into the rear panels and were able to communicate normally. We tried to troubleshoot the audio panels; adjusting volumes; checking the O2 mask positions; inter phones etc. but nothing stopped the squeal. The noise was also present when we used the speakers. The Captain sent an ACARS message to dispatch notifying them of our communication issues. We discussed the possibility of returning to LAX; but decided to continue. Maintenance Control sent a message through ACARS about resetting VHF communication circuit breakers; but the Captain didn't want to make the situation worse than it was; we all agreed.Due to weather at destination we opted to divert. Prior to the descent the squeal had diminished or disappeared entirely. The squeal also diminished or stopped when the flight interphone volume was turned down or deselected; that was different than our previous experience. We switched our headset jacks back to the normal forward locations and landed without further issue from the audio panel. The Captain spoke with Maintenance Control about the communication issue while we re-fueled for the next flight. The flight had no communication issues. After parking at the gate maintenance plugged into the audio panel on the nose gear and the squeal returned briefly.


Synopsis: A B757 flight crew and a pilot on the jump seat described a lost communications situation that developed during the takeoff from Runway 25R at LAX. A loud squeal was heard in both pilots headsets and over the speaker making ATC inaudible. Eventually ATC is contacted using observer audio panels without the squeal. Troubleshooting indicated that the squeal may have been coming from the interphone system.