B757 flight crew reported a fume event in the flight deck during cruise and diverted safely to a nearby airport.
Synopsis
B757 flight crew reported a fume event in the flight deck during cruise and diverted safely to a nearby airport.
Narrative
While enroute from ZZZ to ZZZ1 at FL340; a strong unusual smell developed in the flight deck. The odor did not have any associated smoke; fire; or visible fumes; but it did have a sort of gaseous/chemical type aroma that was only noticeable in the flight deck. The Captain; PF; asked first if I; PM; smelled that strange odor; to which I replied that I did. We immediately donned our oxygen masks and established communication with each other while we tried to find the source of the smell. I asked the Captain if I should ask the flight attendants if they were warming something in the galley; or if they were also noticing the odor in the cabin and galley. The Captain agreed; and I called the FAs on the interphone.The Flight Attendant (FA) replied that they were heating the passenger meals. However; they did not have or noticed any smoke; smells; or similar issues in the galley. At this point I asked the FA to shut off the ovens and standby on preparing any of the first class meals for the time being. I informed the Captain of the FA response; and he called back to have the Purser come up to the flight deck; while he would go to the cabin / galley area to make his own assessment.While on the O2 mask and after positive exchange of controls; I became PF and also had the radios. As soon as the Purser stepped into the flight deck so the Captain would go to the galley area; he stated; Whoa; I definitely smell something here that is not noticeable in the cabin or galley." The Captain briefly stepped out to the cabin to make his own assessment. After a few seconds; the Captain returned; put on his mask and said he couldn't smell anything in the cabin / galley area; but still noticed that strong unusual odor when he returned to the flight deck.The Purser returned to the back; the Captain stated he would contact Dispatch and Maintenance Control; I would continue with the flight controls and radios; and that we had ZZZ2 and ZZZ3 as nearby alternatives; which he had already put on the fix page for situational awareness.The Captain began to contact the appropriate parties; but it seemed to be taking longer than usual to get a response. After a few minutes; the Captain directed me to go ahead and [request priority handling] and divert to ZZZ2; which was about 40 to 50 miles north of our position. I [requested priority handling]; communicated our issue; talked about our need to descend to 10;000 ft. now; and that we would be diverting to ZZZ2.ATC cleared us to 10;000 ft.; with a right heading towards ZZZ2. I read back the clearance and informed the Center Controller that we had 'XXX souls on board (SOB); 45 thousand lb. of fuel; or about 6 hours on board!' I did not monitor the conversation the Captain had with the company since I was mainly focused on flying the airplane.We were handed off to a different Center Controller who gave us further descent and heading instructions. I emphasized that I wanted to stay close to the airport but that we were not ready to begin the approach at that point yet. We were handed to ZZZ2 Approach who initially had us going for an RNAV approach; then asked if we preferred an ILS; to which I responded 'yes; we preferred the ILS;' so Approach replied that we would now expect the ILS to Runway XXR.After the Captain had completed the company call; briefed the FAs; and talked to the passengers; we communicated again and we finalized the steps needed to start the approach into ZZZ2. He briefed the approach even though I would be the PF for the rest of the flight. We set up our speeds; ran the descent checklist; and when we felt ready to begin the approach; we notified ATC.We were having some communication issues due to the masks we had donned. We never took them off because every time we would move the mask away from our face to loudly state something to the other; we would immediately notice that strong odor again in the flight deck.We finalized the approach; we did have to do an overweight landing; but the touchdown was smooth. We exited the runway; fire/rescue crews were standing by; and they began talking with the Captain on the Tower frequency. Captain had the rescue crew do an exterior check; focusing on the cargo doors because apparently that was one of the possible sources suggested by Maintenance on the conference call that I was unable to listen on. We were asked to shut down both engines for the inspection; they chocked our nosewheel; and the rescue crew conducted an exterior check. They stated they did not see any apparent fire or smoke issue.I personally did notice the odor dissipate slightly after engine shutdown; so I asked the Captain if we should get towed to the gate instead since we could not determine the source of that odor. The Captain agreed. However; when we talked to Operations; we were informed that the station did not have that capability or equipment for that. We had to start the left engine; and we then proceeded to taxi to the gate on our own power. We were guided and parked at the gate with no issues. I noticed the smell come back with engines and packs running again.We shut down; Captain called the Chief Pilot; and we made the appropriate maintenance write-ups for the odor and overweight landing. After shutdown; one of the fire crew members came to the flight deck and told us that he was told when the rampers opened the forward cargo door; one Ramper noticed what he described as a 'burnt Styrofoam' odor. We tried finding that Ramper afterwards but he/she was not available.Final points; we checked circuit breakers; system panels; vent areas; galleys; tablets; charging outlets; all the usual suspects to find the source of the odor. We could not find the source. At that point; our concern was that the odor could get worse; be a symptom of something worse to develop; or even cause our incapacitation; so we did the most conservative and safest thing by donning our masks and terminating the flight."
Second reporter narrative
We were flying from ZZZ to ZZZ1; somewhere between ZZZ3 and ZZZ2; at FL340 when we noticed an unusual smell in the flight deck. It was more noticeable on my side first. Then; I asked FO and eventually he started to feel it. It resembled gas/chemical smell and no sign of smoke; fire fume; or any EICAS. We called the flight attendants (FAs) and asked them to turn off the ovens to determine if the smell was coming from the cabin and I immediately called for going on oxygen masks.We couldn't explain to the flight attendants what kind of smell it was; and I couldn't get a definite answer about whether they could sense anything in the cabin. Since we were already in that environment and sense of smell usually adapts quickly; so I needed a fresh perspective. I asked my Purser to come to the flight deck to help me assess the smell and show him what we meant so it might trigger something for him and also I wanted to check the galley as well. As soon as he entered; he was shocked by the odor in the flight deck. I removed the mask and checked the front galley; I quickly returned to the flight deck; where the smell was even worse. I instructed the FA not to turn on any equipment.I put on the oxygen masks; transferred control of the plane; and looked for any relevant information in the flight manual. I noticed the fire; smoke; and fume checklist didn't apply to our situation. I contacted Dispatch and attempted a phone patch to Maintenance Control; but my satellite call kept disconnecting for some reason. I was worried about the possibility of either of us becoming incapacitated due to inhaling something unusual; especially since we were already experiencing irritation in our noses and throats. Therefore; I decided to start our descent and [requested priority handling]. I asked the FO to ensure that ATC kept us close to ZZZ2. While the FO was flying; I was finally able to reach Dispatch and Maintenance Control.Maintenance Control asked us if the ovens were on; which we had already checked. They also wanted to know if there was any visible smoke or any EICAS alerts; and we confirmed that there were none. Maintenance Control suggested that the issue might be related to something in the cargo hold; and that the recirculation fans could be bringing a smell into the flight deck. However; we decided not to turn off the fans due to concerns about the left recirculation fan nature and possibility of dropping the oxygen mask since the left fan might became a cause of that. There was no checklist for this situation; and we concluded that landing in ZZZ2 was the best course of action.Once I ended the call with Dispatch; I briefed the Purser and made a quick announcement to the passengers. When I reconnected with the FO; he was doing a great job. We were already heading toward ZZZ2 at 10;000 ft. and getting ready for the ILS approach to Runway XX Right.I briefed him on what we discussed with Maintenance Control and began working on landing performance; reminded him that we were doing overweight landing; and other tasks that were left in the box. He was already familiar with the approach and the airport; I thought a quickest way to get me familiar with the airport/approach was giving him an approach briefing myself. Once the briefing was complete; we went through descend checklist; and I took over the communications while asking the FO to land the airplane so I could better monitor the situation. We successfully landed in ZZZ2; and regarding the overweight landing; he did an excellent job. The landing was incredibly smooth.We stopped on the taxiway. I opened the flight deck window; and we removed our masks. Once we shut down the engines and opened the window; the odor began to improve. I asked the firefighters to inspect the cargo for any leaks; but they reported finding nothing. We requested Operations to tow us to the gate; but they didn't have a tow truck available. As a result; we started one engine and taxied to the gate ourselves. Once we arrived and parked at the gate; ramp personnel informed the firefighters that as soon as they opened the front cargo door; they detected a burnt Styrofoam smell." We contacted Dispatch and conducted a debrief with Chief Pilot; during which we completed several write-ups. I also spoke with Maintenance Control; and they sent me a smoke and odor questionnaire. I filled it out and returned it via email. Both my FO and I experienced irritation in our noses and throats. Following Chief Pilot's advice; we called to obtain authorization to return to work."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.