Narrative:

In daylight cruise at FL400 near ZZZ1 we were deviating around a cell and entered a benign looking cloud with light radar return. The jumpseat rider noticed a flash and asked if it was lightning. First officer and I had not noticed the flash or heard anything. Shortly thereafter I noticed a smell and asked anyone else noticed something that smelled like electrical fire. Jumpseater suggested it smelled more like caps with which the first officer agreed. I picked up phone to check with flight attendants to find them already calling us to report smell in cabin. First officer continued to fly and took over ATC communications while I started the smoke/fumes/fire checklist. During checklist; flight attendants called with further reports and connected the start of the smell with light chop and a sound from the aft cargo bin that sounded like something shifting. Jumpseater was very helpful handling the calls from the cabin. We got as far as APU bleed off in the checklist; declared an emergency and advised ATC that we wanted to go to ZZZ. (We discussed ZZZ1 as a destination but given our altitude and distance required to descend elected to go for better maintenance support and customer service; with the ability to turn toward ZZZ1 in an emergency descent should the smoke not clear.) we encountered some light chop and rain which was followed by autopilot and auto-throttle disengagement; and erratic air data computer indications for a brief period. First officer managed that problem while I continued with emergency checklist. That raised some concerns about potential for a serious electrical fire but when everything returned to normal operations and the smell diminished we elected to continue a normal descent for ZZZ. I made a PA to tell the passengers that we were working on a procedure to eliminate the source of the smell and proceeding to ZZZ as a precaution. Fumes dissipated quickly as we descended toward ZZZ. We requested emergency equipment and a thermal check of the cargo bins after landing. After landing we cleared the runway and stopped for inspection. Another PA was made to tell the passengers what was going on outside. Engines were alternately secured to allow crash personnel access to the fuselage; and the cargo bins were opened for inspection. After getting the all clear; we proceeded to the gate. I apologized to the passengers for getting them to the wrong airport but pointed out at least it was the right state. Deplaning they were very complimentary of the flight attendants demeanor and our handling of the situation. ZZZ station personnel did a great job.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B757 crew suspected they had a lightning strike and shortly there after they and the Flight Attendants smelled a burning smell. An emergency was declared; the QRH procedure completed and the flight diverted to an enroute airport where an emergency landing was completed. The smoke had dissipated by landing time.

Narrative: In daylight cruise at FL400 near ZZZ1 we were deviating around a cell and entered a benign looking cloud with light radar return. The jumpseat rider noticed a flash and asked if it was lightning. First Officer and I had not noticed the flash or heard anything. Shortly thereafter I noticed a smell and asked anyone else noticed something that smelled like electrical fire. Jumpseater suggested it smelled more like caps with which the First Officer agreed. I picked up phone to check with Flight Attendants to find them already calling us to report smell in cabin. First Officer continued to fly and took over ATC communications while I started the Smoke/Fumes/Fire checklist. During checklist; Flight Attendants called with further reports and connected the start of the smell with light chop and a sound from the aft cargo bin that sounded like something shifting. Jumpseater was very helpful handling the calls from the cabin. We got as far as APU bleed off in the checklist; declared an emergency and advised ATC that we wanted to go to ZZZ. (We discussed ZZZ1 as a destination but given our altitude and distance required to descend elected to go for better maintenance support and customer service; with the ability to turn toward ZZZ1 in an emergency descent should the smoke not clear.) We encountered some light chop and rain which was followed by autopilot and auto-throttle disengagement; and erratic ADC indications for a brief period. First Officer managed that problem while I continued with emergency checklist. That raised some concerns about potential for a serious electrical fire but when everything returned to normal operations and the smell diminished we elected to continue a normal descent for ZZZ. I made a PA to tell the passengers that we were working on a procedure to eliminate the source of the smell and proceeding to ZZZ as a precaution. Fumes dissipated quickly as we descended toward ZZZ. We requested emergency equipment and a thermal check of the cargo bins after landing. After landing we cleared the runway and stopped for inspection. Another PA was made to tell the passengers what was going on outside. Engines were alternately secured to allow crash personnel access to the fuselage; and the cargo bins were opened for inspection. After getting the all clear; we proceeded to the gate. I apologized to the passengers for getting them to the wrong airport but pointed out at least it was the right state. Deplaning they were very complimentary of the Flight Attendants demeanor and our handling of the situation. ZZZ station personnel did a great job.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.