Narrative:

Shortly after reaching FL330 TCAS issued an RA for traffic on our nose at FL333. We did not see another aircraft. The first officer followed the descending RA. At approximately 300 ft below cruise altitude the RA disappeared. The TCAS did not issue a 'clear of conflict' message. We returned to FL330 and advised ATC. Center replied that there were no other aircraft near us. Within two minutes the TCAS repeated the same RA; traffic on the nose; 300 ft above us. We continued to look for the traffic and placed the transponder in xpdr. While leaning forward; head over the glare shield; to look through the upper part of the window; I started to pick up the smell of something electrical burning. The first officer confirmed the smell. The odor was very faint at this point. We attempted to find its source. The smell seemed to be coming from the forward part of the cockpit. The smell gradually got stronger. We put on the oxygen masks; and accomplished the smoke/fire/fumes qrc and checklist. We declared an emergency with center and diverted to the nearest suitable airport. I told the purser that we had a burning electrical odor and that we would be on the ground in 20 minutes. The flight attendants; at that point; were in the midst of the breakfast service. Within 10 minutes the purser called back to say that the cabin was ready and that the flight attendants in the back of the cabin were starting to smell the odor. As we continued the flight attendants reported that the smell had worked its way up through the entire cabin. The flight attendants also said that the smell seemed to come in waves and was increasing in intensity. The odor was getting worse. At that point we were passing through 10;000 ft. We then decided to accomplish the smoke or fumes removal checklist. After the aircraft was depressurized the flight attendants said that the cabin air improved dramatically. The landing was normal and the equipment was standing by. We did not feel that an evacuation was necessary. The smell was not increasing and neither the flight attendants nor the fire fighters observed any sign of smoke or fire. We continued to the gate to deplane the passengers. In my opinion; the crew could not have performed any better. However; the microphones on our oxygen masks were very poor. It was extremely difficult for the purser to understand me. The first officer and I also had to repeat most of what we said to each other.

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Original NASA ASRS Text

Title: Following maneuvering; in response to a phantom TCAS RA; the flight crew of a B757-200 diverted to a nearby airport due to the smell of smoke in the cockpit. No source for the odor was determined.

Narrative: Shortly after reaching FL330 TCAS issued an RA for traffic on our nose at FL333. We did not see another aircraft. The First Officer followed the descending RA. At approximately 300 FT below cruise altitude the RA disappeared. The TCAS did not issue a 'clear of conflict' message. We returned to FL330 and advised ATC. Center replied that there were no other aircraft near us. Within two minutes the TCAS repeated the same RA; traffic on the nose; 300 FT above us. We continued to look for the traffic and placed the transponder in XPDR. While leaning forward; head over the glare shield; to look through the upper part of the window; I started to pick up the smell of something electrical burning. The First Officer confirmed the smell. The odor was very faint at this point. We attempted to find its source. The smell seemed to be coming from the forward part of the cockpit. The smell gradually got stronger. We put on the oxygen masks; and accomplished the smoke/fire/fumes QRC and checklist. We declared an emergency with Center and diverted to the nearest suitable airport. I told the Purser that we had a burning electrical odor and that we would be on the ground in 20 minutes. The flight attendants; at that point; were in the midst of the breakfast service. Within 10 minutes the Purser called back to say that the cabin was ready and that the flight attendants in the back of the cabin were starting to smell the odor. As we continued the flight attendants reported that the smell had worked its way up through the entire cabin. The flight attendants also said that the smell seemed to come in waves and was increasing in intensity. The odor was getting worse. At that point we were passing through 10;000 FT. We then decided to accomplish the smoke or fumes removal checklist. After the aircraft was depressurized the Flight Attendants said that the cabin air improved dramatically. The landing was normal and the equipment was standing by. We did not feel that an evacuation was necessary. The smell was not increasing and neither the Flight Attendants nor the fire fighters observed any sign of smoke or fire. We continued to the gate to deplane the passengers. In my opinion; the crew could not have performed any better. However; the microphones on our oxygen masks were very poor. It was extremely difficult for the Purser to understand me. The First Officer and I also had to repeat most of what we said to each other.

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.