Narrative:

During the first engine start; and just before the completion of the start sequence; the captain called for me to abort the start; which I did. He said he smelled an unusual odor; which I noticed as well. The odor was faint; and I couldn't liken it to anything familiar. Our preflight maintenance logbook inspection had revealed five write-ups for 'wet sock' or similar odors in the past three days. Following the aborted start; I opened my direct vision window to ensure the flight deck was aired out; and we coordinated a tow back to the gate. The captain checked with the flight attendants; who did not report noticing any unusual fumes or odors during the engine start. While we waited 20 minutes for the tow; we assessed ourselves for potential symptoms related to a fume event. The captain reported feeling light-headed. I noticed that I had an elevated heart rate for about 10 minutes after aborted engine start; which seemed excessive even given the anxiety our situation had caused. I didn't notice any other symptoms. The passengers disembarked at the gate and the captain wrote up the discrepancy in the maintenance logbook. We found a quiet place in the terminal to debrief and assess our fitness for flight while we waited for a replacement aircraft to be brought to the gate. An hour after the aborted engine start; the captain continued to feel light-headed and we both decided it would be best if he called in sick. I determined I was fit to fly. I continued the flight with a reserve captain on a different aircraft with no further incident.

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Original NASA ASRS Text

Title: EMB-175 First Officer reported an unusual odor during engine start.

Narrative: During the first engine start; and just before the completion of the start sequence; the Captain called for me to abort the start; which I did. He said he smelled an unusual odor; which I noticed as well. The odor was faint; and I couldn't liken it to anything familiar. Our preflight maintenance logbook inspection had revealed five write-ups for 'wet sock' or similar odors in the past three days. Following the aborted start; I opened my direct vision window to ensure the flight deck was aired out; and we coordinated a tow back to the gate. The Captain checked with the flight attendants; who did not report noticing any unusual fumes or odors during the engine start. While we waited 20 minutes for the tow; we assessed ourselves for potential symptoms related to a fume event. The Captain reported feeling light-headed. I noticed that I had an elevated heart rate for about 10 minutes after aborted engine start; which seemed excessive even given the anxiety our situation had caused. I didn't notice any other symptoms. The passengers disembarked at the gate and the Captain wrote up the discrepancy in the maintenance logbook. We found a quiet place in the terminal to debrief and assess our fitness for flight while we waited for a replacement aircraft to be brought to the gate. An hour after the aborted engine start; the Captain continued to feel light-headed and we both decided it would be best if he called in sick. I determined I was fit to fly. I continued the flight with a reserve Captain on a different aircraft with no further incident.

Data retrieved from NASA's ASRS site 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.