Narrative:

We were out of 9;000 ft for 8;000 ft when I noticed amber dashes on altitude alerter. We had gone into pitch mode; and we noticed that the first officer (pilot flying) had a red 'X' that appeared on his altimeter. He selected ADC1; and I ran the QRH. The aircraft had gone into heading mode inadvertently as well; and we momentarily headed left of course on our way from mersr to metropolitan. We immediately began proceeding to the right to join our course; and as we did; ATC asked if we had navigational issues. I advised them that we had a minor maintenance issue and were once again joining back on course. They accepted; and we joined our proper course to metropolitan without incident. We had already had pack 1 MEL'ed on the aircraft; and during flight; we kept getting an RA1 flashing; indicating RA2 had quit. This was sporadic and would disappear. During our descent on the phlbo arrival; we got the failure on the first officer altimeter tape. Additionally; the weather was marginal; with low ceilings around 500 ft; and visibility 4 miles. Regardless of what mechanical issues present themselves; I must remain constantly aware of the aircraft position. Broken clouds and rain. We were in and out of clouds.

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Original NASA ASRS Text

Title: EMB145 flight crew experiences an altimeter failure during descent causing the autopilot to disengage. Heading mode is selected while the QRH is consulted and NAV is not selected until after a track deviation occurs.

Narrative: We were out of 9;000 FT for 8;000 FT when I noticed amber dashes on altitude alerter. We had gone into pitch mode; and we noticed that the First Officer (Pilot Flying) had a red 'X' that appeared on his altimeter. He selected ADC1; and I ran the QRH. The aircraft had gone into heading mode inadvertently as well; and we momentarily headed left of course on our way from MERSR to METRO. We immediately began proceeding to the right to join our course; and as we did; ATC asked if we had navigational issues. I advised them that we had a minor maintenance issue and were once again joining back on course. They accepted; and we joined our proper course to METRO without incident. We had already had Pack 1 MEL'ed on the aircraft; and during flight; we kept getting an RA1 flashing; indicating RA2 had quit. This was sporadic and would disappear. During our descent on the PHLBO arrival; we got the failure on the First Officer altimeter tape. Additionally; the weather was marginal; with low ceilings around 500 FT; and visibility 4 miles. Regardless of what mechanical issues present themselves; I must remain constantly aware of the aircraft position. Broken clouds and rain. We were in and out of clouds.

Data retrieved from NASA's ASRS site as of July 2013 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.