Narrative:

Air carrier X departed pit on schedule. En route climb I noticed my main altimeter was bouncing 1000 ft either way and 'off' flag coming into view intermittently. As I was flying this leg, I put aircraft on autoplt at level off. Altimeter continued to oscillate, but standby altimeter is on left side and it worked properly. No autoplt problems yet. As we neared martinsburg VOR and first officer received the ATIS. I told first officer that he would make the approach as I was not going to try and approach with my altimeter oscillating - selection of our alternate static source or air data computer did not correct altimeter problem. At this time we were in descent and first officer shifted our guidance computer to #2 so first officer would be flying on correct autoplt. I also felt and first officer admitted shifting flying duties in midstream is sometimes complicating as we adjusted for a low approach. Due to bwi approach in its usual backup position, we were #8 for the ILS 10. Our preliminary cockpit duties and approach briefing were completed as we descended on vectors and reduced speed for the approach. After turning on the ILS inbound, approach requested we maintain 170 KTS, and slowed. Our autoplt kicked off 3 times during our initial GS intercept, with immediate placement back to on and recapture, we noticed on TCASII that traffic separation was now down to 3 mi as we called tower for landing clearance out of 2000 ft outside the LOM. Tower said to maintain 170 KTS and not 20 seconds later our of 1600 ft we were given turn to 180 degrees and climb to 2000 ft. First officer punched toga buttons and immediate power application shot aircraft skyward to climb and passed 2000 ft in turn. I told first officer to 'maintain 2000 ft' and he finally kicked off autoplt to recapture altitude as we shot by it to 2350 ft. My altimeter was useless. The standby as accurate. But I'm trying to keep an eye on first officer side as things seem to get crappy. Approach said nothing as we releveled at 2000 ft and turned us out to follow new traffic for another ILS. Traffic ahead of us on 1ST approach slowed up and spacing by ATC was absolutely terrible. First officer mentioned ATC does this a lot and causes their own problems. As we re-intercepted ILS 10 we slowed to 150 KTS and told approach we're not going around again.

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Original NASA ASRS Text

Title: ACR X CLB THROUGH ASSIGNED ALT. PLTDEV. NON ADHERENCE TO ATC CLRNC.

Narrative: ACR X DEPARTED PIT ON SCHEDULE. ENRTE CLB I NOTICED MY MAIN ALTIMETER WAS BOUNCING 1000 FT EITHER WAY AND 'OFF' FLAG COMING INTO VIEW INTERMITTENTLY. AS I WAS FLYING THIS LEG, I PUT ACFT ON AUTOPLT AT LEVEL OFF. ALTIMETER CONTINUED TO OSCILLATE, BUT STANDBY ALTIMETER IS ON L SIDE AND IT WORKED PROPERLY. NO AUTOPLT PROBLEMS YET. AS WE NEARED MARTINSBURG VOR AND FO RECEIVED THE ATIS. I TOLD FO THAT HE WOULD MAKE THE APCH AS I WAS NOT GOING TO TRY AND APCH WITH MY ALTIMETER OSCILLATING - SELECTION OF OUR ALTERNATE STATIC SOURCE OR AIR DATA COMPUTER DID NOT CORRECT ALTIMETER PROBLEM. AT THIS TIME WE WERE IN DSCNT AND FO SHIFTED OUR GUIDANCE COMPUTER TO #2 SO FO WOULD BE FLYING ON CORRECT AUTOPLT. I ALSO FELT AND FO ADMITTED SHIFTING FLYING DUTIES IN MIDSTREAM IS SOMETIMES COMPLICATING AS WE ADJUSTED FOR A LOW APCH. DUE TO BWI APCH IN ITS USUAL BACKUP POS, WE WERE #8 FOR THE ILS 10. OUR PRELIMINARY COCKPIT DUTIES AND APCH BRIEFING WERE COMPLETED AS WE DSNDED ON VECTORS AND REDUCED SPD FOR THE APCH. AFTER TURNING ON THE ILS INBOUND, APCH REQUESTED WE MAINTAIN 170 KTS, AND SLOWED. OUR AUTOPLT KICKED OFF 3 TIMES DURING OUR INITIAL GS INTERCEPT, WITH IMMEDIATE PLACEMENT BACK TO ON AND RECAPTURE, WE NOTICED ON TCASII THAT TFC SEPARATION WAS NOW DOWN TO 3 MI AS WE CALLED TWR FOR LNDG CLRNC OUT OF 2000 FT OUTSIDE THE LOM. TWR SAID TO MAINTAIN 170 KTS AND NOT 20 SECONDS LATER OUR OF 1600 FT WE WERE GIVEN TURN TO 180 DEGS AND CLB TO 2000 FT. FO PUNCHED TOGA BUTTONS AND IMMEDIATE PWR APPLICATION SHOT ACFT SKYWARD TO CLB AND PASSED 2000 FT IN TURN. I TOLD FO TO 'MAINTAIN 2000 FT' AND HE FINALLY KICKED OFF AUTOPLT TO RECAPTURE ALT AS WE SHOT BY IT TO 2350 FT. MY ALTIMETER WAS USELESS. THE STANDBY AS ACCURATE. BUT I'M TRYING TO KEEP AN EYE ON FO SIDE AS THINGS SEEM TO GET CRAPPY. APCH SAID NOTHING AS WE RELEVELED AT 2000 FT AND TURNED US OUT TO FOLLOW NEW TFC FOR ANOTHER ILS. TFC AHEAD OF US ON 1ST APCH SLOWED UP AND SPACING BY ATC WAS ABSOLUTELY TERRIBLE. FO MENTIONED ATC DOES THIS A LOT AND CAUSES THEIR OWN PROBLEMS. AS WE RE-INTERCEPTED ILS 10 WE SLOWED TO 150 KTS AND TOLD APCH WE'RE NOT GOING AROUND AGAIN.

Data retrieved from NASA's ASRS site as of July 2007 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.