DC10-30 CREW WAS DISPATCHED INTO TERMINAL AREA ICING CONDITIONS WITH #3 PNEUMATIC SYS MEL'ED INOP; AND WHILE ON APCH HAD AN ADDITIONAL PNEUMATIC SYS FAILURE.

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ACFT DISPATCHED OUT OF OAK WITH #3 PNEUMATIC SYS INOP. EWR APCH WX SUCH THAT ENG AND WING ANTI-ICE REQUIRED FOR APCH. TALKING TO EWR APCH; BEING VECTORED AND DSNDED FOR AN ILS TO RWY 22L. LEVEL AT 4000 FT. GIVEN A DSCNT TO 3000 FT AND TURNED TO A NEW HDG; WITH A CLRNC OF 'ACR X; TURN R TO A HDG OF XXX POS XXX; MAINTAIN 3000 FT UNTIL ESTABLISHED. CLRED FOR THE ILS RWY 22L.' WE ACKNOWLEDGED SUCH. PNF (CAPT) SET; ARMED; AND CONFIRMED 3000 FT AS PER SOP WITH PF (FO). AS THROTTLES PULLED BACK FOR DSCNT TO IDLE; PNEUMATIC SYS #1 FAILED. SO ADVISED CAPT; PHASE 1 PROCS COMPLIED WITH AND AN ALTERNATE SOURCE OF PNEUMATICS FOR THE WING ANTI-ICE WAS IN THE PROCESS OF BEING ESTABLISHED. CAPT WORKING WITH SO (AS PER SOP) TO ENSURE SUCH. COINCIDENTALLY; EWR APCH GAVE US A FREQ CHANGE. AS CAPT TURNED AROUND TO DIAL IN NEW FREQ; I GLANCED AT THE FRONT INST PANEL AND SAW THE ALTIMETER AT APPROX 2750-2700 FT. IMMEDIATELY ADVISED THE FO; HE CORRECTED WITHOUT DELAY BACK TO 3000 FT MENTIONING THAT THE AUTOPLT MUST HAVE NOT AUTOCAPTURED THE PRESELECTED ALT. WITHIN A FEW SECONDS; WE CAPTURED THE LOC. UNEVENTFUL ILS RWY 22L TO EWR AND SUBSEQUENT LNDG. EWR APCH NEVER MENTIONED ANYTHING ABOUT OUR ALTDEV. RELEVANT FACTORS -- ACFT DISPATCHED WITH 1 PNEUMATIC SOURCE INOP; THEREBY MAKING THE LOSS OF A SECOND ONE QUITE SIGNIFICANT; ESPECIALLY WHEN WING ANTI-ICE WAS REQUIRED FOR LNDG. HIGH WORKLOAD TIME COMPRESSION WHEN ALL HAPPENS AT ONCE. LOSS OF PNEUMATICS; CLRNC TO DSND; HDG AND FREQ CHANGES; CLRNC FOR APCH. CAPT WORKING WITH SO AS PER SOP AND IN ACCORDANCE WITH FOM AND AIRPLANE FLT MANUAL TO ENSURE RESTORATION OF WING ANTI-ICE. NEW ALT SET ARMED AND CONFIRMED BY PNF WITH PF BEFORE ACFT EVER LEFT 4000 FT. TOO MANY DISTRS ALL AT ONCE. CAPT RELIED ON FO AS PF TO DO HIS JOB! CREW HAD A POSTFLT DEBRIEF; ALL IN CONCURRENCE WITH EVENTS. SUPPLEMENTAL INFO FROM ACN 575474: DURING DSCNT IN IMC; FO FLYING ACFT; ON AUTOPLT DSCNT TO ASSIGNED ALT; 800 FT PRIOR TO ALT; PNEUMATIC SYS MALFUNCTIONED; ACFT LOST PRESSURIZATION AND WING ANTI-ICE IN ICING CONDITIONS. WHILE SO RECONFIGURED SYS TO REGAIN WING ANTI-ICE; AUTOPLT FAILED TO CAPTURE AND LEVEL OFF AT ASSIGNED ALT. FO ARRESTED DSCNT AT 2700 FT MSL AND RETURNED TO ASSIGNED ALT.