Narrative:

On climb out; as PNF; at approximately FL180 we received a TCAS fail. After checking the circuit breakers and recycling; the TCAS was still inoperative. Then center reported our mode C had stopped reporting. After cycling and switching both xponders; they were now inoperative. Now; both xponders and TCAS are not working. We received a clearance to climb to FL330 and report vacating FL250. At this time the captain was hand flying and informed me the aircraft wasn't responding to the commands on the autoplt and/or the autothrottles weren't engaging as well. As I was the PNF; he could better report as to the flying qualities and what the plane was or wasn't doing better than me. At about this time; we received the cabin altitude warning horn. I canceled it and checked the cabin altitude; it was near 10000 ft and appeared to be climbing; we then requested lower; declared an emergency; put on oxygen masks; established communications and ran the emergency descent checklist. During the descent; the captain noticed the WX and made the decision to return to ZZZ. Once the plane was stabilized at 10000 ft and 250 KTS headed to ZZZ; we took off our oxygen masks; the captain gave me control at which time I engaged the autoplt; got the WX for ZZZ; set up for the approach and got the landing data; while he tried dispatch and talked to the flight attendants. Center asked us if we were squawking 7700; which we were; but they weren't picking it up; but ZZZ approach was? I believe the outcome was successful and should/could have gone even smoother if: 1) the PA was louder -- the passenger said they couldn't clearly hear the captain's announcements; after we were deplaning. 2) the interphone could have been louder and or clearer so the information and situation could have been more clearly understood and dealt with. 3) we could have communicated with dispatch through voice -- maybe we were too low? 4) we were interrupted countless times by ATC; but later the captain and I understood that they couldn't see our transponder; so we had to continually answer questions; report position; etc. 5) communicating through the oxygen mask and speaker in the plane is more difficult than the sim; in regards to clarity and loudness. I don't believe there were any human factors involved at this time in this event. Callback conversation with reporter revealed the following information: the reporter confirms that a faulty ground/air sensing circuit was responsible for the anomalies reported and was repaired by maintenance.

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Original NASA ASRS Text

Title: PASSING FL180 IN CLIMB; B737 FLT CREW EXPERIENCES NUMEROUS ELECTRICAL MALFUNCTIONS INCLUDING CABIN PRESSURE LOSS. EMERGENCY DECLARED WITH RETURN TO FIELD.

Narrative: ON CLBOUT; AS PNF; AT APPROX FL180 WE RECEIVED A TCAS FAIL. AFTER CHKING THE CIRCUIT BREAKERS AND RECYCLING; THE TCAS WAS STILL INOP. THEN CTR RPTED OUR MODE C HAD STOPPED RPTING. AFTER CYCLING AND SWITCHING BOTH XPONDERS; THEY WERE NOW INOP. NOW; BOTH XPONDERS AND TCAS ARE NOT WORKING. WE RECEIVED A CLRNC TO CLB TO FL330 AND RPT VACATING FL250. AT THIS TIME THE CAPT WAS HAND FLYING AND INFORMED ME THE ACFT WASN'T RESPONDING TO THE COMMANDS ON THE AUTOPLT AND/OR THE AUTOTHROTTLES WEREN'T ENGAGING AS WELL. AS I WAS THE PNF; HE COULD BETTER RPT AS TO THE FLYING QUALITIES AND WHAT THE PLANE WAS OR WASN'T DOING BETTER THAN ME. AT ABOUT THIS TIME; WE RECEIVED THE CABIN ALT WARNING HORN. I CANCELED IT AND CHKED THE CABIN ALT; IT WAS NEAR 10000 FT AND APPEARED TO BE CLBING; WE THEN REQUESTED LOWER; DECLARED AN EMER; PUT ON OXYGEN MASKS; ESTABLISHED COMS AND RAN THE EMER DSCNT CHKLIST. DURING THE DSCNT; THE CAPT NOTICED THE WX AND MADE THE DECISION TO RETURN TO ZZZ. ONCE THE PLANE WAS STABILIZED AT 10000 FT AND 250 KTS HEADED TO ZZZ; WE TOOK OFF OUR OXYGEN MASKS; THE CAPT GAVE ME CTL AT WHICH TIME I ENGAGED THE AUTOPLT; GOT THE WX FOR ZZZ; SET UP FOR THE APCH AND GOT THE LNDG DATA; WHILE HE TRIED DISPATCH AND TALKED TO THE FLT ATTENDANTS. CTR ASKED US IF WE WERE SQUAWKING 7700; WHICH WE WERE; BUT THEY WEREN'T PICKING IT UP; BUT ZZZ APCH WAS? I BELIEVE THE OUTCOME WAS SUCCESSFUL AND SHOULD/COULD HAVE GONE EVEN SMOOTHER IF: 1) THE PA WAS LOUDER -- THE PAX SAID THEY COULDN'T CLEARLY HEAR THE CAPT'S ANNOUNCEMENTS; AFTER WE WERE DEPLANING. 2) THE INTERPHONE COULD HAVE BEEN LOUDER AND OR CLEARER SO THE INFO AND SITUATION COULD HAVE BEEN MORE CLEARLY UNDERSTOOD AND DEALT WITH. 3) WE COULD HAVE COMMUNICATED WITH DISPATCH THROUGH VOICE -- MAYBE WE WERE TOO LOW? 4) WE WERE INTERRUPTED COUNTLESS TIMES BY ATC; BUT LATER THE CAPT AND I UNDERSTOOD THAT THEY COULDN'T SEE OUR XPONDER; SO WE HAD TO CONTINUALLY ANSWER QUESTIONS; RPT POS; ETC. 5) COMMUNICATING THROUGH THE OXYGEN MASK AND SPEAKER IN THE PLANE IS MORE DIFFICULT THAN THE SIM; IN REGARDS TO CLARITY AND LOUDNESS. I DON'T BELIEVE THERE WERE ANY HUMAN FACTORS INVOLVED AT THIS TIME IN THIS EVENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER CONFIRMS THAT A FAULTY GROUND/AIR SENSING CIRCUIT WAS RESPONSIBLE FOR THE ANOMALIES REPORTED AND WAS REPAIRED BY MAINTENANCE.

Data retrieved from NASA's ASRS site as of May 2009 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.