Narrative:

On climb out from ZZZ; I initially noticed TCAS fail light. Switched to other transponder and no luck. First officer began working the problem to restore transponder. At level off; autothrottles were inoperative with no visual/aural warning. ATC was asking verification of altitude and position. Next came a turn to intercept the victor airway on course. LNAV also was not functioning. Had to go to manual navigation. Since first officer is not issued low charts; I pulled out the charts and dialed appropriate NAVAID and course. ATC requested position/altitude several more times. We were very busy trying to work the situation; navigate; and communicate with each other and ATC. Assigned climb to 7000 ft then to 12000 ft. In clouds; precipitation and icing. Asked for higher. Turned aircraft control over to first officer. Checked cabin altitude; pointed to it and commented cabin is good. As we leveled off at FL200; we had a cabin altitude warning horn. I donned my oxygen mask and first officer requested lower. Cabin altitude maxed out at 10300 ft. We were about 100 miles east of ZZZ1 and decided to land there after talking to dispatch and maintenance. At about 50 miles out; I signed off with maintenance and dispatch to concentrate on the approach. We never received the automatic fail light on prsznt panel nor off the schedule descent light. After switching to stby; the cabin was controled for a brief time and then went uncontrolled but we may have caught the cabin since we were descending through lower altitudes at that time. Landing at ZZZ1 uneventful.callback conversation with reporter revealed the following information: the reporter stated the airplane was switching from air mode to ground mode to air mode continuously. Xponders; autothrottle inoperative with no warning. LNAV was not functioning and operated on manual navigation. On leveloff at FL200; had the cabin pressure warning horn. Aircraft descended to a lower altitude and did catch the cabin using manual mode. After the airplane was fixed at the diversion station by company technicians; the airplane was ferried to a company maintenance facility. During the ferry flight the company technicians explained the faulty ground air sensors and targets that failed on the right main landing gear were in bad condition and the wiring was in poor shape. The reporter indicated the technicians revealed that at every heavy check that was accomplished by the company maintenance; these sensors and wiring were replaced and the targets were adjusted. Since these checks have been farmed out to contract maintenance; these components are only replaced if damaged or on test failure.

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Original NASA ASRS Text

Title: A B737-500 IN CLB TO FL200 DIVERTED DUE TO LOSS OF NUMEROUS SYSTEMS; INCLUDING CABIN PRESSURIZATION. CAUSED BY ACFT SWITCHING FROM AIR MODE TO GND MODE TO AIR MODE CONTINUOUSLY.

Narrative: ON CLBOUT FROM ZZZ; I INITIALLY NOTICED TCAS FAIL LIGHT. SWITCHED TO OTHER XPONDER AND NO LUCK. FO BEGAN WORKING THE PROBLEM TO RESTORE XPONDER. AT LEVEL OFF; AUTOTHROTTLES WERE INOP WITH NO VISUAL/AURAL WARNING. ATC WAS ASKING VERIFICATION OF ALT AND POSITION. NEXT CAME A TURN TO INTERCEPT THE VICTOR AIRWAY ON COURSE. LNAV ALSO WAS NOT FUNCTIONING. HAD TO GO TO MANUAL NAVIGATION. SINCE FO IS NOT ISSUED LOW CHARTS; I PULLED OUT THE CHARTS AND DIALED APPROPRIATE NAVAID AND COURSE. ATC REQUESTED POSITION/ALT SEVERAL MORE TIMES. WE WERE VERY BUSY TRYING TO WORK THE SITUATION; NAVIGATE; AND COMMUNICATE WITH EACH OTHER AND ATC. ASSIGNED CLB TO 7000 FT THEN TO 12000 FT. IN CLOUDS; PRECIPITATION AND ICING. ASKED FOR HIGHER. TURNED ACFT CTL OVER TO FO. CHKED CABIN ALT; POINTED TO IT AND COMMENTED CABIN IS GOOD. AS WE LEVELED OFF AT FL200; WE HAD A CABIN ALT WARNING HORN. I DONNED MY OXYGEN MASK AND FO REQUESTED LOWER. CABIN ALT MAXED OUT AT 10300 FT. WE WERE ABOUT 100 MILES E OF ZZZ1 AND DECIDED TO LAND THERE AFTER TALKING TO DISPATCH AND MAINT. AT ABOUT 50 MILES OUT; I SIGNED OFF WITH MAINT AND DISPATCH TO CONCENTRATE ON THE APCH. WE NEVER RECEIVED THE AUTO FAIL LIGHT ON PRSZNT PANEL NOR OFF THE SCHEDULE DSCNT LIGHT. AFTER SWITCHING TO STBY; THE CABIN WAS CTLED FOR A BRIEF TIME AND THEN WENT UNCTLED BUT WE MAY HAVE CAUGHT THE CABIN SINCE WE WERE DSNDING THROUGH LOWER ALTS AT THAT TIME. LNDG AT ZZZ1 UNEVENTFUL.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE WAS SWITCHING FROM AIR MODE TO GND MODE TO AIR MODE CONTINUOUSLY. XPONDERS; AUTOTHROTTLE INOP WITH NO WARNING. LNAV WAS NOT FUNCTIONING AND OPERATED ON MANUAL NAVIGATION. ON LEVELOFF AT FL200; HAD THE CABIN PRESSURE WARNING HORN. ACFT DSNDED TO A LOWER ALT AND DID CATCH THE CABIN USING MANUAL MODE. AFTER THE AIRPLANE WAS FIXED AT THE DIVERSION STATION BY COMPANY TECHNICIANS; THE AIRPLANE WAS FERRIED TO A COMPANY MAINT FACILITY. DURING THE FERRY FLT THE COMPANY TECHNICIANS EXPLAINED THE FAULTY GND AIR SENSORS AND TARGETS THAT FAILED ON THE R MAIN LNDG GEAR WERE IN BAD CONDITION AND THE WIRING WAS IN POOR SHAPE. THE RPTR INDICATED THE TECHNICIANS REVEALED THAT AT EVERY HVY CHK THAT WAS ACCOMPLISHED BY THE COMPANY MAINT; THESE SENSORS AND WIRING WERE REPLACED AND THE TARGETS WERE ADJUSTED. SINCE THESE CHKS HAVE BEEN FARMED OUT TO CONTRACT MAINT; THESE COMPONENTS ARE ONLY REPLACED IF DAMAGED OR ON TEST FAILURE.

Data retrieved from NASA's ASRS site as of January 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.