B737-700
Flight Crew Last 90 Days 303
Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types
Aircraft Equipment Problem Dissipated; Flight Crew Returned To Clearance; General Maintenance Action
Weather; Human Factors; Aircraft
While cruising at FL330; I noticed my altimeter climbing almost 300 feet and my airspeed rapidly falling off.  I disconnected the autopilot to ensure no loss of aircraft control.  During this period; I confirmed we had not lost any engines and cross checked the Captain's instrument panel during my descent back to FL330.  I noticed the Captain's instruments still read at altitude and on speed so we elected to have the Captain fly the aircraft while I ran checklists.  We contacted ATC and they reported not seeing any deviation but we requested descent out of RVSM airspace as we had disconnected the autopilot and had conflicting readings on altitude and airspeed. In the descent to FL270; we ran several checklists; Airspeed Unreliable; Probe Heat; IAS and ALT Disagree; and the EEC Checklist as the engines had also reverted to the ALTN mode.  Upon reaching FL270; the instruments agreed and we finished the flight with no more problems.
Cruising at FL330 with the autopilot engaged; the First Officer (pilot flying) saw his altimeter suddenly start to indicate a climb and his airspeed indicator indicating a rapid loss of airspeed. As pilot monitoring; I noticed an 'altimeter disagree' warning on the PFD (Primary Flight Display).The First Officer immediately disengaged the autopilot; lowered the nose; and pushed up the thrust levers in response to what he perceived as a loss of airspeed in a climb. I crosschecked my PFD with the standby instruments and saw that we were now descending to about 400 feet below FL330 and accelerating toward VMO. I intervened; took control of the aircraft; and brought it back to level flight and cruise airspeed. We queried Center about what altitude he showed us at and the Controller verified that we were at FL330. He had not seen any indication of our descent. We ran all the appropriate checklists; including the EEC Alternate Checklist; since the EEC's on both engines had gone into the soft alternate mode. We coordinated for a descent below RVSM airspace and proceeded to destination; where the aircraft was taken out of service for complete check of the pitot/static and air data systems.Our current critical action procedure for unreliable airspeed begins with Aircraft Attitude/Thrust.... Adjust. We might want to put the last step; 'Mach/Airspeed Indicators...Crosscheck' first; to avoid a situation where the pilot flying makes inputs on erroneous data.
B737-700 flight crew experiences loss of airspeed indication and erroneous altitude indication during cruise a FL330. EEC had switched to soft alternate. The Captain's instruments are determined to be correct and descent out of RVSM is initiated.