Date: 201502
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
ATC / advisory: TRACON ZZZ
Aircraft component: Pressurization Control System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Illness / Injury
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was scheduled to fly with a student transitioning from the A320 First Officer (FO) to B737 FO.  The student called in sick and the new FO was a short call on reserve. We were 29 minutes late off the gate due to an ACARS issue that was effecting data flow system wide.  We were holding for hard copies of weights; take off data and runway data when the system came back on line slowly. Normal taxi out and take off except we requested anti-ice on for takeoff due to snow on runway still.After take off and on the climb out we experience a pressurization malfunction. The cabin 'altitude horn' sounded around 13;000 feet in the initial climb out. We reached an altitude of about 14;500 feet as we declared and emergency and where issued a decent to 10;000 feet by ATC. Our 'CABIN ALT' and 'DIFF PRESS' were fluctuating wildly up and down.  Level at 10;000 feet the DIFF PRESS gauge showed 8.6 PSI and a CABIN ALT of 27;500 feet. The Cabin Alt and Diff Press gauge was of no use but we were able to control the CABIN CLIMB gauge with the manual position of the pressurization controller and toggle switch.After we complied with the ORH procedures we made the decision to return. Our aircraft state presented a 'Altitude Horn with forward panel  light' followed by a Pressurization 'Auto Fail' light on both AUTO and ALTN modes and an 'Off Schedule' decent light.  On the return it was discovered the Equipment Cooling Exhaust 'OFF' light had come on too; for both normal and alternate positions.  We never got to make a pilot logbook write up due to maintenance so quickly taking the logbook off the flight deck.  They said that they would handle that specific write up when I told them I had not put it in the logbook yet.Upon discussions with flight attendants it was decided to have EMS services available at the gate upon our return.  The Flight Attendants (FA) said the cabin had become quite hot with several customers complaining about their ears and would like EMS to meet us. The FA's were given the T.E.S.T. and updated several times as well inbound.  Several PA's to the customers from the flight deck and FA's positions where made.We requested a 15 mile final to the ILS in visual conditions to allow for a slow and gradual decent to the airport.  The approach and landing where uneventful.  We had to wait for our gate due to it being occupied.  Ramp did mention that the EMS crews were already at the gate; so they decided to hurry the Aircraft on the gate off and made us wait for a few extra minutes.


Second narrative: I was a reserve called at XA00 for a short call. I arrived at the gate an hour prior to departure. I did the preflight which was uneventful. Upon entering the cockpit I started my duties for setting up the aircraft but noticed that the aircraft was not loading the information through ACARS properly. I advised the Captain of this and said I would load the box manually while he discussed the problem with dispatch. Dispatch informed us there was a company wide computer problem and that they were working on it. After a period of time ACARS started functioning properly and we were able to push slightly late. Taxi and takeoff were uneventful but the captain and I decided to use engine anti-ice for the takeoff since the runway still had patches of snow on it. On the climb out passing roughly 14;000 feet the cabin altitude warning sounded. Upon looking at the gauge it made no sense since it was gyrating between a cabin altitude of 7;000 feet and 35;000 feet and a cabin differential which was moving up and down constantly. We immediately decided the best course of action was to stabilize the cabin and declare an emergency. I immediately started a slow descent to 10;000 feet from 14;700 to keep the cabin reasonable while the captain pulled the QRH turned the pressurization switch to man and ran the appropriate checklists. Following the QRH procedures would only stabilize the cabin in Manual mode as the alt pressure gauge was giving an erroneous reading of diff psi 8.7 with a cabin alt of 23;500 feet and an actual plane altitude of 10;000 feet. We both decided that the best course of action would be to immediately return. ATC agreed and we were given priority handling for vectors to the ILS. At this time we were notified by the flight attendants that some passengers were experiencing discomfort with their ears and head. We then asked for a 15 mile final turn in so as to descend at a slow rate for cabin safety and comfort and notified ATC to have paramedics meet us at our gate. We finished the appropriate checklists and landed uneventfully. Even though we had to wait a few minutes for our gate to open up once at the gate we were met with the paramedics and all passenger and crew who wanted treatment were taken care of.


Synopsis: B737 flight crew experiences a cabin altitude warning horn passing 13;000 feet during climb with the pressurization control panel displaying false indications of cabin altitude and differential pressure and actual cabin altitude oscillating up and down. Pressurization is controllable in manual but the crew elects to return to the departure airport due to passenger ear problems.