Date: 201512
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Flight phase: Descent
Airspace: Class A ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Human factors: Distraction; Fatigue; Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: Somewhere between FL250 and FL180 the Right Pack light came on. First Officer was Pilot Flying (PF). He grabbed QRH because Captain was making HF radio call. QRH said: choose warmer TEMP on auto-temp switches; then push 'Trip reset' button [overhead the F.O.]. FO did this whilst Captain was distracted; then continued with Pack checklist. Because the PACK light was still illuminated; First Officer turned RT Pack switch OFF and closed the isolation valve. Continued items of Pack checklist on QRH without input from Monitoring pilot. At some point below FL150 Press controller switched to Manual; valve moved towards OPEN. The Cabin warning horn+light ON when acft passing FL145. Horn/light went out 25secs later; acft passing 10;000ft. Capt called Flt Attds quickly briefed them to prepare cabin to land. PA to Passengers to remain seated; cabin air safe to breathe. Called Airport Advisory freq with position and flight path and Runway winds request. Completed Approach + landing checklist. Normal landing. Normal taxi in/parking.


Second narrative: We were approaching our TOD-Top of Descent. I pressed the RE-CALL on my side and was going to ask for the Approach Descent Checklist. On the RE-CALL there was an Air-Condition light and a PACK light on the over head. At that same time we received a HF call. So we had several chimes sounding as well. The Capt responded to the call on HF. I took the initiative and pulled out the QRH. I looked up in the QRH the issue regarding a PACK light for the 800/900. I followed the QRH for the PACK light. What became confusing was when it said to press the TRIP RESET button. Vs asking if it cleared when pressing the MASTER CAUTION. I performed the QRH;...A Single PACK light stays illuminated: ISOLATION VALVE switch ....Close PACK switch (affected side)...OFF. More confusion on my part in reading the QRH. I continued to [next] step after reading the Note. I also; just as a reference; looked at the 700 PACK light QRH. It says if light stays illuminated; press TRIP RESET. Even if still on; it says Continue Normal Operation. Back to the 800/900 if the light extinguishes it says 'Continue Normal Operation'. QRH does not state to check the difference. I became focused on the TRIP RESET vs. a MASTER CAUTION Reset. So I then continued with the QRH;..'Descend to Lower Alt' which we were already doing. Speed 290kts or more. Went to [next] step since we were above 10;000. From there the cabin altitude caught up with aircraft altitude. We were just above 14;000. Horn came on; masks dropped. I donned my mask and continued descent. Captain was establishing communication with the FAs. We passed through 10;000 feet shortly after. Performed the approach checklist. Landed normal with out further incident. No emergency was declared as we were close to [destination] already below 10;000 and plane was secure. We were in a Non-Radar environment and there is no control tower. But as a standard event; the fire station and Fire Truck are always on standby.Once on the ground [we] advised the mechanic. He read the check list and had questions as to why it was worded the way it was. The mechanic said the person he spoke with at [maintenance] saw and agreed how I ended up where I did in the QRH. The mechanic re-stowed the masks and did a BITE test. There were errors noted in the system. The plane was re-dispatched with no further issues.


Synopsis: B737 flight crew reported the aircraft became depressurized following confusion while running the QRH procedure after receiving air condition and pack lights near top of descent.