B787 first officer reported resolving pressurization system malfunction during cruise.

Attributes
ACN	1612332
Time
Date	201901
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B787-900
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Pneumatic System Control
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 137.25 Flight Crew Total 11289.93 Flight Crew Type 2095.00
Events
Anomaly	Aircraft Equipment Problem Less Severe

Narrative:

Our left pack was deferred and meled for several days before flight. The captain accepted the aircraft with the deferral. Approximately 5 hours into the flight; we climbed to FL370. Shortly after reaching FL370; we heard several surging sounds from the pressurization system and we felt a shutter once in the airframe. We called maintenance and decided with their explanation of the deferral; we would try FL360. While at FL360 we felt no more shutters in airframe and heard no more surges in pressure. The captain thought it was prudent; and the safest course of action; to limit our altitude to FL360 or lower; for the rest of the flight. We continued the flight with no further issues and we wrote it up in log book.

Original NASA ASRS Text

Title: B787 First Officer reported resolving pressurization system malfunction during cruise.

Narrative: Our left pack was deferred and MELed for several days before flight. The Captain accepted the aircraft with the deferral. Approximately 5 hours into the flight; we climbed to FL370. Shortly after reaching FL370; we heard several surging sounds from the pressurization system and we felt a shutter once in the airframe. We called Maintenance and decided with their explanation of the deferral; we would try FL360. While at FL360 we felt no more shutters in airframe and heard no more surges in pressure. The captain thought it was prudent; and the safest course of action; to limit our altitude to FL360 or lower; for the rest of the flight. We continued the flight with no further issues and we wrote it up in log book.

Data retrieved from NASA's ASRS site 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.