B737 flight crew reported receiving a Wing Body Overheat message and subsequent cabin pressure malfunction during cruise flight. Flight crew descended and continued to landing at destination.
Synopsis
B737 flight crew reported receiving a Wing Body Overheat message and subsequent cabin pressure malfunction during cruise flight. Flight crew descended and continued to landing at destination.
Narrative
Approximately 30 minutes into cruise at FL360; the left WING BODY OVERHEAT caution light illuminated. Captain ran non-normal checklist which had him turn off the No. 1 Engine Bleed and the left PACK. FO was PF and Captain was PM. FO continued to fly aircraft while Captain ran the checklist. Jumpseater was present on the flight deck. Dispatch was then notified via ACARS after ELB (Electronic Logbook) was submitted. Dispatch then coordinated a phone patch with Maintenance Control. Captain told Dispatch that we were to avoid any icing conditions that would necessitate turning on wing anti ice. Dispatch suggested we remain at or above FL150 until reaching ZZZZZ. Captain also talked with Maintenance Control to ensure the full situation was understood by all and that it was safe to continue to our original destination of ZZZ. After non-normal procedures were complete and conversations with Dispatch and Maintenance Control were ended; all three pilots discussed several things we would do if additional issues arose. These conversations covered several situations - one that happened to occur later in our flight. Approximately 30 to 60 minutes after the left WING BODY OVERHEAT illuminated; the CABIN ALTITUDE warning light illuminated. Upon receiving this warning light; all three pilots donned their oxygen masks and crew communication was established. Seat belt sign was then turned on. The remaining portion of the QRC was ran by the Captain at the same time when the Captain [requested priority handling] with ATC and told them we were initially descending to 10;000 feet MSL and remaining on our current route to ZZZ. Captain also gave souls on board and fuel on board to ATC. ATC was also told that a status update would be given after we completed our checklists and assessed the situation. QRC items 1 through 8 were accomplished. Since cabin pressure was controllable using the manual mode; we then went into the non-normals 2.20 CABIN ALTITUDE. The cabin altitude was able to creep up above 10;000 feet before it was manually controlled and brought down to 5;000 to 6;000 feet. By this time; Captain told ATC that were leveling off at FL150 and continuing to ZZZ for the ZZZZZ arrival and the XXR visual backed up by the ILS. ATC then gave a shortcut to ZZZZZ. Shortly after beginning the descent from FL360 and running the QRC; Captain deviated from the non-normal checklists by turning on the No. 1 engine bleed and the left PACK even though the left WING BODY OVERHEAT non-normal had us turn them off. This helped stabilize the cabin altitude. Upon reaching FL150; the No. 1 engine bleed and the left PACK were turned off so as to prevent any damage from a possible bleed air duct leak. This deviation to the non-normals was the fruit of conversations all three pilots had after the left WING BODY OVERHEAT caution light annunciation; but before CABIN ALTITUDE warning light annunciation. At some point in the midst of these actions; Captain called purser and gave a brief. Afterwards; Captain made a PA announcement to the passengers to assuage their concerns and that all was under control and they could expect a normal safe landing. FO safely landed jet on XXR and Captain taxied to the gate. Once Parking Checklist was completed; Captain talked to all the passengers face to face and thanked them for their cooperation as they deplaned. Afterwards; all flight attendants were debriefed by Captain. Then Captain; FO; and jumpseater debriefed maintenance. They initially thought the No. 2 Engine bleed air valve was faulty which would have cause our depressurization with the left WING BODY OVERHEAT caution light.
Second reporter narrative
During the cruise phase; a master caution occurred and the left Wing-Body Overheat discrete light was illuminated. We followed the associated non normal checklist. The checklist directed us to close the ISOLATION VALVE switch; turn the L PACK switch off; and turn the BLEED 1 air switch off. The wing body overheat light then extinguished. This completed the non normal checklist with the restriction that we needed to avoid flight in icing conditions where wing anti-ice was needed.The captain coordinated with dispatch and Maintenance Control via a phone patch and we determined that our current route of flight was suitable; provided we stayed above 15000 prior to crossing the ZZZZZ intersection on the ZZZZZ STAR.I don't recall the specific timing; but approximately 30 to 60 minutes later; the master warning light illuminated in combination with the Cabin Altitude discrete light and the cabin altitude horn. We donned oxygen masks and accomplished the Cabin Altitude Warning memory items and associated QRC checklist. The cabin altitude remained at approximately 10;000 and the passenger oxygen did not deploy.The captain [requested priority handling] and I initiated a descent to 10;000 feet. During the descent; the cabin altitude became controllable to below 10;000 feet while in manual mode. I stopped the descent at 15;000 feet msl to comply with our earlier restriction to avoid potential icing conditions. While at 15;000 feet the cabin altitude remained controllable in manual mode and we attempted to maintain it at the field elevation of ZZZ. We performed fuel calculations and determined that we had sufficient fuel to continue to ZZZ. The captain once again coordinated with dispatch; the flight attendants; and addressed the passengers over the PA. We continued and landed at ZZZ normally with no further issues.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.