B737 flight crew reported multiple equipment failures during descent to land.
Synopsis
B737 flight crew reported multiple equipment failures during descent to land.
Narrative
During descent into ZZZ; the Autopilot kicked off and we noticed the FLT CONTROL master caution light illuminated due to a couple of lights illuminated on the overhead panel. I continued to fly the STAR into ZZZ while directing the First Officer (FO) to run the non normal checklists. While configuring for the approach for the ILS XXR I slowed down to configure and eventually called for gear down and flaps 15. It was then that I noticed no flaps had extended. I immediately directed a go-around. While on the go-around to 5;000 feet we requested delay vectors and [requested priority handling]. We were given holding instructions at ZZZ VOR but could not get it into the box so we continued with delay vectors. Once stabilized at 5;000 feet I gave the aircraft to the FO and took a moment to review what we had and what he had done. I was in the process of looking for the appropriate flap non normal procedure when I happened to pull up the hydraulic system page and noticed that we had lost the B hydraulic system. It was during this time that I managed to get a note off to Dispatch about the problem and that we had [requested priority handling]. I was also able to finally talk to the flight attendants and the make a quick PA to the people. I ran the loss of B Hyd checklist and reviewed this with the FO.Once he was comfortable with the remainder of the checklist; we swapped controls and requested the ILS to XXC at ZZZ. Approach had been calling the ceilings variable between 250 to 400 feet. I hand flew this approach due to another system deferral. We were able to extend the flaps using the Alternate Flap master switch and landed uneventfully on XXC. I cleared the runway at Taxiway 1 then stopped so the emergency vehicles could look us over. We were towed to Gate XX after being cleared by ZZZ fire rescue.We were dispatched with an FMC inop with low ceilings expected in ZZZ. Our alternate was ZZZ1; which was legal but would deteriorate later in the day. We had the initial problem in a critical phase of flight and had fuel on board of 10.4 when we [requested priority handling] with a bingo of 7.5 to get to ZZZ1. I wanted to get the checklist completed and shoot an approach while we still had alternate fuel and options.
Second reporter narrative
I was the pilot monitoring on flight XXXX and the flight was uneventful until we reach approximately 18;000 ft. Captain and I discussed turning on engine anti-ice for icing condition that was approaching; and Captain reached up and placed the engine anti- ice to on. As we descend through approximately 8;000 ft; We received an FMC message stating that temperature exceeds 10 degree while the engine anti-ice was on. As I was pointing out to the Captain about the anti ice message; Approach started giving us vectors to final for Runway XXR. After verifying the icing condition doesn't exist anymore; I reach up were I believed the engine anti ice switches were and place them in the OFF position at the same time reading back approach instructions and executing them in the FMC Since it was below 18;000 ft. As we were on 10nm final at ZZZZZ fix we received a master caution light for Flight controls. I immediately looked up and saw the Flight control light illuminated as well as the Pressure Differential and yaw damper. Shortly after the Autopilot B disengaged by it self. Due to an MEL; the Captain elected to fly this leg on Autopilot command B; as an extra caution to make sure the airplane is on the correct course. Captain immediately took manual control and requested I reference the QRH non normal checklist for Feel Differential pressure. After completing the checklist; Captain requested that I reference the QRH for YAW damper light. I went back to the Flight Manual (FM) Non normals and did Yaw damper checklist. checklist directed me to place the switch back ON and to wait and see if the light extinguish. The yaw damper light did in fact extinguish; and I completed the Yaw damper checklist. At that point the Captain requested to start configuring the airplane for landing. As I selected flaps 5 the master caution light illuminated for flight controls again and I immediately identified the caution to the Captain; at the same time as I looked up at the overhead panel I noticed the yaw damper light illuminated again; but this time it was accompanied with 'low pressure' light for hydraulic B; and this was the first time this has illuminated; and no hyd caution annunciator . At that point we also noticed that the flap indicator didn't move or change and stayed at zero. The Captain decide the best course of action was to execute a go-around to trouble shoot. We executed the procedure for the go around and inform ATC about the go around and ask for vectors. After we leveled off the Captain gave me the control and radios while he performed the non normal checklist for 'low pressure' of Hydraulic B. He completed the Loss of system B checklist. After he completed the checklist we transferred the flight controls and I ask for vectors to Runway XXC ILS approach and landed safely. After we got back to the gate we debriefed it on what went well and what could have gone better.Later during the day; the Captain spoke with Maintenance and after a quick review they didn't detect a hydraulic leak or failure. However one possibility that could have caused the loss of hydraulic B; was the accidental placing of both Hydraulic B pump switched to the off position.Due to the proximity and similarities of the engine anti ice switches with the hydraulic B switches could have led to the mistake; also with all the distraction due to weather; turbulence at the critical times; could have Lead to mistakenly turning off the Hydraulic B pumps.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.