2025-01 · NASA ASRS report 2202978
B737-800 flight crew reported loss of hydraulic pressure and malfunctioning yaw damper. After an oil bypass valve failure indication the flight diverted to a nearby airport.
The first occurrence of this event; which ultimately aided us in making the decision to divert to ZZZ began on our climb out at FL240; for FL320. The FO and I (CA) received an amber alert message for the ENG 2 Hydraulic Pump; at this time; I stated 'My Aircraft' followed by identifying the caution message that was received. Confirming that the aircraft control was safely under control; the FO punctually referenced the associated QRH procedure for 'Hydraulic Pump Low Pressure.' The QRH procedure required for the associated HYD Pump Switch (ENG 2) to be placed in the 'OFF' position with no further action. Understanding the notes section for this particular checklist; we were aware that it may be possible to intermittently experience an illumination of the LOW PRESSURE light for the remaining associated electric motor-driven hydraulic pump - for this note; the FO recommended we leave the hydraulic synopsis page displayed so that we can actively monitor and verify that we had consistent; positive hydraulic pressure for the B system. I believed that was a great idea; and we did just that. An initial eAML entry was made for this issue. Continuing along at FL320 sometime between 2 and 2.5hrs into the flight; near the ZZZZZ waypoint; we would then receive an amber master caution and recall message; this time for System B ELEC 1. 'My Aircraft' was then stated by myself as the PF; and we acknowledged the message; understanding that this was already made aware to us as a possibility referencing the Hydraulic Pump Low Pressure QRH. We would moments later notice that our System B hydraulic pressure and quantity indicated on the synopsis page would begin to rapidly drop to zero. At this time; once the pressure neared zero; the aircraft's Yaw Damper disengaged. We were just approaching the Location X at FL320 and with reports of mountain wave activity being in the area; while we were not experiencing the mountain waves; it was a high possibility that controlling the aircraft could become seemingly more difficult. I (the PF) continued to fly the aircraft with the autopilot (CMD A) on. Initially the ride at FL320 was not rough in any degree; though right before we began to reference the QRH procedure for 'Loss of System B;' we began to experience light turbulence which then made controlling the aircraft in a smooth; manner more difficult as the yawing motions began to increase. Doing our best to counteract the yawing motion; the turbulence began to worsen over the mountains; we knew by referencing the FMS Plus application along with reports in our area; that the winds and rides at the lower flight levels were much better; which is when I asked the FO to request a descent to FL280 with ATC. We were granted this request. At FL320; the conditions began to worsen regarding the rides; which ultimately disengaged the A/P; FL280 was confirmed on the MCP and an initial descent at a smooth rate was attempted. This was done by opening our speed window; selecting .75; and the FO inputting a -700 FPM decent rate via vertical speed. Understanding that maintaining the aircraft's speed was not an issue; the primary focus was to operate the aircraft as safely as possible so that the flight path conditions would not worsen; thinking about our FA's and passengers in the cabin. The descent was then initiated; and the yawing motions began to increase with the turbulence we received; the autopilot kicked off as a result following a call from the #1 FA inquiring about the rides. Task saturation began to increase regarding maintaining safe and positive control of the aircraft; 'My Aircraft' was again stated by myself; and I asked the FO to inform the FA's to take their seats and that we will get back to them in a timely manner. That was done; and with the seatbelt sign on; the passengers all took their seats and the FA's began to occupy their respective jumpseats for their safety. The FO then brings his focus back to the situation that we were experiencing after speaking with the #1 FA and immediately began aiding me in monitoring our descent rate along with the volatile yawing motion. It seemed that we were able to maintain a steady descent rate and after 18 seconds of hand flying; I reengaged A/P CMD A to help reduce our workload. 11 seconds later as the yawing motions began to increase again; the A/P was then kicked off again. Reverting back to hand flying; positive aircraft control remained established; 23 seconds later; the autopilot was then reengaged; this time with a command input to descent at -500 FPM; then the autopilot shortly after disengaged once more. By this point I began to smoothly lower the aircraft's pitch to descend at a faster rate to get out of the turbulence at initially -2550 FPM at FL315 then by FL306; the turbulence smoothed out well and the descent rate was transitioned to -500 FPM at FL300 which the A/P reengaged; for its final time. We then continued a stable descent to FL280; and once we leveled off at FL280; maintaining 280kts (.75) a transfer of the flight controls and radios was made to the FO so that I could speak to the FA's; bring them in the loop as to what was going on and to ensure that they were safe. The FO said; 'My Aircraft' and my conversation with the FA's were made. They were fully safe; acknowledged that they were in their seats; and I informed them that I will call them back once we ran the QRH that was required and to fill them in on a plan that Dispatch; the FO and I developed. Once I brought my attention back to the Flightdeck; the FO did a great job with maintaining safe and positive control of the aircraft as well as informing me that no changes were had. Now that the plane was fully stable at FL280 and we knew that the FA's were safe; we then ran the QRH procedure of Loss of System B. This QRH after following the correct steps in order; we concluded that a flaps 15 landing via alternate flap extension would be required. Though the aircraft was in a stable position and the QRH procedure did not recommend a diversion; I wanted to fill the dispatcher in on the situation to get his input as well. The FO maintained positive control of the aircraft; and using the Crew Central Application; I made a phone call to Dispatch Desk XX. Speaking to the dispatcher and filling him in on our situation; we discussed options of a precautionary diversion but ultimately figured that given our aircraft was able to be safely operated; diverting to ZZZ1 (We were roughly 250 nm NE of the airport) would have not be a good option as the winds were thoroughly gusty there; and landing the aircraft with an inoperative yaw damper in gusty conditions could introduce new threat potentials that neither the FO or I were willing to make. This conclusion was also the same for both ZZZ2 and ZZZ3 as well and we were all in agreement with this idea. The next topic the dispatcher and I discussed was fuel. Knowing that continuing our flight to ZZZ4 at FL280 where the rides would remain smooth and that the weather reported at ZZZ4 was VFR with winds less than 10 knots; landing in ZZZ4 with 6.9 LBS of fuel would still give us the option of being able to divert to ZZZ5 or ZZZ6 if for some reason we could not land at ZZZ4. Now the decision to continue to ZZZ4 was agreed upon; the Dispatcher and I further concluded that [requesting priority handling] was appropriate so that we could 1) Receive priority to ZZZ4; reducing the chances of any sort of route vectors that could compromise our arrival fuel and 2) Given that we would be executing a partial flap landing associated with this hydraulic malfunction. The [priority handling was requested]; the nature of our issue; fuel and souls on board were given to ATC; the FA's were made aware of the plan that the Dispatcher; the FO and I came up with. The FA's were then briefed following the guidance of the Non-Routine Landing Considerations Checklist. Once this was all completed; the FO and I then noticed that we had an 'Oil Filter Bypass' message illuminated for ENG 2. This then caused us to reference the associated QRH procedure for this message. Following the guidance of the QRH; the A/T were disconnected; thrust lever 2 was confirmed and then slowly idled. The Oil Filter Bypass amber message remained illuminated which then led us to the completion of the Engine Oil Filter Bypass QRH and to proceed to the 'Engine Failure or Shutdown Checklist.' Understanding that single engine operations for imminent and the workload between the crew and I will be further increased; the FO and I both were fully aware that we needed to ensure we handle this situation in every way that we've training for; in alignment with SOP's. Prior to these events happening; the FO and I ate our crew meals and now being more than halfway through our flight; the FO expressed his urgency for needing to use the lavatory. Understanding the complexities of our situation and the workload to follow; the exchange of flight controls back to myself was made and the FO made a call to the #1 to set up a keep lavatory break for just himself. I much rather preferred the FO to take care of himself in this manner; so when it came down to doing all the tasks associated with this developed [priority handling]; the FO would have more opportunities of remaining in the 'Green' than if he didn't use the restroom. This also served as a great opportunity to brief the #1 FA once he replaced the FO in the flight deck. Once the #1 FA entered the flight deck; I informed him of our further developed issue; and once again briefed him in accordance with Non-Routine Landing Considerations Checklist and not the briefing. Once the FO returned to the flightdeck; ATC was updated on our new [priority handling] of having to shut down our ENG 2; we needed to descend below at least FL210 and that we will get back to ATC with a plan. We were cleared to I believe FL200 and that descent was initiated so that when we shut down our ENG 2; we'd be at a safe altitude to operate. The FO ultimately regained positive control of the aircraft by acknowledging 'My Aircraft;' and the QRH procedure for 'Engine Failure or Shutdown' was accomplished; concluding that a restart will not be accomplished. Once the aircraft was stable; we needed to formulate a new plan in determining what the nearest suitable alternate would be. Knowing the resources that our Dispatchers have access to with their ability of being such huge assistance to us from the Dispatch; the FO continued to maintain control of the aircraft and now the radios as I attempted to contact via the Crew Central application. Unfortunately to phone call to dispatch desk XX was unable to go through a few attempts; I brought my focus back to the FO to ensure that plane was still operating well and updates from ATC. After it was indicative that we were both in the green; we began to look for a suitable diversion ourselves. Discovered that ZZZ weather was the best; VFR; stable winds below 10 knots; two 12;000ft runways; and we made the decision to go there. A message to dispatch was then sent via ACARs informing them of our developed situation being single engine because of the Oil Filter Bypass and that we were going to ZZZ. Dispatch replied with; 'copy' and began to do their best with coordinating our diversion; providing us with the appropriate updated arrival weather; informing the ZZZ station etc. Continuing now with our One Engine Inoperative Checklist; using the B737 Land App; the required landing distance numbers were run for both the Loss of System B and for One Engine Inoperative. Loss of System B required a landing distance of 6;796ft for 'Dry' conditions; the One Engine Inoperative data required a landing distance of 5;900 ft; we chose the conservative approach; by using the Loss of System B required landing distance as governing. The FO crossed checked my work and our numbers both matched. The FO continued to fly the aircraft as I (CA) did FMC box work; loading up our approach;
During flight we encountered several mechanical issues resulting in a diversion to ZZZ. The first happened during the climb around FL240. We got a caution light for ENG 2 hydraulic pump low pressure. We went through the QRH and it had us turn off the associated pump switch. We had also opened the system hydraulic page to to confirm that we still had system pressure and adequate fluid. Those indications still appeared normal. The captained entered the write up in the AML and we continued.Around 2.5 hours into the flight we received another master caution. This time it was showing both electric and engine pumps for SYS B. We then saw the hydraulic quantity rapidly deplete to zero. A few moments later the yaw damper disengaged with the loss of SYS B. We began a descent to lower altitude with smoother rides with potential mountain wave predicted ahead at higher altitudes. In the descent we did pick up some turbulence and the captain had turned off the autopilot and had to attempt to reengage it a couple of times during descent while I coordinated with ATC and pulled up the QRH. Once level the I took the controls and we went through the QRH. The Captain also informed the flight attendants and called dispatch to coordinate with them. Between all of us we opted to continue for ZZZ4 because the airports around were high elevation with gusty winds and the QRH did no recommend landing at the nearest suitable airport. We informed ATC of the issue and [requested priority handling] to assist with priority handling.Not long after completing those things we realized the Oil Filter Bypass caution was illuminated. We ran the QRH for that procedure; which had us pull the thrust lever back to see if the message would extinguish and it did not. Then it led us to shutdown the engine. After that was done we informed ATC of the new issue and we decided to divert to ZZZ. The weather was pretty calm there and it was around 200 miles ahead of us. On the way in we prepared and discussed factors such as terrain; single engine missed approach; as well as comparing both system failure landing data. The HYD SYS failure resulted in a longer distance required so we used that. The runway at ZZZ provided more than enough distance. Once we landed we had [priority handling] vehicles check us out and they confirmed the right engine was leaking fluid on the runway. We discussed that we believe it is just hydraulic fluid and once the [priority handling] vehicles gave us the OK; we continued to the gate. Once at the gate we shut down the aircraft; completed the write ups and filled in local station and maintenance personnel that came to the flight deck.Cause: A couple of mechanical failures. Everybody we worked with was professional and gave us the support we needed. While there is always room for improvement from us as you look back; our training and professionalism allowed us to work together; run the procedures; and use our resources to get the passengers safely to the ground.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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