B737 flight crew reported encountering strong up and down drafts due to severe turbulence which resulted in a temporary loss of control during approach.
Synopsis
B737 flight crew reported encountering strong up and down drafts due to severe turbulence which resulted in a temporary loss of control during approach.
Narrative
While on the ZZZZZ. RNAV arrival into ZZZ we had been in contact with ZZZ Approach while descending through FL240 down to 14000 feet then was given to Descend Via" the ZZZZZ which the bottom altitude was 4000 ft for Runway XXL. The Pilot Monitoring and myself had been monitoring the weather during the course of the arrival and had noticed that there was a large build up or a large weather cell that was possibly hovering over the last part of the ZZZZZ STAR. I asked the Pilot Monitoring to ask ZZZ Approach control to see if we could receive a heading to the south of the arrival and try to stay clear of the weather going towards the waypoint that ZZZ Approach wanted us to fly towards. The Approach controller had stated to us that he did not see anything on his radar screen weather wise that would put us into the weather during the arrival but did give us a heading to fly and we would then expect radar vectors for the ILS RWY XXL approach. At the time the Approach controller gave us a heading to fly and then gave us a frequency change to contact ZZZ1 Approach. Upon contacting the ZZZ1 Approach controller he then gave us a heading to fly as well that would set the aircraft up for an intercept course into the final approach course for the ILS RWY XXL approach into ZZZ. The ZZZ1 Approach Controller also noted to us that the previous two aircraft that had just gone into ZZZ reported heavy moderate and light severe turbulence all the way to landing; but were able to land at ZZZ. I as the Pilot Flying on the intercept course was already at Flaps 2 and called for Flaps 5 when we started to encounter moderate turbulence and very heavy precipitation. At that same time we were also given a descent altitude down to 3000 ft which I dialed into the Mode Control Panel Altitude window and used Vertical Speed to bring the aircraft down to 3000ft. At that exact moment we're in very extreme precipitation and the turbulence worsened from heavy moderate to severe and the aircraft went into CWS (Control Wheel Steering) and also went into a drastic bank angle to where the "Bank Angle" annunciation voice was heard. I disengaged the CWS mode and decided to hand fly and at that same time the Pilot Monitoring alerted ZZZ1 Approach Control that we were unable to hold heading to intercept and that we would not be able to shoot the ILS RWY XXL approach anymore . The turbulence at this point was at severe to where aircraft control was very difficult and the updrafts and downdrafts were +/- 2000 feet. At this time as well since we were in Flaps 5 the airspeed went into the red and we over speed the flaps momentarily for at least 5 seconds until the airspeed could get under control again. We told the Approach controller that we could fly heading 090 to head east and when able we would need an altitude to climb to to get us out of the weather. The Approach Controller gave us heading 080 and a altitude to 5000ft. Once able to regain aircraft control fully and automation restored we ended up climbing to 5000 feet and on heading 090. Once we were up to altitude the Approach Controller gave us box radar vectors until we were ready to try another attempt coming back into ZZZ again. The box radar vectors including a heading of 090 and also heading of 270. After a few box radar vectors turns the Approach Controller had informed us that the weather that was over the airport had started to move to the northeast and that the precipitation started to weaken. We both agreed to try to shoot the approach again but this time the Approach Controller recommended that the weather on the side of XXR would be better so we agreed to set up for the ILS RWY XXR approach back to the field. Once the ZZZ1 Approach Controller radar vectored us and also had us descend down to 3000 ft to set up on an intercept course for the ILS RWY XXR I called for Flaps 1 and then Flaps 5 and then again the weather on the intercept course deteriorated and I said we wouldn't be able to continue and once again we decided to not continue and ask for radar vectors to get us out of the severe weather which was extreme precipitation at this point. Upon receiving radar vectors from the approach controller to fly a specific heading and altitude to climb back up which was 5000 ft; we all of the sudden encountered an extreme updraft in excess of 5300 feet per minute and went right through 5000 ft and then the Pilot Monitoring told the Approach controller that we wouldn't be able to hold 5000 ft as assigned and then he gave us a block altitude all the way to 12000ft on a heading of 090. Once we were able to get on top above all the weather at 10500 ft and climbing to hold level at 12000 I transferred controls to the Pilot Monitoring and made a phone patch call to dispatch to make the dispatcher aware of the situation. The dispatcher and I both agreed that once we got to our reserve fuel number and if haven't made an attempt to try to come back into ZZZ that we would divert to the new assigned alternate which was ZZZ1. Once I was done with dispatch I retook controls from the Pilot Monitoring and that this time the Approach Controller alerted us that another aircraft that had been holding as well was able to successfully make an approach and land at the airport but this time it was the ILS RWY XXL. We both agreed that we would try one more time to come into ZZZ and set up for the ILS RWY XXL approach. We were able to successfully execute the ILS RWY XX L approach and landed safely and taxied to the Ramp. Once in the ramp and all checklists were completed I made a logbook entry write up noting that the Flaps had been oversped. I also spoke to maintenance and detailed it to him and he told me that before the aircraft goes out for the next flight that they would do a detailed inspection. I also spoke to the Dispatcher and the Manager on Duty and made them both aware of what had happened. Even though the Pilot Monitoring and myself had both seen the weather on our radar screens that looked very poor and deteriorating we relied on the ZZZ Approach controller that had informed us that the weather from where he was sitting looked ok on the arrival and that it was pushing to the northeast away from where our track would take us. I also agreed to the radar vectors that the ZZZ Approach controller gave us that would take us south of the very bad weather but instead put us right in the middle of another embedded thunderstorm that was not showing up until we were already committed to the radar vectors given. The ZZZ1 Approach controller also had informed us that two previous aircraft that had gone into ZZZ prior to us had reported heavy moderate turbulence all the way to touchdown. We could have delayed our departure for at least 1 hr out of ZZZ2 and had let the weather in ZZZ push through knowing that at our original time of arrival was showing drastic weather conditions forecast for the area. The dispatcher had given us a reroute while we were en route to ZZZ which helped us get to west of the most severe weather but at our time of arriving on the ZZZZZ STAR we could've requested to hold with the fuel we had to hold with while the weather pushed through."
Second reporter narrative
During our descent into ZZZ via the ZZZZZ arrival for runway XXL; we have established communication with ZZZ Approach. We were cleared to descend from 24;000ft to 14;000ft then via ZZZZZ arrival. Noticing deteriorating weather conditions on the arrival path; we requested vectors to the South to avoid the weather; however; ATC advised us the no significant weather has been reflected on his radar on the arrival path; so we continued on the arrival then we would expect radar vectors for the ILS XXL. ZZZ has given us a frequency change to contact ZZZ1 approach. Upon checking in with ZZZ1 approach; we been advised that two aircraft's ahead of us has reported heavy moderate and light severe turbulence. The aircrafts ahead of us were able to land at the airport. While on radar vectors to intercept the localizer inbound to the final approach course; we have encountered turbulence that has progressed from moderate to severe that has caused significant attitude changes and autopilot reverted to CWS. Pilot flying has disengaged the autopilot to hand fly while Pilot motoring was consistently updating PF with path deviations and advising ATC that we are not able to continue on the approach. During this even; the airplane has banked steep enough and bank angle" alert has been activated. During the turbulence recovery; airspeed fluctuations has resulted in a flap overspeed event. We have asked approach for an Easterly heading. Approach has assigned us 080 and 5000 ft then gave us heading to remain in the boxed pattern until ready for another attempt or the weather clears up over final. ATC then advised us that the path for runway XXR has better weather conditions and rain may have weakened. PF and PM agrees to set up for RWY XXR approach for another attempt. As we were giving heading and altitudes to intercept the final approach course for XXR; PF started to configure but once again the weather has started to deteriorate. As a result; we have encountered strong updrafts and downdrafts. PM noticed updrafts up to appx 5500ft/min. PF decided to discontinue that approach and receive. We were initially assigned a heading and 5000 ft. Due to the strong updrafts; we have advised ATC that we would be unable to maintain that altitude so ATC gave us 12000 ft. After clearing the weather; PM suggested that we discontinue the Arrival into ZZZ and head to our alternate airport which was ZZZ1. PM was messaging dispatch as PF was flying and coordinating with ATC. Then; PF decided to phone patch dispatch after transferring radios and controls. After communicating with dispatch; Capt decided to divert to ZZZ1 if no other attempts has been made to return to ZZZ by the time FMC reserve is reached. FO agreed to the plan. As we kept receiving radar vectors; ATC advised us that there is another aircraft that is 12 miles away from the airport attempting the approach and if we would like to wait until they go through the approach to receive any PIREPS from that aircraft. Later; we have received PIREP that the other aircraft was able to safely land uneventful and that the weather has cleared up. We then decided to make another attempt and PM was setting up for the ILS XXL approach. This third attempt; the weather has significantly improved and landed safely without any further events. On the ground; all information has been relayed to maintenance; dispatcher and duty pilot. The biggest cause is that both PF and PM relied heavily on ATC reports even though aircraft radar was showing a deterioration in weather during the approach. We have relied on the vectors from ATC which led us to this event.We could have delayed the flight until weather showed significant improvement at the destination at ETA.Requesting a holding pattern until weather completely improves over the airport. We had enough fuel at that time to do so but we were relying more on ATC reports.We could have trusted what we are seeing with our eyes (deteriorating weather) and what's being displayed rather than completely relaying on ATC reports alone."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.