B737NG flight crew reported an upset occurred after encountering wake turbulence on approach to LAX in trail of a B787.
Synopsis
B737NG flight crew reported an upset occurred after encountering wake turbulence on approach to LAX in trail of a B787.
Narrative
3 issues on arrival into LAX:We were given 'cross Goatz at and maintain 16000 ft.' by LA Center. This was set into the MCP and loaded into the FMC while in VNAV. The legs page had a discontinuity between the abeam points in front of Goatz and Goatz; which we closed. At some point in the process; the 16000 restriction at Goatz dropped out of the FMC and neither pilot noticed. Consequently VNAV was programming a descent to the point beyond Goatz (also at 16000 ft.); and by the time we realized it; we were much too high to make the restriction at Goatz. Center was notified and seemed OK with it.While being vectored to Runway 25L by SoCal Approach we were instructed to descend to 2600 ft. At the time we were east of Gaate which has an altitude restriction of 5000 ft. This seemed low; so we asked ATC to confirm the altitude; which he did. We were then cleared for the ILS 25L; but were planning and told to expect the RNAV Y. We corrected the Controller and were subsequently cleared the RNAV Y. 2600 ft. put us below all of the altitude restrictions outside the FAF and seemed too low for our position so we did a slow descent to 3600 and intercepted the VNAV path at Hunda (3600 alt restriction); hence not fully complying with the descent to 2600 ft.The vectors to final were given to us because we were following a heavy 787. We were approximately 6NM in trail of the 787 just prior to the FAF Gigli when the aircraft began to turn left. Both pilots assumed this was LNAV programing a turn for some reason and we focused on the displays. The aircraft continued the left roll and we received a 'bank angle' caution; at which point we called 'upset'; disconnected the autopilot and auto throttles and recovered the aircraft without incident. The assumption was that we hit wake turbulence from the 787; so we reconnected the automation and continued the approach landing beyond the approach path of the 787 but within 3000 of the TDZ.
Second reporter narrative
Missed crossing restriction--plus non standard ATC clearance on approach. Additionally a wake turbulence event on final approach.In ZZZ I loaded the ILS to 25L. Upon viewing the ATIS within ACARS range of LAX I changed the approach to the RNAV Y 25L. When we checked in with LA Center he issued the GOATZ arrival with a non published crossing restriction of 16;000 ft. at GOATZ. The CA (Captain) hard coded the altitude at GOATZ and I confirmed. At some point either before TOD or after beginning our descent the CA realized that there was a discontinuity somewhere in the arrival. He closed the disconnect. While in the descent I was monitoring the VPI and we were in VNAV SPD initially as the automation was slow to begin the descent. About 400 ft. high and still no trend towards VNAV PTH I selected the speed brakes. We were back on path prior to GOATZ. However neither one of us realized that the FMS had deleted the hard coding at GOATZ and was heading for the published 19000-16000 ft. at DIRBY. We did not realize this until about 4 miles prior to GOATZ when both of us saw that we were going to be very high. We notified ATC that we were high; he acknowledged that and we crossed GOATZ at about FL230. We continued rapidly descending and resumed the rest of the arrival as published and instructed by ATC. I am not sure why they do it; but in addition to the non-published crossing at GOATZ; we were issued several descend via but maintain altitudes during the rest of the arrival with LA Approach. They very rarely allow us to fly the arrival as published. This can cause a lot of threats and with the constant threat of the VNAV on the 737; all the changes can result in problems. Unrelated to the altitude deviation above approach issued a strange altitude clearance while on approach to the RNAV Y 25L. We told to fly a heading of 010 out of SLI for spacing behind a 747 (turned out it was a 787). Approach turned us back NW on a vector to join somewhere outside of GAATE. I believe we were at about 5000 ft. ATC cleared us to 2600 ft. We were both questioning that because there is no 2600 ft. published anywhere on the approach. The CA confirmed the altitude with ATC and I selected level change and along with the final turn to join final began descending. As we were on a heading to join the final approach course I reselected both LNAV and VNAV. The airplane descended until reaching 3600 ft. in VNAV PTH. We were outside of GAATE; published 3600 ft. Once the LNAV and VNAV were on track we flew the approach as published in LNAV and PTH. However; just as we both thought the jet was stable on the final approach course; it was very close to the end of its turn to join; it continued to turn left. We both initially thought it was the LNAV getting on course until the turn continued and was leading past the final approach course. About the same time we both asked each other what it was doing the wings started to roll even more to the left. I immediately disconnected the AP and rolled wings level. The CA announced 'Upset'; and I went through the upset recovery steps with the exclusion of disconnecting the autothrottle. The event happened so quickly and was also over very quickly once I disconnected the AP that I never got to disconnecting the autothrottles. I did call out the steps and reacted as necessary with the pitch and roll. Once stable we agreed that it was wake from the preceding heavy.I hand flew us back onto the approach until the automation could be re-engaged. LAX was 1200 OVC at the time and per the FM (Flight Manual) the AP had to be on until the runway visual could be maintained. Once we went through the thin marine layer and had the runway clearly in sight; I manually landed uneventfully.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.