B757 air carrier flight crew reported a trailing edge flap EICAS malfunction on final approach. The crew performed a go around and returned for a safe partial flap landing.
Synopsis
B757 air carrier flight crew reported a trailing edge flap EICAS malfunction on final approach. The crew performed a go around and returned for a safe partial flap landing.
Narrative
Below is a summary of today's events to the best of my recollection. On approach into ZZZ Descended via the ZZZZZ1 [arrival] then the ILS XXR. I was the Pilot Flying and I configured the aircraft in accordance with FM (Flight Manual) and FOM limitations. The landing checklist was completed at approximately 1;300 AGL we were on Speed established on the LOC and G/S. The autopilot was disengaged around 2;000 AGL. At roughly 400-500 AGL I noticed a master caution sound followed by some vibration. I immediately glanced down at the cockpit indications and realized the flap indicator showed between Up and 1. My thought process was Flaps 1 at VREF speed that's not good. The Captain noticed the same indications and we immediately called the go around at the same time. We followed the Go-Around Profile and I Called Going Around Flaps 20 Check Thrust; Positive rate gear Up Set Missed approach altitude." During the middle of this; the gear warning horn started going off and the flap indications went back to 30. The noise from the gear warning horn was distracting and led to multiple ATC calls being missed. I elected to keep the speed at approximately 150 knots versus speeding up to climb speed on the Go Around profile because the flap indications were Flaps 30; we then noticed a TE FLAP ASYM message; and the plane felt like flaps 30. The Captain then said "lets drop the gear we had 10;500 LBS of fuel;" and we dropped the gear to silence the warning (to our knowledge that was the only option). With the increase in workload and the constant changes from ZZZ Departure combined with missed radio calls from the distractions of the gear horn we decided to [request priority handling]. I got the autopilot on; and the Captain went into the checklist. We ran the checklist which told us if flaps are greater than 20 then land at VREF 20. I bugged the higher VREF speed. We then talked about the differences with the second approach the Captain briefed the flight attendants then we transferred controls. The Captain wanted me to look at the checklist to ensure we got it right. We got revectored for the approach and the landing was successful."
Second reporter narrative
At approximately 400 ft AGL; crew observed flap position indicator move from 30 degrees to approximately one half a degree and stop. EICAS displayed a TE Flap ASYM message with associated cautions. During the go around; when the gear was selected up; gear configuration horn sounded. Flap handle was at 20; flap position indicator varied between .5 and 30; with it eventually setting at 30 degrees. Gear configuration warning was sounding at the beginning of the event to the point ATC and crew communications were extremely hard. FO noted the controls had a roll tendency indicating a true asymmetry; even though the gauges did not show a split. Due to the unknown position of the flaps; [we requested priority handling].
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.