B767 flight crew reported receiving a LE SLAT ASYM message after takeoff. Flight returned to departure airport and landed safely.
Synopsis
B767 flight crew reported receiving a LE SLAT ASYM message after takeoff. Flight returned to departure airport and landed safely.
Narrative
After takeoff; feeling good about life; we selected the flaps from one to zero; and BAM!; the airplane hit us with an LE SLAT ASYM EICAS; because why not? Instead of panicking; we took a deep breath; accepted our fate; and decided to level off at FL180; keeping the speed under 250 knots like the responsible adults we pretend to be.The FO; being the checklist wizard; whipped out the Non-Normal Checklist; and we followed it like good pilots do. Meanwhile; we found ourselves in the middle of nowhere; over water; playing an impromptu game of 'Who Wants to Be a Relay Station?' with other aircraft since we were out of VHF contact. Thankfully; we still had communications; so we phoned a friend--aka the company--because misery loves company. Fuel status: 60;000 pounds. Plenty for a dramatic return.After some back-and-forth with the company; we agreed ZZZZ was the place to be. But here's where it got interesting: We weren't entirely sure what kind of landing configuration we'd end up with; so we dusted off the landing configuration charts and did some quick math for each flap configuration. Yes; pilots do math; sometimes. Numbers in hand; we turned toward ZZZZ; hoping for the best.Now; the fun part: ZZZZ is high; and high-elevation landings are not the place to casually try a no-flap landing. So; we played it smart--continued toward the airport; cautiously configured the aircraft; and waited to see what surprises it had in store. When we managed to get the flaps past five (a small victory worth celebrating); we figured; 'Hey; let's just ease our way in and keep configuring on the way.' So; that's what we did--slow and steady in Alternate Flap Extension Mode like a well-behaved crew.We gave ATC a heads-up about our turtle-like speed and minor flight control drama. But hey; no need for a full-blown emergency; just have the trucks ready at the runway; just in case; you know?Final act: We nailed the landing with flaps 20 and max autobrakes--no drama; no fireworks; just pure; unadulterated competence. Except… the fire trucks? Nowhere to be found. Apparently; our request for a welcoming committee got lost in translation.Moral of the story? Plan for the worst; hope for the best; and never trust that the fire trucks will actually be where they're supposed to be.After Maintenance) looked into the issue; they found a bad sensor on the #9 slatIf we had the presence of mind to remember that we wouldn't get a flap indication until flaps five or beyond; we could have used the flap handle to move the flaps instead of motoring them down in alternate mode. We just went to flaps one and didn't see the needle move and moved on with the thought we needed to go to Alternate Mode.
Second reporter narrative
After takeoff and selecting the flaps from one to zero; we were presented with an LE SLAT ASYM indication. We continued the flight and elected to stop at flight level 180; keeping the speed below 250 knots. The FO pulled out the Non-Normal Checklist; and we complied.At this time; we were over the water and using airplane-to-airplane communication relay as we were out of VHF communication range. We were also in contact with the company. We had 60;000 pounds of fuel.After discussing the situation with the company; we elected to return to ZZZZ. Due to uncertainty regarding the aircraft's landing configuration; we decided to pull out the landing configuration charts and calculate performance for all potential flap settings we might encounter upon landing. Once we had those figures; we proceeded toward the airport.We were also uncertain whether a no-flap landing at ZZZZ was feasible due to the high elevation. We decided to continue toward the airport and configure the aircraft as we got closer. Once we confirmed we could extend the flaps past five; we elected to continue with the long arrival and configure while on the approach. We were in Alternate Flap Extension Mode.We advised ATC of our slower-than-normal airspeed and our flight control issue. However; we did not declare an emergency--only requested that emergency vehicles be positioned at the end of the runway as a precaution.We landed with flaps 20 and max autobrakes without incident. However; the fire trucks were not at the end of the runway when we landed.After Maintenance looked at the aircraft they found a sensor issue on the number 9 slat.In retrospect we could have used the flap lever; instead of the alternate flap during the checklist since the flap position indicator may not move until flaps 5 or greater is selected.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.