Date: 201409
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Aircraft: B767 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Leading Edge Slat
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Relief Pilot; First Officer; Pilot Not Flying
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Aircraft Equipment Problem Dissipated; Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Climbing out through around 23;000 feet. I was on the service phone with a Flight Attendant (FA) and I heard a caution sound. By the time I looked up it was gone. The captain requested a level off and advised ATC. Her and the First Officer (FO) said that the slats moved while handle was set in UP position as well as EICAS listed an LE SLAT Asymmetry. She directed me to run the QRH and I did. The Captain and the FO coordinated heading back. I continued with the LE SLAT Asymmetry checklist as well as the Fuel Dumping Checklist with the Captain. We dumped gas. I got our landing performance numbers and completed the overweight landing checklist. As a crew we discussed what to do in case of a go around. We also briefed the approach. And completed all checklists. The captain and I had a discussion about landing at Flaps 20 but we decided against it. We landed and stopped on the runway. Directed by the Captain I got on the PA and said 'Remain Seated; Remain Seated'. I completed the Hot Brakes checklist. We waited on runway until the brakes cooled and we got towed to the gate. While we were in the air the captain did speak to the FAs as well I did. I just don't remember the sequence of times.


Second narrative: During climb out thru FL260 to FL310 the aircraft had a sudden pitch change (the nose came up slightly and the left wing began to rise). At the same time. We received LE Flap light; the flap position indicator on the gage began to move from the up and locked position to flap 1. And as suddenly as the flaps extended they retracted back to up. The Captain was flying with the autopilot on during the occurrence.We leveled at FL260. The Captain put the bank selector to 15 degrees bank and gave me the aircraft. I flew and coordinated with ATC. The Captain and First Officer completed numerous checklists; contacted Dispatch; [Maintenance Control]; FAs and the Passengers. We descended to FL200 and slowed to 250 kts. We asked ATC to give us vectors as close as possible to [the airport] in case we suddenly had to land.We coordinated with ATC for fuel dumping. We informed ATC we plan to land on [the long] runway. All checklists were completed; performances were checked. We decided to try the flaps. If they worked we'd land with flap 30. If not; we would do a flap up or partial flap landing if the flaps did something abnormal again. The captain landed the aircraft safely and softly with flaps 30. We informed the FAs and Passengers to remain seated.We were met by fire services. They noticed no abnormalities. We had to remain on the runway for 75 minutes for brake cooling. Approximately 83 minutes after landing we were met by the towing procession. We were then towed to gate followed by fire services. The passengers disembarked. All [maintenance messages] were sent and we spoke with maintenance. Everyone inside and outside the aircraft did a great job helping assure our safe land and a safe operation.


Synopsis: B767 flight crew experiences an uncommanded LE slat extension climbing through FL230. As quickly as the slat extended it retracted; but the crew elected to dump fuel and return to the departure airport for an overweight landing.