B767-300 and 300 ER
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action
Aircraft
After completing my assignments as observer pilot; I proceeded into the crew rest area. I was awakened by a FA (Flight Attendant) several hours into our planned 8 hour flight; and was told the CA (Captain) requested my presence in the flight deck. Upon arrival into the flight deck; I was informed about a situation with the left engine oil quantity. The crew had noticed the left engine oil quantity had diminished to 12 quarts from a pre-departure quantity of 22 qts. The right engine showed 17 qts; also from a 22 qt pre-departure quantity. We continued to monitor and time the quantity loss for the left engine and determined we were indicating the loss of oil at the rate of 1 quart every 29 minutes. Left engine oil temperature and pressure parameters were normal. We called our in-flight mechanic up to the cockpit for further evaluation. His recommendation was for a turn back. We SATCOM called dispatch then conferenced in maintenance control as well as the Director of Operations for further evaluation. During the course of the conference call maintenance control and the Director of Operations both felt it was most likely an indication problem but stated that it was up to our Captain. Our Captain discussed it with us and we came to the decision; as a crew; to divert. When the left engine oil quantity was 10 quarts we determined our best course of action was to divert. After receiving clearance from ATC we then proceeded toward [the diversion airport]. We later received an ACARS message from company requesting we proceed to [a second diversion airport] for better handling. A live recalculation was completed for the new airport. We conveyed this information to ATC who then cleared us to [the new diversion airport].
Subsequent ground maintenance inspection located a faulty canon plug and wire connector that duplicated the rapid loss of indicated oil quantity we were seeing in the cockpit. The left engine had full oil quantity when we landed.I could increase the frequency of scanning the engine instruments to next time act sooner. Crews should be made aware of the .25 qts per hour oil consumption rate allowance for ETOPS flights. We were unaware of this until our flight mechanic mentioned it.
B767-300 flight crew reported a steady loss of indicated oil quantity on their left engine several hours into an eight hour flight and determined that the oil would be depleted before reaching destination. The crew elected to divert to a suitable airport. Maintenance discovered a faulty cannon plug that replicated the decreasing quantity while the oil tank was full.