Date: 201905
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 135
Flight plan: IFR
Flight phase: Cruise
Aircraft component: Airspeed Indicator
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: About 6 hours into the flight at FL400; at night; after dodging wx through the ITCZ [Inter Tropical Convergence Zone]; the EICAS displayed 'IAS DISAGREE'.  This EICAS message was not accompanied by any change in attitude; immediately noticeable airspeed error or power.  Called for the IAS DISAGREE checklist from the QRH.  The IAS DISAGREE checklist simply informs the pilot that the CA and FO airspeed indicators disagree; and refers you to the Airspeed Unreliable checklist.  The first few items of this checklist would have you disengage the A/P; turn off the A/T; turn off both F/D; and set a flaps up pitch and power of 4 degrees NU / N1 to 75%.  Because the airspeeds were 'reasonably' matched; we chose not to conduct these first few items.  Our A/S indications were:  CA .798M/242K; Stby ---/242K and FO .815/247K; thus a .017M/5K disagreement.  We did go to the QRH Performance Inflight chapter to determine that at our weight and altitude we should see 2.5 degrees NU and N1 at 89.7% (this is exactly what we had without any adjustment required).  Continuing through the checklist; we switched the FO Air Data to ALTN; removing all discrepancies.  We continued to read the checklist to determine how this might potentially effect our arrival and landing.  The pilot on the observer seat also; retrieved the 767 Systems Manual so we could affirm our understanding of the air data and pitot systems affected.At this point; we were currently about 160NM south of Guam (and headed toward it); and as a crew felt confident in the low impact of this degradation and our ability to continue.  However; we did place a SATCOM call to dispatch; to include a 3-way with Maintenance.  We relayed our aircraft state; and intent to continue unless they had any additional input that might direct us not to pass Guam.  They did not.  They agreed continuing seemed prudent and forecast wx at ZZZZ was OK.  We agreed as a crew to handle any necessary adjustments for arrival via the normal recall review [company] procedures.The next couple hours enroute to ZZZZ were uneventful.  Once the field opened at ZZZZ; and we were able to retrieve ATIS (ZZZZ transmits no ATIS prior to 2030Z); we determined that only Cat III arrivals to RW XXR were available.  We reviewed the B767 QRM Cat II/III Auto-land Approach Required Equipment list and determined a Cat III was still possible using the right ADC in ALTN.  (Side note - we did test the RT Air Data back in normal prior to this; with a resultant large airspeed discrepancy and a momentary Over speed EICAS).  We performed the complete Cat II/III Approach Review and brief for the arrival and Cat III landing.(~9+15 hrs into flight) at FL400; the EICAS displayed AUTOTHROT DISC; L ENG EEC MODE and R ENG EEC MODE.  This indication was cleared by cycling and resetting the auto-throttle.At FL400; the EICAS displayed L ENG EEC MODE and R ENG EEC MODE.  We performed the Engine EEC Mode QRH checklist.  The EECs were operated in ALTN for the remainder of flight.  While we were now discussing that a Cat III was no longer prudent; we received the AILERON LOCKOUT message on the EICAS.  We ran the Aileron Lockout QRH checklist.At this point in the flight I looked ahead on our arrival to see that 'ZZZZZ' had a published hold.  I directed the FO to prep the hold at ZZZZZ and retrieve updated ATIS for our alternate ZZZZ1 and directed the Observer to start calculating a Bingo from ZZZZZ to ZZZZ1.  ZZZZ remained Cat III but was improving as the sun came up separating the temp / dew point spread.  Next I directed the FO to prep RTE 2 for our flight to ZZZZ1 as a contingency.The EICAS displayed RUDDER RATIO.  We asked Approach for holding at ZZZZZ.  We performed the QRH for Rudder Ratio.  During this checklist; we checked the status page and determined the left HYD QTY had dropped to .75.  This checklist has a 15K crosswind and no auto-land limitation.  Winds at ZZZZ were almost nil.I made a SATCOM call to dispatch while holding at ZZZZZ.  This was an abbreviated call.  The intent of this call was not so much to receive input; as it was to inform dispatch of our reasonably high likelihood of a divert to ZZZZ1.  At the tail end of this call; the Duty Pilot (who I was unaware was listening) chimed in essentially; '...don't push it; go to ZZZZ1 if you need'....or words to that effect.For the remainder of the flight; the L HYD System quantity fluctuated between .77-.80.  Pressure however remained OK throughout; and we never received any HYD pressure annunciations.  (I honestly did not look at it too many times; but I believe it stayed 2950+; practically normal.)I think we made 3 turns in holding at ZZZZZ; and during the second Approach informed that the RVR on RW XXL had improved to greater than 2000 RVR.  Subsequently we set up for the ILS Y XXL; departed holding and made an uneventful approach and landing.  It was essentially CAVOK when we landed.No obvious suggestions come to mind.Overall; I believe we exercised CRM and operated well as a crew.  We expanded our crew to include Dispatch; Maintenance and the Duty Pilot more than once.  As time allowed we used secondary manuals (B767 Systems) to enhance our understanding.  At least once; we disagreed on exactly which component had failed; but ultimately agreed on the aircraft state and moved forward.  At least once; a crew member expressed his concern about continuing to ZZZZ.  Those concerns were allayed via contingency plans.Late in the flight; I wondered if operating single ADC effected RVSM compliance.  I decided it did not (that we retained 2 independent altimetry systems); and even if it did; I am valued the 3+ hours of fuel saved at FL400 versus descending out of RVSM airspace.In the cumulative; it was a lot to deal with.  But each of the system degradations happened in a sequential fashion and were dealt with in order.  The morning Cat III weather at ZZZZ was the ingredient that ticked the anxiety box upward.  However; ZZZZ1 was CAVOK and was the out we had left ourselves before bingo.




Synopsis: B767 Captain reported numerous aircraft issues they had to deal with over the ocean.