Narrative:

Just after push back we had to crew defer the right eec system; which also prohibited us from using the auto-throttle system. Other than that; we had a somewhat routine departure; climb; and cruise. As we left our cruising altitude to begin our descent for landing; I believe that we were VMC. I was flying; but the captain turned on the wing and engine anti-ice himself in anticipation of the moisture below. Somewhere shortly after we started down; we were IMC and remained this way for most of the remainder of the flight. Approaching FL240; we got a rudder ratio EICAS message; and the captain's airspeed went down to around 140 knots. Next; we got an autopilot EICAS message; and I immediately turned off the autopilot and hand flew it for the remainder of the flight. Maybe a minute later the airspeed on my side became unreliable as well. We declared an emergency and accomplished the non-normal checklist. We requested to get vectors to VMC conditions; but there weren't really any large areas of VMC in the area. The captain asked for the current weather at [the three nearest airports]. The weather at destination was marginal and we were seeing flashes of lightning in that direction. We discussed our options; and both thought that ZZZ was the best place to land. The captain requested constant altitude and groundspeed readouts from ATC. From FL240 to about 14;000 feet; this was the only airspeed I trusted. At about 14;000 feet it seemed like the standby indicator was beginning to give readings that were consistent with ATC's groundspeed callouts. Shortly after that; my airspeed indicator became intermittent. It would temporarily match the standby indicator then go much slower; and then go away completely. Going through about 5;000 feet my airspeed remained consistent for the remainder of the flight. I was too focused on hand flying the approach; and keeping my speed to remember what happened to the captain's airspeed indicator. We got vectors for a long (10-15 mile) straight in ILS and landed with no further incident.this summary is pretty straight forward; but this was an extremely stressful event. The combination of flying IMC; at night; with no reliable airspeed indicator; no auto-throttles; and being in an aircraft with fuel flow in kilograms; while relying on a procedure that says 'maintain pitch and power setting for phase of flight'; made this a very uncomfortable flight. I think the captain and I worked very well together to create the safest outcome. The captain's communication with ATC was instrumental as well.

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Original NASA ASRS Text

Title: B767 flight crew describes a decent and diversion in night IMC with all three airspeed indicators inoperative. All three indicators return to normal during approach.

Narrative: Just after push back we had to crew defer the right EEC system; which also prohibited us from using the auto-throttle system. Other than that; we had a somewhat routine departure; climb; and cruise. As we left our cruising altitude to begin our descent for landing; I believe that we were VMC. I was flying; but the captain turned on the wing and engine anti-ice himself in anticipation of the moisture below. Somewhere shortly after we started down; we were IMC and remained this way for most of the remainder of the flight. Approaching FL240; we got a rudder ratio EICAS message; and the captain's airspeed went down to around 140 knots. Next; we got an autopilot EICAS message; and I immediately turned off the autopilot and hand flew it for the remainder of the flight. Maybe a minute later the airspeed on my side became unreliable as well. We declared an emergency and accomplished the non-normal checklist. We requested to get vectors to VMC conditions; but there weren't really any large areas of VMC in the area. The captain asked for the current weather at [the three nearest airports]. The weather at destination was marginal and we were seeing flashes of lightning in that direction. We discussed our options; and both thought that ZZZ was the best place to land. The captain requested constant altitude and groundspeed readouts from ATC. From FL240 to about 14;000 feet; this was the only airspeed I trusted. At about 14;000 feet it seemed like the standby indicator was beginning to give readings that were consistent with ATC's groundspeed callouts. Shortly after that; my airspeed indicator became intermittent. It would temporarily match the standby indicator then go much slower; and then go away completely. Going through about 5;000 feet my airspeed remained consistent for the remainder of the flight. I was too focused on hand flying the approach; and keeping my speed to remember what happened to the captain's airspeed indicator. We got vectors for a long (10-15 mile) straight in ILS and landed with no further incident.This summary is pretty straight forward; but this was an extremely stressful event. The combination of flying IMC; at night; with no reliable airspeed indicator; no auto-throttles; and being in an aircraft with fuel flow in Kilograms; while relying on a procedure that says 'maintain pitch and power setting for phase of flight'; made this a very uncomfortable flight. I think the captain and I worked very well together to create the safest outcome. The captain's communication with ATC was instrumental as well.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.