Narrative:

I was captain (pilot flying) during the autopilot climbout; everything was normal until we leveled off at FL250. The transponder altitude reporting was set to the left position. We then received an EICAS message altitude disagree. We quickly scanned the flight instruments and saw that the first officer's barometric altimeter was reading 280 feet higher than my barometric altimeter that read FL250 exactly. The standby altimeter read 580 feet higher than my barometric altimeter. I told the center that we had an altimetry problem and asked him what he read out on his altitude readout. The center responded FL250. We asked to stay below the rvsm airspace and were assigned FL270. The first officer pulled the procedure out for the irregular procedure and we followed SOP. I gave the airplane and radios to the first officer and used ACARS to contact dispatch and maintenance and explained what happened. I needed fuel burn for FL270 at mach .76 or 300 knots and dispatch had given me a burn of 2;500 pounds more than we had on board based upon mach .78. I asked if we could divert into a nearby airport for fuel and dispatch told me that airport was an emergency airport only for the 767. There were no other viable alternates beyond that airport. That is not comforting in a 767. I sent a position fix report and at that point we had a fuel load of 22.4. The first officer pulled out his flight manual and determined that the nam per 1000 pounds of fuel was 44/1000 at FL270. He also showed me the 300 knot cruise data and determined the landing weight; reviewed the diversion checklist with me and several other critical bits of information to assist me make the best decision for us. Our fuel flow was at 11;000 pph. We estimated the time to the next downline airport was 1 hour 32 minutes which would have put us on the ground with 6.0 in a B-767. The weather was VFR; however; there was no room for error. Dispatch tried to get special clearance from ATC to enter rvsm airspace; but was unsuccessful. After discussing the situation with the first officer and dispatch; I felt it the safest decision to return to departure airport. All of these things happened at the critical time for a decision to be made; as our fuel was critical. We got a clearance from ATC and a right turn for the arrival into our departure airport. I told ATC that we had to return because we could not climb higher into rvsm airspace and that our fuel would not allow us to continue. I discussed with the first officer my concerns that I really did not know which altimeter was lying to us; and that we could have a 280-foot error on arrival; so I wanted to declare an emergency with ATC (which we declared); with conditions. Those conditions were that: we receive no priority handling and that we have no equipment waiting upon arrival. We sent dispatch a message reflecting the declaration. The remainder of the flight was normal. Emergency equipment was waiting upon arrival after we asked center and approach not to have them waiting. We told tower that we did not need their services. This would be a great training scenario because there were many issues/distractions and the fuel condition was critical when the problem took place.

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Original NASA ASRS Text

Title: A B767-300 flight crew received an EICAS message alerting them to an altimeter disagreement. They declared an emergency and returned to departure airport.

Narrative: I was Captain (pilot flying) during the autopilot climbout; everything was normal until we leveled off at FL250. The transponder altitude reporting was set to the left position. We then received an EICAS message ALT DISAGREE. We quickly scanned the flight instruments and saw that the First Officer's barometric altimeter was reading 280 feet higher than my barometric altimeter that read FL250 exactly. The standby altimeter read 580 feet higher than my barometric altimeter. I told the Center that we had an altimetry problem and asked him what he read out on his altitude readout. The Center responded FL250. We asked to stay below the RVSM airspace and were assigned FL270. The First Officer pulled the procedure out for the irregular procedure and we followed SOP. I gave the airplane and radios to the First Officer and used ACARS to contact Dispatch and Maintenance and explained what happened. I needed fuel burn for FL270 at mach .76 or 300 knots and Dispatch had given me a burn of 2;500 pounds more than we had on board based upon mach .78. I asked if we could divert into a nearby airport for fuel and Dispatch told me that airport was an Emergency Airport only for the 767. There were no other viable alternates beyond that airport. That is not comforting in a 767. I sent a position fix report and at that point we had a fuel load of 22.4. The First Officer pulled out his Flight Manual and determined that the NAM per 1000 pounds of fuel was 44/1000 at FL270. He also showed me the 300 knot cruise data and determined the landing weight; reviewed the diversion checklist with me and several other critical bits of information to assist me make the best decision for us. Our fuel flow was at 11;000 PPH. We estimated the time to the next downline airport was 1 hour 32 minutes which would have put us on the ground with 6.0 in a B-767. The weather was VFR; however; there was no room for error. Dispatch tried to get special clearance from ATC to enter RVSM Airspace; but was unsuccessful. After discussing the situation with the First Officer and Dispatch; I felt it the safest decision to return to departure airport. All of these things happened at the critical time for a decision to be made; as our fuel was critical. We got a clearance from ATC and a right turn for the Arrival into our departure airport. I told ATC that we had to return because we could not climb higher into RVSM Airspace and that our fuel would not allow us to continue. I discussed with the First Officer my concerns that I really did not know which Altimeter was lying to us; and that we could have a 280-foot error on arrival; so I wanted to declare an emergency with ATC (which we declared); with conditions. Those conditions were that: we receive no priority handling and that we have no equipment waiting upon arrival. We sent Dispatch a message reflecting the declaration. The remainder of the flight was normal. Emergency equipment was waiting upon arrival after we asked Center and Approach not to have them waiting. We told Tower that we did not need their services. This would be a great training scenario because there were many issues/distractions and the fuel condition was critical when the problem took place.

Data retrieved from NASA's ASRS site as of April 2012 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.