Date: 201504
Local time of day: 0601-1200
Location: ZAU.ARTCC, IL
Flight conditions: VMC
Aircraft: EMB ERJ 190/195 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZAU
ATC / advisory: Center ZAU
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification
Second reporter function: Pilot Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Dispatch
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Manuals
Primary problem: Human Factors

Narrative: I was aware of the ozone limitation but I found out that I have been mis-interpreting the charts. This was an empty repo leg without any passengers.  We were filed low at FL310 but we were empty and I thought it would be good to save some gas by climbing higher.  I looked at our position sensors and saw that we were about N40'19; W87'51.  I looked at the ozone charts in the SOP.  For April at 40'N the chart says FL382 max.  However I had always thought that the E and W pertained to what hemisphere you were located in.  I discussed this with my First Officer (FO) and we both thought the same thing.  So I requested FL370 from ATC.  We climbed up and reaching FL370 I send my dispatcher an ACARS to amend the release to show FL370 as our new altitude.About 15 minutes later my dispatcher sent us an ACARS saying that they max ozone altitude was FL366 and that we needed to descend.  He informed us that the note about the reference line of 100'W is the divider between East and West.  We descended to FL360 and the rest of the flight was normal.  The only memo I found about the ozone table was from 2013 stating that we must use it.  I have always referenced the SOP ozone table but I believe that the guidance on how to use it is kind of vague.  I have been mis-understanding how the East and West columns were determined.  It makes since now that someone explained it to me.  I believe that there is a general consensus that the E and W are the hemispheres.  That is how I learned it while an FO; so I always just assumed it to be true.


Second narrative: We were originally filed for FL300 on the flight. We were a repositioning flight and ride conditions were good so we checked our ozone limitation tables; agreed we were to use the west numbers and determined we could climb to 370 and save some fuel. We were cruising at 370 when our dispatcher alerted us to the ozone limitation of 360. We rechecked our tables and queried him about which numbers he was using. After discussion between the Captain; myself; and our dispatcher we were enlightened that we were east of the 100 west line so we were to use east numbers. We descended to FL 360 and completed the flight. Better education on exactly what separates the east from the west numbers.


Synopsis: An EMB190 Captain discovers that he has been misinterpreting the ozone tables provided by his company; in that the east and west charts refer to east and west of 100°W and not the hemispheres.