This has been discussed a number of times over the past months. Since AC added additional fare classes the normal method no longer include the I-class in their returned list. You need a tool such as Expert Flyer which still shows I-class in its list of all fare classes returned in the result set (as it seems to return a larger buffer) or a tool such as KVS with which you use the Gallileo access method to only choose the I-class to be returned but no others in the same result set. I do not believe that any of the web access methods which freely provided this information can do it any longer, however something may have changed recently.
This is what you will see with Expert Flyer:
Code:
Departing SFO on 05/09/08 0:00 for YYZ Flying AC
Flight Stops Depart Arrive Aircraft Frequency Reliability Available Classes
AC 758 0 SFO 05/09/08 6:45 YYZ 05/09/08 14:39 319 T,W,Th,F 93% / 10m J9 C4 Z1 Y9 M9 U9 B9 H9 V9 Q9 L0 A0 S6 R9 K9 N9 G9 P0 E0 T6 I1
AC(UA) 5660 0 SFO 05/09/08 10:45 YYZ 05/09/08 18:54 319 Daily 78% / 33m J0 C0 Z0 Y9 M9 U9 B9 H9 V9 Q9 L9 A0 S0 R9 K9 N9 G9 P9 E0 T0
AC 756 0 SFO 05/09/08 12:30 YYZ 05/09/08 20:20 319 Daily 52% / 29m J9 C1 Z1 Y9 M9 U9 B9 H9 V9 Q6 L4 A4 S0 R9 K9 N9 G6 P4 E4 T0 I1
AC 784 0 SFO 05/09/08 15:05 YYZ 05/09/08 23:05 319 W,F NA / NA J9 C6 Z6 Y9 M9 U9 B9 H9 V9 Q9 L9 A0 S6 R9 K9 N9 G9 P9 E0 T6 I6
etc...
Expert Flyer also just added a new feature for one button search for I/D/W classes on AC .. very nice.