Originally Posted by
NorthFlyer
But I think you still need to be careful about which FF number you input into your reservation record. Somebody please correct me if I am wrong, but it is my undertsanding that if you fly Aer Lingus Express on a UA code-share, you wil not get credit if you use your CO OnePass account number, but you will get credit if you use your UA MileagePlus number.
Yes, that's correct. CO doesn't have a codeshare agreement with Aer Lingus.
You should always pay attention to codeshares and alliance flights, even when it's not specifically a codeshare. For example, you can credit a LH flight to either CO or UA, regardless of how you booked it, but you'll get different results. For example, you can credit a LH "T" fare (when it's a EU flight connecting to a transcon) to UA but you'll get no miles with CO. Conversely, a LH "P" fare will earn more EQM with CO than with UA.