These are the steps:
1 go to: http://www13.lanchile.com/espanol/un...s/indexNew.htm.

2. enter your ff number and password
3. in the following page choose the first option
4. in the next page write MADRID in the slot for "Origen" and Mexico City for "Destino" (it does not accept city codes like MAD or MEX). Choose the dates for outbound and inbound, for example March 20 and 27. Choose your class (economy=turista, ejecutiva=business, Primera=first).
click on "buscar vuelos".
5. in the next page will show any direct flights avaliable for that date (in any OW airline) to your destination, and some indirect flights. Click on "Verificar disponibilidad y kilometros requeridos". If you get a red spot in the flight selected, it means there is no space avaliable, choose a different flight or move to a different date until you get confirmation.
6. If the spot is available for a Lan award, it will be availiable for any other OW partner.