If you are trying to qualify for British Airways Executive Club Bronze, Silver or Gold then you will need to have ‘Eligible Flights' in addition to Tier Points. You need as follows:

• Bronze – 2 Eligible Flights
• Silver – 4 Eligible Flights
• Gold – 4 Eligible Flights

These are not cumulative. If you want to go from zero to Gold in a single year, for instance via a Tier Point Run, you only need 4 Eligible Flights.

What is an Eligible Flight?

In layperson's text, there are only three possible scenarios for an ‘Eligible Flight', all of which must come from cash-purchased tickets and not from an Avios redemption:

1. If you fly in a British Airways branded plane
2. If British Airways sold you the ticket AND it has a BA flight number.
3. If Iberia sold you a ticket AND it is flown in an Iberia branded plane.

That's it.

You can also verify this by looking in Manage My Booking and checking your Fare Class.

I have quoted the relevant part of the official terms and conditions below, which is basically a longer-winded of what is mentioned above:

Eligible flights are defined as those flights marketed or operated by British Airways and those flights marketed and operated by Iberia.

• ‘Marketed' means the flight will have a BA flight number (in your itinerary or on your ticket).
• ‘Operated' means the aircraft that you travel on is a British Airways aircraft (including franchises and BACityflyer).
• ‘Marketed and operated by Iberia' means the flight will have an IB flight number and the aircraft you travel on is an Iberia aircraft (including franchises).

Reward bookings and agency or industry discounted bookings are not eligible.

The official text of British Airways Executive Club can be found here, if you want to read the full text.