FOQA, pronounced ("FOLK QUAR") gains data from the quick access recorder on board the aircraft. The event associated with deep touchdown or short touchdown is based on timing from crossing the threshold. This position is acquired from various inputs not limited to the following; DME, Altimeter, Radio Altimeter, G/S on an ILS, Ground Speed. An event will be provided for both an ILS and Non ILS approach and Landing. It is worth noting that the Data is not gained from the Visual Approach guidance systems and these are set to provide a varying difference in TCH ranging from at least 73ft down to in some cases 45ft. This is to suit the "Pilot eye Height" of different aircraft and is normally set for the most critical to give sufficient clearance. On an ILS approach the Glide slope will normally be set to give 50' TCH above the on board glide slope antenna. The aircraft's antenna can be positioned on the aircraft to provide the appropriate aircraft height over the threshold. Now FOQA alerts are normally set for between, less than 1000ft to greater than 2000ft, (300m-600m). Point to note is Runway touch down markings do vary between runways. The "Fixed Distance Marking" large white blocks can be set to start at 1000ft or 1500ft depending on various reasons which is another topic. Prior to these markings are the "Touchdown zone markings" these are the thinner white stripes placed either side of the runway centre line. These "Touchdown zone markings" are located 500ft (150m) from the threshold and then 500ft (150m) after that. Now if you can see two sets of these before the large "Fixed Distance Marking" then these are set at 1500ft (400m) if you can only see one set of touchdown markings (thin white lines), before the Large white "Fixed Distance Markings" then these are set at 1000ft (300m). To help stay in the FOQA limit range use a visual aiming point that is going to have MLG contact runway just past 1000ft point. IE insure you know which is the 1000ft point on the runway, as FOQA does dot make allowances for the different markings. Using a visual aiming point will give a fly up indication on the VASI or PAPI in some cases, however remember the visual approach aid is set to provide guidance for differing "Pilot eye Heights" and these can vary by more than 30ft between aircraft.
Cheers Mang.