I was getting set-up to practice my ILS approaches and landings and decided to try one at a scenic location, Princess Juliana (TNCN)and was surprised to find that Princess Juliana has no ILS at their airport. I then started wondering what's the criteria for obtaining an ILS at an airport? Cost would be a factor, but is their anything else?

Sure there is. Terrain is probably the main factor and proximity to another airport. Here in Las Vegas I fly out of Henderson Executive quite frequently, both for real and in the sim. The management at Henderson tell me that they are not able to have an ILS to the south due to low terrain (mountains) and to the north because of KLAS (McCarren Int.). I guess that a glideslope cannot exceed a certain approach degree, or can't be too steep, not to mention that you can't have two ILS glidelopes intercepting each other in the air from separate airports. KLAS's glidslopes for RWY's 25 L & R are just too close to KHND to the North. Cost isn't a factor there, It's the FAA. lol.

Thanks for the response, guess it's cost then at Princess Juliana; no FAA or terrain difficulties for runway 09 at that location.

There are a couple reasons for no ILS at TNCM - the main one is that the cost of building, maintaining and running an ILS is not justifiable for the necessary usage.An ILS is for IMC. That is the main criteria - the need to facilitate landings in Instrument Meterological Conditions.To my knowledge six airports in the Caribbean fulfill any need for full IMC landings for all the other airports in the region - TJSJ, TISX, TIST, TFFR, TFFF, TBPB.TNCM has a perfectly acceptable, perfectly workable VOR Instrument Approach, but the basic fact is that 350-360 days a year, visual landings at TNCM are not obstructed by weather.I lived four years on Antigua and the only days I remember TAPA or TNCM and the other airports not open and available for landing due to weather was when hurricanes closed the airports.Yes, sometimes aircraft do have to divert to an alternate - the AFR Concorde landed on Antigua one day. TAPA, TFFR and TISX are all good alternates to TNCM and two have an ILS.If a pilot is not capable, comfortable, experienced and current at landing a MD-11, B747 or A340 visually - he should not be flying that aircraft in the real world.One flight I was on was scheduled to land at TNCM before landing at TAPA, but we overflew TNCM due to not having a parking space available for the AAL B727. The airline put the TNCM passengers in a hotel overnight and dropped them at TNCM on the outbound flight the next morning.There are about 100 major commercial airports I've found around the world with no ILS. About 50% of those are like PAJN where terrain makes an ILS approach impossible. The other 50% tend to be in the tropical regions where weather conditions and nearby alternates make an ILS a questionable financial choice.