Direct RNAV routing in Mexican Airspace?

[Garrik66]

Working on a route for a flight from Brownsville, TX to San Jose, Costa Rica.

The best route would require long direct legs, because there are no airways that go in that direction.

But an acceptable route would require one relatively short direct leg, from RADAS just off the coast near Matamoros to LIRPO, where I can pick up UM206. That direct leg would be 157 off airway miles.

Anyone have any sense whether I am like to get that routing if I ask for it, or if they will force me onto an airway immediately?

Also, can anyone verify that there is VHF coverage over the Gulf along e.g. UM206. I assume that there is.

Thanks much.

[Garrik66]

Ok, now that I have flown the outbound leg, I know the answer to my own question :ok:

I departed Brownsville (KBRO) and was given a direct climb to FL410 (this is in an M2) and handed off to Mexican departure control. I made my request (for direct LIRPO and UM206, instead of flying UT22 to UL207), and got back "let me check with Center." The controller spoke perfect English. He handed me off to Monterrey Center, and a few minutes later I was cleared direct present position to Campeche (CPE), which is the VOR on the Yucatan coast at the other end of my airway route over the gulf. I was in radar and VHR radio contact with either Monterrey Center or Merida Center (the Yucatan Center) for essentially the entire route (except for maybe 10 minutes in the middle of the gulf, when Monterrey handed me off and I could not yet quite copy Merida).

I got there (to CPE), resumed my airway route for maybe 120 miles, and then somewhere shortly before the Belize boarder (also the FIR boarder) was handed off to CenAmer Control (the unified center that owns the high (>FL200) airspace over Central America). In his first transmission, the CenAmer controller (who also spoke perfect English) cleared me direct Liberia (LIB) and the arrival into San Jose. Again, I was in radar contact for the entire route.

I had a chance to ask CenAmer if I could file a direct routing to start with. He said "no", that I needed to file a complete airway route, but that I could ask for direct routing once in their airspace. And based on what I heard given to other aircraft in their airspace, a direct climb to the filed cruise altitude and RNAV direct routing (to an RNAV fix at the FIR boarder) appears to be the norm for any appropriately equipped aircraft.

This entire experience was quite different than what I have dealt with in western Mexico or the Caribbean in the past, where radar contact is spotty or non-existent, and direct routing not available except from American controllers.

So the short answer to my question is that radar coverage and VHF radio coverage is to be expected over this route, including the portion over the gulf, and that assuming no conflict with other traffic, RNAV direct routing within FIR boundaries is not only possible, but likely.

If I get something different on the way home, I will report back - otherwise, I leave this in the hopes that it will be useful to someone in the future.