Saturday, June 07, 2008

Feet Wet

After being thwarted the day before, we resolved to launch at 6am and get out over the Bahamas before the sun started the atmosphere boiling again. The forecast called for thunderstorm cells to remain active just off the east coast of Florida, but hope springs eternal and I went to bed an optimist.

Before turning in, I needed to prepare an ICAO flight plan, something I've actually never done before. One of the reasons is that AOPA successfully lobbied the FAA to not implement them and to keep the old, U.S.-style flight plan forms. Sometimes I wonder about AOPA, especially since ICAO flight plan forms will soon be required if you plan to file RNAV-direct.

Lucky for us, there's DUAT and DUATS, which both provide an HTML-based ICAO flight plan that's pretty easy to use. I'm a bigger fan of DUAT that DUATS, mostly because DUATS seems like it was designed by nerdy, programmer types. Having to enter altitudes in a certain way, having some time formats being incompatible with certain output formats makes me feel like I'm beta-testing another programmer's code. These are things that grate on my nerves, but in fact DUATS would turn out to be more useful for filing ICAO flight plans that DUAT.

My approach with DUAT was to create a flight planner with the desired route. When I can get the DUAT flight planner to accept the route, I've always been able to file an IFR flight plan using the same route. One small problem, DUAT doesn't provide winds aloft data for the Bahamas and Caribbean. In fact, I can't really find anyone who provides winds aloft forecasts for this area. Spotty or non-existent surface observations, incomplete or poorly formatted terminal forecasts, and no NEXRAD weather radar images would turn out to be a recurring theme on the last few legs of our trip.

We were up at 4:30am with the intention of being out of the hotel by 5am and loading the plane by 5:15am. I went to DUAT to file two ICAO flight plans for my next two legs, but the first one came back with an error in the route. The cryptic message said I had to use DCT between segments. "Which segments!" I screamed. I fooled around, but couldn't get it to take anything. So I resurrected DUATS. Cursing and swearing my way through, I actually got both flight plans filed and we got out of the hotel a bit later than planned.

The sky was still dark and frequent cloud-to-cloud lightening was clearly visible to the east, exactly where we'd be heading. With the plane preflighted and loaded, I called for my clearance and was told there was a problem with my flight plan and we had to wait while Miami Center fixed it. The controller called back with my clearance and no sooner had I written it down and read it back, the controller said to wait because Miami Center was changing it again. This happen three more times before I was given my final clearance. A quick glance at the 496's Nexrad images made me think that Miami Center was trying to concoct a plan in advance to keep us out of the convective activity and to be honest, the plan looked pretty good.

Once we were airborne, there was a constant stream of requests from every aircraft aloft to deviate this way or that. And we were one of them. With the aid of the 496, we ultimately decided to deviate 30 miles to the north to get around the action rather than risk trying to penetrate the line using Nexrad. The ultimate combo would of course be on-board radar and Nexrad.

Ultimately our early-to-rise strategy worked. We got around the worst build-ups east of Miami and only had to dodge a few clouds with vertical development up to 14,000 feet or so. This was pretty easy because we were in the clear and they were easy to see. A ten degree turn left or right was usually all that was required. These build-ups were often smack in the middle of our route because we were headed to VOR or NDB on an island. If you ever get lost while in the Bahamas or the Carribean, just heard for a towering cloud because it's probably right over a land mass.

This was a long leg - around three hours and forty-five minutes. Without a winds aloft forecast, I was closely watching our ground speed and using the Garmin 530's Density Altitude and Winds Aloft feature to monitor winds aloft. We had an 8 knot headwind component which was not a problem. Anything more than a 20 knot headwind would have meant we'd have to land earlier than our planned destination or get below the minimum 1.25 hour fuel reserve requirement I'd set for myself.

An hour past Stella Maris, we began to hear smaller aircraft asking to deviate around build-ups in that area. It had been relatively clear when we'd passed through, mainly due to a high cloud shield that was preventing the sun for reaching the ocean and working its usual mischief, but those high clouds had now dispersed. I never found out for certain, but I suspect the high level clouds might have been some leftover moisture from the recent tropical storm over the Yucatan.

After three hours and 10 minutes, Miami Center handed us off to Provo Approach and we began our descent to Providenciales. This is where the controllers started sounding a bit different and the flight procedures began to be new for me. The transition altitude for Provo is 6000 feet so you refer to an altitude of 6000 feet or higher as a flight level; 9000 feet becomes flight level 090. You set your altimeter to QFE when you are flying at or above the transition altitude. Below the transition altitude, you set QNH in the Kollsman window, which should correct the altimeter for local atmospheric pressure and show your height above sea level (not corrected for temperature). Below the transition altitude is also when you start referring to your altitudes in thousands and hundreds of feet. At least altimeter settings were still in inches of mercury. That wouldn't be the case later.

I had to consciously remember to include November in our tail number and to refer to altitudes above 6000 feet as flight levels. If you are IFR, the controllers ask you to estimate when you will cross a FIR (flight information region) boundary fix. This is like the ADIZ (air defense identification zone) that surrounds the U.S., but quite a bit less paranoid. If you have a FIR fix programmed into your GPS, estimating you time to that fix is easy. The controllers also want you to fly an approach if you are IFR, even if you are in visual condition. I suspect that many of the approach control facilities have no radar and flying an approach provides them a way to know your position and to provide separation with other aircraft.

They may also ask you to report your distance from a fix when it isn't easy to do it. I had to put the 530 into Etch-a-Sketch mode at one point to tell them my distance from the Intermediate Approach Fix because my 530 was only telling me my distance to the Initial Approach Fix, which was the current waypoint. Below is a photo of base to final at Providenciales.

The staff at Provo Air Center were great. They helped us clear customs, which was a polite and low-key event, then helped us find a bite to eat while they refueled the plane. When we returned, they checked with Provo Approach to ensure our flight plan for the next leg was available. It wasn't. Somehow DUATS or Miami Center lost it, but the Provo staff faxed my paper version and soon we were motoring past Grand Turk Island on our way to Aguadilla, Puerto Rico.

But our thunderstorm dodging wasn't done yet and the XM weather display on the 496 quit working after Provo. Prior to reaching Provo, we had scrolled ahead to look at the Nexrad images for Puerto Rico. Now all we saw was "No XM Signal." Bummer!


crazyscot said...

Great write-up. One thing I can't agree with, though. QFE is not a setting of 1013; it's the altimeter setting which reads zero height on the airfield. (I don't think 1013.2 has a Q-code. The nearest thing I've heard is the rare QNE, which is what your altimeter reads on the ground when set to 1013.2 .)

Almost the entire world has long since ditched the idea of QFE, save for the UK; it works for us here because most of our airfields are not all that far above mean sea level. When making an approach, we're normally given the QFE setting; we're taught to fly around on QNH / 1013.2 depending on altitude (and our TA is quite low; varies from 3000' to 6000' across the country). It's quite common for the circuit height to be described as 1000' on QFE. (But, conversely, I'm learning the gauges right now, and am being taught to fly approaches on QNH.)

John said...


Thanks for the correction.

The thing that fascinates me is that QFE and QNH rarely differ in the Caribbean (at least in my limited experience) by more that a millibar or so. That's seems like a lot of trouble for 29 feet.

As for the transition levels, the fact that some Caribbean TCAs use 4000 and some 6000 feet seem incredibly arbitrary, tedious, and pointless. It only serves to increase a pilot's or flight crew's workload and creates potential confusion. I don't see it doing anything to actually enhance safety.

Maybe I'm just used to the U.S. system, but it seems much simpler (and safer) to have ATC tell everyone an altimeter to use when approaching a terminal area for the purposes of landing or transitioning through. If you're beginning an approach to a particular airport, use the altimeter reading for that airport.

But hey, that's just me ...