March 2005
I flew from my home base (Modesto, Calif.) to Santa Monica this past weekend, and encountered a situation I’d never quite run into before: trouble coming up with a workable IFR alternate.
An alternate is a place to land in case you can’t get into your intended destination. It’s required on IFR flights, unless the destination weather follows the 1-2-3 rule: For one hour before and one hour after your planned time of arrival, you must have a cloud ceiling no lower than 2000 MSL, and at least 3 miles visibility.
Practically speaking, that means your destination is VFR, and expected to stay that way. If the weather’s not that good—and when I was planning these flights, it wasn’t—then you must declare an alternate.
You can declare any airport, whether or not it has an instrument approach, as an alternate if the forecast weather will allow you to operate VFR from the MEA on your route all the way through approach and landing.
That may work, if you can find a location within range that has VFR weather. Or you can use most—but not all—airports that have an instrument approach. In that case, the weather must be forecast to meet alternate minimums, which are higher than regular minimums.
Standard alternate minimums are 600 MSL and 2 miles for precision approaches, or 800 MSL and 2 miles for non-precision approaches, but this can vary from airport to airport depending on terrain and other considerations. The idea is that if you’ve already flown to your primary airport and couldn’t get in, the alternate should be a place where you have a better chance of making a successful approach.
Before filing an instrument alternate, it’s a good idea to pull the approach plate and check—because there are some instrument approaches that are Not Authorized (N/A) for use as an alternate. This currently includes most GPS approaches, although that’s beginning to change as WAAS rolls out (see AIM 1-1-20).
In other cases, there may be limitations on when you can use an airport as an alternate—at Santa Monica (SMO) this is restricted to hours when the tower is operating.
Where do you look for alternate minimums? In NOS chart volumes, there’s a section listing alternate minimums for all airports in the volume. Jeppesen does things a bit differently, listing alternate minimums on the airport diagram in a section labeled “for filing as an alternate.”
If you don’t see that section, then standard alternate minimums apply. Even if the plates indicate that an airport may be used as an IFR alternate, and the forecast meets alternate minimums, you may not be able to use it if the VOR, NDB or other NavAid used for the alternate approach is unmonitored, or if the ATIS/ASOS is out of service.
While technically not required, it’s a good idea to designate an alternate when filing to an airport in the mountains, even if the forecast weather exceeds the 1-2-3 rule. AIM 5-1-8(b) covers three such situations: First, there are three US airports where all approaches have minimums higher than 2000 MSL and 3 miles. Not surprisingly, two of them (South Lake Tahoe and Bishop) are in California—the third is Aspen, CO.
Second, there are what the AIM identifies as “a small number of airports” where the MDA is just barely higher than 2000 feet. Third, at many airports, the lowest MDA listed on the approach may require additional equipment (usually DME, sometimes a RADAR fix) that may not always be available.
My personal approach to this has been to find an alternate that’s VFR and forecast to stay that way. That avoids the risk that an airport that was forecast to meet alternate minimums when you took off turns out to be a whole lot worse when you get there. This usually works—if we’re socked in here in the Valley, it’s usually clear on the coast, or in the foothills of the Sierra Nevadas.
On trips to Southern California, you can usually expect weather that socks in the LA basin usually not to affect airports in the desert, and vice versa. Now that I’ve set the stage, let me tell you about this weekend.
We’ve been planning the trip for awhile, so I’ve been watching “Weekly Planner” on The Weather Channel. The monsoon rains that clobbered both central and southern California a week or two ago are long gone—the “trough” in the jet stream that drove them has turned into a “ridge” with high pressure over the Sierra Nevada mountains. As a result, we’ve had a stable air mass over the area for more than a week… and gray skies that whole time.
When I checked weather the night before the flight, I was told to expect IFR here at Modesto for my departure, due to widespread fog. Once I got on top of the fog, though, I should have pretty much VFR-on-top all the way to Southern California and—wonder of wonders—VFR for my arrival at Santa Monica.
Pleased with the thought of getting out of the valley and seeing some sun, I went to bed. Checking weather again the next morning, it was IFR here, as expected… and also IFR at Santa Monica! Santa Monica’s only instrument approach is a VOR or GPS-A with fairly high minimums: 680 MSL and 1 mile with a radar fix, a bit higher without. Current conditions at Santa Monica were below that, though forecast to increase.
On the other hand, Van Nuys (which is in the foothills a few miles north of SMO) was above the fog, reporting 9 miles and clear below 12,000. So I declared it as my alternate, took off, and figured I’d check in with Flight Watch on the way down. If SMO cleared to at least the required minimums, I’d land there, and if not I’d go to Van Nuys.
As it turned out, when I called (about one hour out) Santa Monica was VFR—barely. It was reporting 3 miles in haze, clear below 12,000. So I stuck to my original flight plan. ATC cleared me to intercept the VOR-A final approach course, cleared me for the approach and told me to contact the tower. I did, and the tower controller proceeded to clear me for the visual approach.
That surprised me—the haze was pretty thick. I repeated back “cleared visual approach” but decided to keep flying the VOR approach. Good thing, as I didn’t see the runway until I was 2 miles out!
The next morning, I called in to check weather for my flight home, and found basically the same conditions—Santa Monica, which would now be my departure airport, was barely VFR. The entire valley, including Modesto, was socked in with fog. Modesto was above minimums for the ILS-28R approach, but not by very much: 300 feet and 3/4 of a mile.
Clearly, an alternate was called for. That proved to be a problem—because the fog was really widespread. Usually, you can use an alternate to the west like Livermore, but it had fog too. Or you can use an airport in the foothills; but this time even South Lake Tahoe and Reno were socked in!
I got on DUATS, and requested an area forecast, looking for any airport reporting VFR conditions within 50 miles of Modesto. Not one—all were reporting IFR conditions, and most were low enough that I didn’t bother looking at alternate minimums. I was beginning to wonder if we’d have to rent a car and drive home!
One last time, I ran a DUATS area forecast—this time expanding to 100 miles. Two airports popped out: Auburn, in the foothills about 70 miles northeast of Modesto was clear, and so was Oakland, about 40 miles west. Both were forecast to remain clear.
I filed for Oakland as my alternate. The actual flight was just as you’d expect—hazy VFR out of Santa Monica, then VFR on top of a widespread overcast as we proceeded up the valley. ATC had me start descending about half an hour out, and vectored me to the ILS localizer well outside the marker.
We were in the soup for about 2 minutes and had the runway about a mile out (the fog was lifting a bit by the time we got in). Landing was no problem.
John D. Ruley is an instrument-rated private pilot, and a freelance writer specializing in science and technology. He’s also a volunteer pilot for LIGA International (www.ligainternational.org), and past president of the Modesto Airport Pilot’s Association. You can write to John at jruley@ainet.com.
