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Monday, March 30 2015 14:51

Left Coast Pilot: Personal Minimums and the Fog Season

Written by  John Ruley
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Widespread fog prompts a change of heart about personal minimums on departure.

April 2015-

I have never been a fan of personal minimums—the idea that you should set limits for yourself short of what’s required by the FAA. Particularly for instrument flying, if you aren’t prepared to shoot an approach to minimums as specified on the chart, you shouldn’t file, because you’re going to have to deal with whatever weather develops.
That’s one reason for the “1-2-3” rule about specifying an alternate if the weather isn’t forecast to have at least a 2,000-foot ceiling and three miles visibility for one hour before and after your planned time of arrival.

But I’ve had a change of heart, at least in one respect: I’ve now set personal minimums for visibility and ceiling when departing on an IFR flight. That came about as a result of planning for a flight to Los Angeles with my wife during the fog season.

We were in a relatively wet winter season here in California’s Central Valley, which makes fog common. When there’s no frontal weather, radiation fog is common most mornings and indeed sometimes builds up to persistent tule fog that can cover fairly large areas.

Most of the time, the fog will burn off as the sun comes up, but deep in the winter you get a condition where the fog never completely burns off—it just rises into a low stratus, then settles back on the ground at night.
Periodically, a weather system moves through and disrupts the stable pattern, but between those systems, morning fog is the rule here until spring. It’s just something we learn to live with, and one of the reasons that an instrument rating really helps.


That had been happening the week before we were due for our trip: on Thursday, visibility stayed at one-quarter of a mile with an indefinite ceiling at about 100 feet until about 4:00 p.m.—and even after that, never got better than half a mile. That caused me to do some hard thinking.
For noncommercial flights conducted under Part 91, there are no minimum visibility or ceiling requirements for instrument departures; if you can see to taxi your airplane, you can get a clearance (which may include the highly significant words “at your own risk”) and take off.
I’ve never been fool enough to do that, but up to now, my departure minimums were basically the instrument minimums to get back into the airport. At my home base of Modesto, Calif. (KMOD), that’s one-half mile visibility and a 200-foot ceiling for the ILS approach.

What got me to thinking, though, was that the fog was so widespread. The whole valley was socked in.

I have flown in these conditions before, and usually there are just a couple of minutes in the soup on climbout, and then gorgeous clear air above. No problem at all—provided nothing goes wrong. If something does go wrong, with widespread fog and low ceilings, where can you go?
I did a Google search and found some really interesting discussions connected to old magazine articles on departure minimums. Then I picked up the phone and talked the whole subject over with my good friend and longtime flight instructor Larry Askew.

I finally decided that my personal departure minimums are basically the same as commercial pilots use: at least one mile visibility and a 500-foot ceiling. That’s enough that you’d have a fighting chance to live through an engine failure on takeoff.

Fortunately on our departure day, the weather cooperated and the fog lifted by noon. We had a great ride down with a 20-knot tailwind. I was a little nervous as there were multiple AIRMETs (and even a SIGMET) for severe turbulence mainly over the Sierras, but all we got was a mild mountain wave after we crossed the first big ridge near the Lake Hughes (LHS) VOR.

I had a Stratus ADS-B receiver running, and actually saw a fair amount of traffic from it on my iPad—enough to make me wonder if I may have been seeing the benefit of flying near another airplane equipped with ADS-B Out.

I took a few screen grabs, and after looking at those, it was clear we were following a PC-12. Since the tail number showed up, I’m betting the pilot was running an ADS-B compatible Mode S transponder, so ground stations were relaying transponder traffic to him, and while nearby we were picking it up.

That illustrates why you need installed ADS-B Out equipment (a 1090 MHz Mode S transponder or 978 MHz UAT) to get reliable ADS-B traffic. With just the receiver, you sometimes see traffic and sometimes don’t.

I also noticed a few scattered areas of light precipitation—evidently the fog or mist was dense enough to show up on ground-based radar, which is relayed by ADS-B ground stations along with traffic.

The only problem with the flight was that we’d gotten out about half an hour late, so we arrived just at dusk—which put the sun in my face on our long straight-in approach to Hawthorne (KHHR) Runway 25. I was almost blinded and got on the gauges, telling Kate to look for traffic.

Fortunately the sun went down when I was still joining the localizer, which let me flare without squinting.
One odd thing: the final approach controller announced, “Cleared into Class B airspace via the Hawthorne 25 localizer; report the airport in sight”—which was ridiculous as I’d been in the Class B airspace for a good 10 minutes at that point.
I replied that I was IFR. He cleared me for the visual approach.

Two days later, I again had to wait for the fog to start lifting before departing for home. I also decided to fly a slightly different route: instead of directly over the mountains into the valley, I planned to fly up the coast, turning inland at Morro Bay.

The MEAs for the route were all 8,000 feet or less, which eliminated any need to use oxygen. The route is also a bit prettier and kept us away from the fog as long as possible.
However, the route that I filed was pretty complex: KHHR HERMO V23 LAX SMO V107 SADDE V299 VTU V25 RZS V12 GVO V27 MQO V113 PRB V113 ROM V113 PXN KMOD 13GPH 8000FT
The routing was complicated enough that I saved it to Notes on the iPad, and hand-wrote it on my clearance pad.
When I called for my clearance, I received this: “Cleared to Modesto via left turn heading 210; radar vectors Ventura [VTU]; then as filed. Climb and maintain 3,000. Expect 8,000 in five minutes…” and the usual departure control and squawk.

ATC’s vectors were pretty close to what I asked for, except that it didn’t hug the coast quite as much, and probably put us four to five miles out over the water, but by that time we were at 6,000 feet, so I was still comfortable.

It was a pretty flight with no turbulence at all, and no more than a 15-knot headwind. Turning inland we could see low stratus and heavy haze filling the valley. Modesto was reporting four miles and clear below 12,000 feet, but I asked for and flew a full ILS and was on the gauges from about 1,500 feet.

I still don’t believe in setting arrival minimums higher than those for the best available instrument approach. If I’m not up to flying a full ILS, I need to get more practice. But taking off into widespread low fog strikes me as an unnecessary risk.

I’ll add that when I’m planning a flight into an area with widespread fog, I pay a lot of attention to the local weather trend and get very serious with my alternate planning. There’s no sense taking off until—and unless—the trend is improving; otherwise you run the risk of being unable to get in, and if that’s a serious risk, then I want an alternate that’s CAVU.
Fortunately, in N4696K we have long-range fuel tanks, so I usually have a lot of good options.

John D. Ruley is an instrument-rated pilot and freelance writer. He holds a master’s degree from the University of North Dakota Space Studies program (space.edu) and is archivist for the Hubble Space Telescope (HST) operational history project. Ruley has been a volunteer pilot with ligainternational.org and angelflight.org, two charities which operate medical missions in northwest Mexico and provide medical patient transport, respectively. Send questions or comments to This email address is being protected from spambots. You need JavaScript enabled to view it..

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