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Alternates made easy: When the weather's bad, choosing an alternate airport can be a tricky balance of time, distance, fuel and minimums. It doesn't have to be so hard.


Flight under instrument flight rules (IFR) is largely procedural. There's little room or tolerance for zany spontaneity so, if you love surprises, look elsewhere. But although we fly by the book, when the plot thickens, we do in fact have options (although they're more like regulatory provisions) for choosing a different ending. Usually, the thickening agent affecting our best-laid plans is weather-related.

Before we can exercise that freedom of choice, however, IFR pilots must fulfill certain obligations. Some of these rules are similar to those for VFR flight, such as how much fuel we should have on board. Some, however, go literally a step beyond, such as the requirement for specifying an alternate destination (as well as hopefully having some rough plan for getting there). The idea of even thinking of an alternate airport may be foreign for some newly anointed VFR pilots, but in the IFR world, it's a well-known commodity. It's nothing other than simply having a Plan B. In Canada, in fact, there is virtually no such thing as flying under instrument flight rules without an alternate airport, period--at least not without special dispensation from the Minister of Transportation. So yes, IFR flight to some extent allows us the chance, at least to some degree, to punch through certain kinds of weather. But there are limits.


At first glance, the Federal Aviation Regulations covering the choice and specification of alternative destinations can seem convoluted and hard to remember. Actually, it's not exactly as easy as falling off a log, but it isn't really that bad. Here is one way to remember the rules for IFR alternates and minimums: The first cornerstone or anchor memory aid is, literally, as simple as one-two-three. They represent three "ifs": the "one" refers to hours of time; the "two" is for ceiling in thousands of feet; and the "three" represents visibility in statute miles. Think of it like the sequence of factors for considering missed approaches: how long, how low and how far. To paraphrase this regulation, if between one hour before and one hour after the expected arrival time at your primary destination, the forecast ceiling is at least 2000 feet and the visibility is at least three statute miles--note that's an "and" not an "or"--you don't need to specify an alternate. Otherwise, dig out the charts.

The second anchor point, one which follows along nicely, is the number 45. (1-2-3, and then 4-5...get it?) This is the rule saying if you don't need an alternate, you must have enough fuel to fly another 45 minutes past your destination, at normal cruise. It's your job to calculate your likely en route time given forecast winds aloft, intended power settings and true airspeed. I'd advise throwing in another half hour for unexpected vectors and other delays. The other part of this second part, if you will, says that if the weather does dictate filing an alternate, you must have enough gas to fly to the primary destination, fly to your alternate, then on top of that fly 45 minutes more, again at normal cruise power. One more time: These are FAA minimums. If I were you, I'd fudge those up a bit in your own favor.

Of course for those new to IFR-anything, I should note here that pilots can certainly fly under instrument flight rules to a grass strip with no instrument approach whatsoever. In most cases if your destination doesn't have an instrument approach, the ceiling and visibility must be good enough for you to proceed VFR from the so-called minimum en route altitude, or MEA. In cases where you're flying in a radar environment, ATC may be able to descend you down to what's called a minimum vectoring altitude, which can be lower. Usually only the controller will know what altitude that is, for whichever sector of airspace you're flying through at that time.


The 1-2-3 rule covers the primary destination, but the regulations go a little further than this: The next one covers your alternate, as far as something known as "alternate minimums." This one can be remembered as the "602 or 802" rule. It says that as far as your alternate goes, if specific alternate minimums are not published for that airport (more on this in a minute), and if between an hour before and an hour after you expect to get there (same as the 1-2-3 rule), the airport is expected to have at least a 600-foot ceiling and two miles visibility, you can use it if and only if it has a precision approach procedure. If it has only a non-precision approach procedure, everything stays the same except the 600-foot minimum ceiling goes up to 800 feet. These are the so-called standard alternate minimums.

Some airports, because of terrain or obstructions, have different ones. Jeppesen includes them right on the approach plates for each airport whether they're standard or not (usually on the back or "airport layout" side of just the first approach plate when an airport has more than one), but you'll have to look elsewhere for this information if you're using approach plates produced by the gummint.

The one other very important thing to note here is that these alternate minimums aren't for actually landing at your alternate; they're just for your advance planning option in case you need to divert there. If you do "go missed" at your chosen primary destination and you then fly towards your alternate, you simply pull out the approach plate for your alternate airport (or much better and much wiser, you already had it out ready to go, underneath your first ones) and fly according to the published minimums for that airport, just like you did with the first one. That sometimes comes as an "Oh, really?" revelation to those first learning about IFR procedures. I know it was, for me, way back when.


So much for the FAA rules (See, that wasn't so bad, was it?), but now we come to the realm of judgment and strategy. How do you know which alternate will work out and which won't? Of course, as in-flight data trickles down to general aviation cockpits everywhere, all of it eventually will be right in front of us. But if you aren't an early adopter (or even a middle level one) and you don't have up-to-the minute METAR reports on display in the cockpit, Flight Watch certainly will be able to provide them to you. It'll just take a bit longer. Also, you can never be sure those forecasts will come true, so never assume the destination weather and winds will match those for which you have so carefully planned. But what else can you do about it?

As a general rule, when you're fishing for a good alternate, pick something big. After all, you'll need to know what the forecast is so you can plan whether to use it or not, so why not remove as much uncertainty as possible? The bigger airports have weather reporting capability, not to mention precision approaches, fantastically well-lit runways and approach light systems, as well as helpful ATC personnel right there when you may need them most.

One caveat about large airports: They can be busy, so plan for enough "extra, extra fuel" to cover delays or simply being vectored hither and yon before you get to land there. (Again, it's that fudge factor.) As far as weather surprises go, until there are National Weather Service metrics for unexpected drops in ceilings and visibility, compared to the current forecast, also given right along with each updated METAR--and don't hold your breath waiting for it--the one thing you can do to get a jump on changes is compare them yourself as you go, listening for AWOS and ATIS broadcasts along the way.

However, it doesn't require any work at all to know that the odds of needing that alternate will go way up when there are widespread low ceilings and visibilities; if several reporting points are updating their sequence reports with "specials" (or the terminal aerodrome forecasts are being amended), watch out! The other time-honored way that you can get updated information of course is, again, via Flight Watch.

Finally, and in case you were wondering, there are no FAA rules for an "alternate alternate" in case the weather really goes down the tubes and you can't get into either your destination or your alternate, even after factoring in that conservative 1-2-3 at your primary. Sort of gives new definition to "on your own," doesn't it?


Where I fly in the mid-Atlantic region, the average price of 100LL has reached over four dollars a gallon. (I don't really even ask anymore.) However, when you've gone missed and then can't get into your alternate because of worsening weather, the cost for having taken on extra fuel probably won't even register on your radar screen of unwelcome annoyances.

And, on the subject of worsening weather and having to go even further away to get back to Earth, in populated areas such as mine, that 45 minutes I mentioned earlier is probably getting close to having enough extra fuel. But if you fly west of the Mississippi, or anywhere else where airports are few and further between, you might want to make that two hours of extra fuel. That's right--I said two hours.

There are two motivations for planning IFR flights in such exhausting detail like this. Truth be told, IFR flight planning is actually easier than VFR planning in a way, because it's so procedural, and because many of the airspace permissions are already taken care of, so to speak. The first motivation is safety, of course.

The minimums and backup planning I've described exist to keep you and your passengers as far away as possible from having no options left. The second motivation is a three-letter acronym: CYA. If something ever does go amiss on a flight, you can be sure that the FAA will be looking to see how well you had planned and prepared for it.

At the end of the day, choosing and filing an alternate airport isn't rocket science; the most suitable one may be the nearest runway with an ILS. As these pages have tried to hammer home on many occasions, the need for an alternate landing facility shouldn't come as a surprise: Good airmanship requires monitoring the flight's progress, the weather and fuel. The only time any of this should be a surprise is when the guy in front of you forgets to lower his gear, closing the airport.

GPS And Alternates

Having an IFR-approved GPS navigator with a color moving map in the panel has revolutionized IFR flying in personal aircraft, especially when single-pilot. Many of us, myself included, have come to depend on GPS and rarely even tune a VOR any more except to complete the required airborne accuracy checks every now and then. Regardless of whether we've grown too dependent on GPS for en route and approach navigation, planning for and diverting to an alternate under IFR means we can't count on our magic boxes to get us there and get us down.

According to the FAA's Instrument Flying Handbook, FAA-H-8083-15:

if proceeding to an alternate airport, the avionics necessary to receive all of the ground-based facilities appropriate for the route to the alternate airport must be installed and operational. the alternate airport must be served by an approach based on other than GPS or LORAN-C navigation, the aircraft must have operational equipment capable of using that navigation aid, and the required navigation aid must be operational.

In other words, you can't legally choose an alternate airport served only by a GPS-based approach procedure (does anybody use Loran-C any more?) or depend only on GPS to get you there.

To the extent one can apply such a concept to the FAA, this is "consistent" with the agency's policy regarding GPS substitution for DME and ADF receivers. Also from the Instrument Flying Handbook:

A non-GPS approach procedure must exist at the alternate airport when one is required. if the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate.

In theory, most of this makes sense, the exception being related to ADF--GPS accuracy and ease of use is light-years ahead (we wouldn't hesitate to use GPS to identify a LOM or shoot an NDB procedure in our database in lieu of the ADF we yanked out almost a decade ago). But our bottom line is this: We wouldn't file an alternate that didn't have an ILS to begin with. If the weather's that bad, we want the best we can get. -- J.B.


The Right Answer

For me, the whole idea behind getting the Instrument ticket was that I wouldn't again be grounded so darned often. But increasing your private transportation's utility, at least for the foreseeable future, has its limits. For example, what happens when there are low ceilings and visibility over a wide area? The answer in this case is, of necessity, humorless and unequivocal: If you discover your first choice for a destination is out of the running, you'd better know where the nearest acceptable weather is and have more than enough fuel to fly there.

During the oral exam for my Instrument rating, the examiner posed just such a hypothetical situation to me. She asked what I would do if the ceilings and visibilities were below minimums for several hundred miles. To me, the answer seemed obvious, but also too easy; I suspected it was a trick. However, I couldn't figure out just what lesson I was supposed to be inferring from this probing question, so after what seemed like an interminable five seconds or so, I blurted out what I'd thought right off: I just wouldn't frikkin' take off (only I didn't put it that way).


As it turned out, that was the answer she thought was best.

Jeff Pardo is a freelance writer and editor who holds a Commercial certificate for airplanes, helicopters and sailplanes.

The Zero-Zero Alternate

So far, we've been talking about landing--or destination--alternates, those we'll need at the end of a trip. For most Part 91 operators, that's the only legal requirement the FAA imposes. But what about takeoff alternates? The FAA imposes on Part 135 and 121 operators requirements for a takeoff alternate to be designated under certain circumstances. For Part 91, it might not be a bad idea.

Part 121 operators are required to have a takeoff alternate airport for their departure airport in addition to their airport of intended landing if the weather at the departure airport is below the landing minimums. For two-engine aircraft, the alternate must be within one hour flying time on one engine. The airport of intended landing may be used in lieu of an alternate providing it meets all the requirements. Part 135 operators are also subject to similar, though different, rules.

For Part 91 guys--especially when driving a single--some of this is overkill. Still, when departing into low IFR, there are any number of reasons short of engine failure that may require diverting to a nearby airport shortly after takeoff.

And, since Part 91 allows us to take off into zero-zero conditions, we need to be extra careful in our planning--and preflight checks--to ensure everything's secure and working when we launch. Finally, it doesn't hurt a thing to set up the radios and cockpit for the likeliest approach before taking the active. --J.B.


If a cabin, baggage or access door wasn't secured and can't be closed in-flight, what will you do if everything close by is below minimums?


Despite all the pre-flight checks, sometimes we won't know something isn't working--radios, for example--until airborne.


In addition to failing to extend, flaps and landing gear also can fail to retract after takeoff. Sure, you have the fuel to reach decent weather with everything working, but what about when dragging the gear?
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Author:Pardo, Jeff
Publication:Aviation Safety
Geographic Code:1USA
Date:Aug 1, 2007
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