What’s the logic of IFR alternate minimums?

[RobertE]

Beyond the fact that establishing in one’s mind the reality that an airport might have different weather than forecast so you better be ready with a backup, I don’t really understand the basis of the logic for the minimums at the alternate.  As we all know, the 123 rule means an alternate is necessary if the primary airport is worse than 2000 and 3 miles.  But aren’t any conditions that change enough to produce a miss at that airport far more likely to deteriorate at the alternate airport that needs only, typically, 600 or 800 and 2 miles (or at some airports 200 and 1 mile)?  It doesn’t seem like a prudent, true backup.  

Anyone know how these rules came to be?  Is it just a practical expedient the FAA gave us because the distance to a new weather system would, typically, be just too darn far for much IFR flight otherwise?

Just curious.

[steingar]

My thinking is I would set up alternates such that if I'm making a GPS approach to my intended destination then my alternate is going to have an ILS.  If you've a WAAS capable GPS and multiple LNAV approaches then I agree its more a paperwork exercise than anything.  But for those of us in the cheap seats it can be a good risk management tool.

[gsengle]

It basically says if the weather at your destination is anything other than “gentleman’s IFR” you need an alternate. This makes you carry enough fuel in addition to the 45 mins to get to your alternate, so it basically just ups your fuel reserves in the case the weather is the least bit low.

 

Then you have to ask pick a suitable alternate so that your extra fuel reserves are somewhat related to how far you likely need to go. The forecast at your alternate has to be pretty good, so it might have to be far away, way increasing your fuel load.

 

It’s all about fuel planning. When you actually divert you go to wherever makes the most sense at the time.

 

And to answer your other question, no, the weather phenomena that make it that low tend to be somewhat localized like heavy rain, coastal fog, valley fog, etc.

 

(My day job is a Captain at Cape Air - we know low IFR)

 

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[Bob - S50]

I'm guessing statistics.  The odds of weather going down at both places is much less likely than it is of going down at one place.  But of course, pilots can out smart the odds by picking an alternate that is only a few miles from the destination.  That way they can both go down.

[Marauder]

It basically says if the weather at your destination is anything other than “gentleman’s IFR” you need an alternate. This makes you carry enough fuel in addition to the 45 mins to get to your alternate, so it basically just ups your fuel reserves in the case the weather is the least bit low.
 
Then you have to ask pick a suitable alternate so that your extra fuel reserves are somewhat related to how far you likely need to go. The forecast at your alternate has to be pretty good, so it might have to be far away, way increasing your fuel load.
 
It’s all about fuel planning. When you actually divert you go to wherever makes the most sense at the time.
 
And to answer your other question, no, the weather phenomena that make it that low tend to be somewhat localized like heavy rain, coastal fog, valley fog, etc.
 
(My day job is a Captain at Cape Air - we know low IFR)
 
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There was an accident here in Delaware that epitomizes your reply. A doctor flying in an Arrow from North Carolina into Delaware was met with widespread low IFR. He missed at multiple airports and then ended up crashing within a few miles of Dover AFB after running out of fuel.

Based on the conditions, it would have been prudent to have made a fuel stop at a minimum or based on actual conditions that he would be encountering to have cancelled the flight.


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[gsengle]

There was an accident here in Delaware that epitomizes your reply. A doctor flying in an Arrow from North Carolina into Delaware was met with widespread low IFR. He missed at multiple airports and then ended up crashing within a few miles of Dover AFB after running out of fuel.

Based on the conditions, it would have been prudent to have made a fuel stop at a minimum or based on actual conditions that he would be encountering to have cancelled the flight.


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Personally widespread low IFR is a no go in a single. No options in case of engine failure. It’s the one scenario that makes me dream about a twin as much as I love the Mooney.

Usually widespread low IFR is certainly forecast well enough to make you have to look far away for alternates that meet the rules too... I’ve used Albany once as an alternate on a flight from HYA to ACK. Was only thing that fit the rules and made me carry 300lbs extra fuel on top of the 45 mins...


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[AH-1 Cobra Pilot]

Logic?  In FAA regulations?  Surely, you jest?

[gsengle]

Logic?  In FAA regulations?  Surely, you jest?

Often I’d agree, but when you fly a lot of IFR you actually see in practice that these particular rules are pretty good... imho


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[AH-1 Cobra Pilot]

After flying several military branches, privately, and commercially, there are numerous different rules.  Some minimums exceed the FARs, and some are less stringent.  I have found no particular reasons for the differences, other than, "That is the way we have always done it."

[RobertGary1]

Maybe just practical. If there is a large area of ceilings below 2,000 it would ground aircraft. 

-Robert 

[gsengle]

After flying several military branches, privately, and commercially, there are numerous different rules.  Some minimums exceed the FARs, and some are less stringent.  I have found no particular reasons for the differences, other than, "That is the way we have always done it."

Yup that Id agree with. Our 135 opspecs are different from the part 91 standard rules in minor ways which I haven’t figured out the purpose for yet. But generally I suspect tweaks to the rule fall into 2 categories.

1) areas where your company has training and or equipment in place to make specific ops safe, like 1800rvr when flying a coupled approach.

2) areas where a particular airport is regularly problematic so you ask for a tweak that makes that airport work.


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[steingar]

1 hour ago, Marauder said:

There was an accident here in Delaware that epitomizes your reply. A doctor flying in an Arrow from North Carolina into Delaware was met with widespread low IFR. He missed at multiple airports and then ended up crashing within a few miles of Dover AFB after running out of fuel.

Based on the conditions, it would have been prudent to have made a fuel stop at a minimum or based on actual conditions that he would be encountering to have cancelled the flight.

 

If this is the same crash I'm thinking of (there is an accident analysis of it on Youtube) it didn't help that he didn't go down to minimums on the approach, but stopped his descents somewhat higher.  For what I recall he would have made it had he gone down to the minimum descent altitude on a couple of his approaches.  

But I have to agree with gsengle, when things go down around here they can do so over a very wide area.  

[Seth]

1 minute ago, steingar said:

If this is the same crash I'm thinking of (there is an accident analysis of it on Youtube) it didn't help that he didn't go down to minimums on the approach, but stopped his descents somewhat higher.  For what I recall he would have made it had he gone down to the minimum descent altitude on a couple of his approaches.  

But I have to agree with gsengle, when things go down around here they can do so over a very wide area.  

Yes that’s the one

[ilovecornfields]

9 minutes ago, Seth said:

Yes that’s the one

I watched that a while ago and it sounds like he messed up several approaches on the way, not entirely clear why. That last transmission where he was engine out in IMC was disturbing. I felt like I could tell from the tone that he knew it was over.

[jaylw314]

10 minutes ago, ilovecornfields said:

I watched that a while ago and it sounds like he messed up several approaches on the way, not entirely clear why. That last transmission where he was engine out in IMC was disturbing. I felt like I could tell from the tone that he knew it was over.

IIRC, at some point he reported some unspecified "problem with GPS."  Of course, it's unclear if it was a hardware or pilot problem.

Luckily here on the west coast, widespread IFR is unlikely, so good alternates make sense.  Here in the Willamette Valley in Oregon, I usually use Bend, OR as an alternate even when flying IFR locally, because it is on the leeward side of the Cascades.  With all the mountains on the West Coast, SOMEONE is bound to have better weather than where I am

[Marauder]

If this is the same crash I'm thinking of (there is an accident analysis of it on Youtube) it didn't help that he didn't go down to minimums on the approach, but stopped his descents somewhat higher.  For what I recall he would have made it had he gone down to the minimum descent altitude on a couple of his approaches.  
But I have to agree with gsengle, when things go down around here they can do so over a very wide area.  

One of the dependencies in IFR flying is the level of currency the pilot can maintain. I know from my own personal experience, if I am doing a bunch of visual approaches recently and haven’t flown to mins in actual conditions in a while, you’re not going to catch me in the conditions that this pilot flew. Just because you are technically current doesn’t mean you’re competent to fly it.

I recall the accident pilot claiming he was having difficulty with his GPS and also not flying the ILS even though the plane was equipped to do so. Based on the ILS approach being available, there was a good chance he would have made it in. So, why didn’t he fly it? Flying with faulty equipment? Child of the magenta line?


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[jaylw314]

1 hour ago, Marauder said:

One of the dependencies in IFR flying is the level of currency the pilot can maintain. I know from my own personal experience, if I am doing a bunch of visual approaches recently and haven’t flown to mins in actual conditions in a while, you’re not going to catch me in the conditions that this pilot flew. Just because you are technically current doesn’t mean you’re competent to fly it.

I recall the accident pilot claiming he was having difficulty with his GPS and also not flying the ILS even though the plane was equipped to do so. Based on the ILS approach being available, there was a good chance he would have made it in. So, why didn’t he fly it? Flying with faulty equipment? Child of the magenta line?


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Complete speculation on my part, but hearing the transcript, I'm guessing he had a G430 or 530 and had programmed the ILS approach, but neglected to change the ILS frequency to active.  He was trying to figure out why the localizer needle was not moving, and was trying to continue the approach by the magenta line, hence wandering all over the general approach course.  At some point, he figured it out, but the tower controller was the one who suggested the LOC approach only and he accepted.  Sometime in the middle of all that was when he realized his vacuum pump failed, but his mistake with the ILS frequency may have delayed recognizing a more serious problem was occurring.

[Seth]

At the 135 I'm training at, there are even more rules.  Non-accurate example:  If the alternate only has 1 approach, the expected forecast must be clouds 600 AGL or better.  If two approaches (must be to two different runways), it can be 400 AGL (lower).  They regiment the process to make the decision for you to ensure you have an out vs legally allowing yourself to be in a really bad place.

So when coming back to GAI, the home base for most of the aircraft, the alternate will likely be BWI or IAD.

I'm learning a ton at the local part 135 charter company - and it's flying Cirrus SR-22's, not heavy metal.  The price point difference of chartering a flight through the company I'm training at vs a King Air or light jet is massive.  That's the point for a savvy business operator.   It's a neat model and I'm happy to talk about it sometime.  All the aircraft are leasebacks maintained by the charter company to 135 standards.

 

-Seth

Edited August 23, 2018 by Seth

[jlunseth]

gsengle got it right, its a fuel rule, it makes you carry more fuel reserves.  You are not required to use your declared alternate to land, you are just required to carry the fuel to get there.  I can’t think of a time where I actually used the declared alternate, usually you find the best available airport if its really necessary. Actually, nowadays with weather on the panel, on the rare occasions when I have run into a primary airport that is going too low to land, with NEXRAD on the panel and good weather reporting  through SatWX and ADSB, I just land somewhere short of the primary and avoid the whole issue.

Edited August 24, 2018 by jlunseth

[toto]

2 hours ago, jlunseth said:

gsengle got it right, its a fuel rule, it makes you carry more fuel reserves.  You are not required to use your declared alternate to land, you are just required to carry the fuel to get there.  I can’t think of a time where I actually used the declared alternate, usually you find the best available airport if its really necessary. Actually, nowadays with weather on the panel, on the rare occasions when I have run into a primary airport that is going too low to land, with NEXRAD on the panel and good weather reporting  through SatWX and ADSB, I just land somewhere short of the primary and avoid the whole issue.

 

Are you saying that requiring higher alternate minimums is intended to force pilots to be more conservative with fuel planning?

FWIW, I always associate the filed alternate with nordo situations. 

[N201MKTurbo]

On 8/23/2018 at 5:25 AM, Marauder said:

 

There was an accident here in Delaware that epitomizes your reply. A doctor flying in an Arrow from North Carolina into Delaware was met with widespread low IFR. He missed at multiple airports and then ended up crashing within a few miles of Dover AFB after running out of fuel.

 

I’ve never been in this situation, but if I was I would pick something like the Air Force base with wide runways and crash, fire and rescue and fly an ILS down to the ground. 

Much better to crash in the landing configuration with somebody standing by to help you then in a random location. Besides there is a good chance you could pull it off unscathed.

[gsengle]

 
Are you saying that requiring higher alternate minimums is intended to force pilots to be more conservative with fuel planning?
FWIW, I always associate the filed alternate with nordo situations. 

Yep alternate minimums are 95% to do with fuel planning / reserves...


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[gsengle]

I’ve never been in this situation, but if I was I would pick something like the Air Force base with wide runways and crash, fire and rescue and fly an ILS down to the ground. 
Much better to crash in the landing configuration with somebody standing by to help you then in a random location. Besides there is a good chance you could pull it off unscathed.

Yep fly an ILS coupled right to the runway in an emergency, even at RVR 1000 you’ll pick up lights on a bright runway by 100 feet and be able to flare. Just better have those needles centered. Fly it coupled. Go to a big runway. Imho use LPV. And ask for lights on maximum.


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[exM20K]

25 minutes ago, gsengle said:

 

Yep fly an ILS coupled right to the runway in an emergency, even at RVR 1000 you’ll pick up lights on a bright runway by 100 feet and be able to flare. Just better have those needles centered. Fly it coupled. Go to a big runway. Imho use LPV. And ask for lights on maximum.


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Nantucket is awesome for LIFR!  I flew in there a bunch before and after the TDZ lights were installed (late 90's?), and the heat generated by them was often enough to lift the fog a bit.  Number of missed approaches went way down post-TDZ lighting.  Of course, a switch to LED's will ruin this effect.

-dan

Edited August 24, 2018 by exM20K

[whiskytango]

On 8/23/2018 at 10:22 AM, steingar said:

My thinking is I would set up alternates such that if I'm making a GPS approach to my intended destination then my alternate is going to have an ILS.  If you've a WAAS capable GPS and multiple LNAV approaches then I agree its more a paperwork exercise than anything.  But for those of us in the cheap seats it can be a good risk management tool.

I was taught the same thing - an ILS is the gold standard for an alternate.  Also, if you go missed on a non-precision approach, don't try it again - proceed to your alternate, with its precision approach.