IFR - personal minimums question

Matthew

Matthew

Touchdown! Greaser!
Joined
Apr 18, 2005
Messages
18,650
Location
kojc, kixd, k34
Display Name
Display name:
Matthew
I’m still working on that rating. The bad part about winter is canceling a lot of lessons, but the good thing is getting to experience a whole lot of different conditions.

One thing I’m working on is learning to set new personal minimums for IFR vs VFR.

Here’s a real world example from today: clg are 600’, surface temps are 5C (40F), elevation is right about 1000’. The charts show a freezing level of 4000’ and my training flight would be about 3500’. The 4000’ line is right on top of us, and right on the other side is sfc-4000’ freezing levels. The potential for <0C + IMC was pretty high so we canceled.

I’m still learning: what’s a good safety margin? What to look and look out for? I’ve had this discussion with my CFII but am wondering how others look at it.
 
I’m not sure what you mean by feeezing levels Sfc-4000 “right on the other side”, but aside from that it sounds to me like a decent training day. You’re planning to be below the freezing level, but you’ve got some outs if you’re not.
 
MauleSkinner said:
I’m not sure what you mean by feeezing levels Sfc-4000 “right on the other side”, but aside from that it sounds to me like a decent training day. You’re planning to be below the freezing level, but you’ve got some outs if you’re not.
Click to expand...
There’s an area showing freezing level sfc-8000 (I know I typed 4000) right next to the 4000’ line that’s right over top of me. So even if you trust that 4000 level, you don’t have to get very far before freezing levels could get a lot lower.

I’m trying to judge what’s a good margin to allow. For example: If you’re planning flight at an altitude 500’ below a predicted freezing level, is that an OK decision to go or is that cutting it too close (and why?)
 
TommyG said:
Anything close to ice, I don’t mess around. For me that margin is too close.
Click to expand...
I’m in agreement there. I’m trying to figure how close is too close? This is more complicated that a simple “500’ below” cloud clearance.
 
What bit me was freezing rain. I thought I was safely below, and was, until it decided to rain (unforecasted)

Being from Florida, and after that situation, I'll stay in the south in the winter.
 
M2C- don’t fly where you are less than 40 degrees F. Or just stay at least 2000 feet below freezing level.

Your 500 foot buffer would put you within around 2 degrees of freezing. Far too close, as weather changes quickly, the forecasts aren’t that precise, and the consequences are severe
 
Last edited:
I would've gone by this. No icing forecast in the KC area right now at 5k. But I would also say, have an out. Forecasts have a way of being wrong.

upload_2023-3-23_15-3-36.png
 
NealRomeoGolf said:
I would've gone by this. No icing forecast in the KC area right now at 5k. But I would also say, have an out. Forecasts have a way of being wrong.

View attachment 116012
Click to expand...
Thx. No icing airmets now. I got a briefing early this morning for mid-day, and things were looking more dire then. I think 1-800-wx-brief keeps a PDF history of briefings. Maybe I'll see if I can find the one from this morning. I honestly can't remember if I saw an icing airment then or if I was just looking at the clg and freezing levels.
 
WDD said:
M2C- don’t fly where you are less than 40 degrees F. Or just stay at least 2000 feet below freezing level.

Your 500 foot buffer would put you within around 2 degrees of freezing. Far too close, as weather changes quickly, the forecasts aren’t that precise, and the consequences are severe
Click to expand...
Yeah, I'm hearing "don't trust the forecast for freezing levels". I looked at surface temps, then did the lapse rate numbers and came up with a number that was pretty close to predicted.
 
Matthew said:
Thx. No icing airmets now. I got a briefing early this morning for mid-day, and things were looking more dire then. I think 1-800-wx-brief keeps a PDF history of briefings. Maybe I'll see if I can find the one from this morning. I honestly can't remember if I saw an icing airment then or if I was just looking at the clg and freezing levels.
Click to expand...
Would be curious to see the briefing. The skews right now say the freezing level is much higher. Based on the skews I'd be flying. It has a small bit at 3k where it dips to 31. Above it, it gets as warm as 46. So you have an out both up and down.
 
NealRomeoGolf said:
Would be curious to see the briefing. The skews right now say the freezing level is much higher. Based on the skews I'd be flying. It has a small bit at 3k where it dips to 31. Above it, it gets as warm as 46. So you have an out both up and down.
Click to expand...
I haven't used skew-T charts for a long time. I keep forgetting they are a useful thing. I'll see if I can find that briefing, if it doesn't take too long. I missed my schedule window for the rest of the day anyway.
 
Matthew said:
I haven't used skew-T charts for a long time. I keep forgetting they are a useful thing. I'll see if I can find that briefing, if it doesn't take too long. I missed my schedule window for the rest of the day anyway.
Click to expand...
I have been trying to learn this ice stuff too. I'm not quite at 2 years on my IFR yet and it is still hard for me to decide. It's easy for me to arm chair for you though. :) I need to fly up to Milwaukee tomorrow morning so been watching the freezing levels myself.
 
Part of the calculus around freezing level is the lowest level ATC would give you on a clearance. Around here (Chicagoland) that's typically 3000. Lowest freezing level is one view into the weather, but remember that you can get ice at temps warmer than 0 C. In this scenario related to ice, I'd look at a skew-T or the winds aloft chart to see temps. But at 40F, unless there's a decent inversion, I'm probably staying on the ground.

I have flown in actual and on an approach to OVC006 at 7C (45F) and felt OK, but there was an inversion to 6000ft, and zero noted on FIP/CIP.
 
kaiser said:
Part of the calculus around freezing level is the lowest level ATC would give you on a clearance. Around here (Chicagoland) that's typically 3000. Lowest freezing level is one view into the weather, but remember that you can get ice at temps warmer than 0 C. In this scenario related to ice, I'd look at a skew-T or the winds aloft chart to see temps. But at 40F, unless there's a decent inversion, I'm probably staying on the ground.

I have flown in actual and on an approach to OVC006 at 7C (45F) and felt OK, but there was an inversion to 6000ft, and zero noted on FIP/CIP.
Click to expand...
thanks.

Until now, this winter was pretty simple to figure out: it's howling wind, or freezing rain, or <=20F and my FBO won't dispatch a plane when it's that cold, or it's >20F and crystal clear. Now I'm in the changeover period where it isn't really winter and it isn't really spring, and I'm starting to deal with a lot more variables. I'm trying to figure out a simple way to go/no-go but I'm learning that it really isn't that simple.
 
NealRomeoGolf said:
Would be curious to see the briefing. The skews right now say the freezing level is much higher. Based on the skews I'd be flying. It has a small bit at 3k where it dips to 31. Above it, it gets as warm as 46. So you have an out both up and down.
Click to expand...
I found the briefing - there were no icing airmets, only for freezing levels and IFR. At the time of the brief, things were 6SM BR OVC006. The TAF for the flight time was 6SM BR OVC007 and conditions at the scheduled flight time pretty much matched the TAF.
 
Another source of information is the forecast temperature on the FD.
 
Here's one for you.

  • Current location is clear skies, and clear skies enroute.
  • Destination is coastal, recently became 100% overcast.
  • Not likely to improve.
  • It's 11AM and the flight is 2hrs.
  • Temperature at the airport surface (500'msl) is 49 deg F.
  • Tops at destination are 7,000 with ceilings 4,500.
  • Field elevation is 500'.
  • Approaches are available, precision and non, with various sub-1000' MAPs.
  • There are no PIREPs of ice.
 
Ice in the forecast is a non starter for me. ADDS is a great resource for ice prediction too.
 
Rucsoundings.noaa.gov

Extremely useful for situations like these. VERY common to have an inversion in the winter. I flew some approaches for currency yesterday. It was 5C on the ground and 8C at 4000. Will also show you how thick the layer will likely be. I also like the icing layer on the map at 1800wxbrief. I like the 25% chance and SLD options. Pireps overrule everything.

You'll find that airmets are completely useless, and freezing layer charts are only the starting point to see if you need to be checking other sources.
 
I canx'd a XC to Chicago last week ago over icing and MVFR cloud cover. Essentially it would have meant scud running from just north of Little Rock all the way to Midway, to stay below the clouds circa OVC020 up past Champaign, and getting worse the later in the evening. Freezing temps pretty much at the cloud base, going towards the surface by destination. Doable, with little slop in the schedule before it turned into IFR in icing. IOW, stoopid. So www dot united dot com time it was. Bohica $$$, but we're alive.

In the end, my minimums recreationally boil down to my lack of faith in my lawnmower's performance, not my ability to read or interpret icing forecasting data. I also do not consider "warm above" a mitigation COA of consequence when deciding go-no go, given said equipment. I assume my airplane will not be able to climb through a forecast icing layer to the degree necessary to maintain safety of flight. To say nothing of the legalities of accreting structural ice through a layer the FAA had forecasting data positive for icing at said altitude and location. Now I gotta get myself back down through the same layer of now known-to-me icing, and playing the priority game with ATC hoping they get me down in time before I turn into a popsicle. Or worse, declaring the E-word and now it's on tape I effed around and found out wrt icing rules while non-FIKI. No thanks, this is supposed to be fun and I got an ATP to protect for a little while longer.

My matrix is pretty easy, though conservative. With FIKI and about 100-200HP additional horsepower, I'd be willing to punch through mod icing layers of 5k or less (they often are, skew-T makes that an easy assessment) with the information available in ADDS and other FAA sanctioned sources, without concern. But that's not the equipment I can afford, so it's moot.

The amount of info available these days on ADDS is truly amazing. It's really not all that complicated to paint a picture of freezing levels and moisture fronts, and put two and two together and come up with a vertical picture. The icing forecast tool is also very illustrative for those of us who do the 800NM+ a day thing.
 
Training flight, lowish IMC, freezing level forecast close to MEA or MVA?
No thanks.

Look at pireps for a good idea of actual conditions. Always have a solid out before going into the soup. The out I like is temps above freezing below my position with at least a 4000 ft cushion over MEA. It doesn't feel good when you are at MEA with ice and no options as you're going over terrain.
 
Rgbeard said:
Here's one for you.

  • Current location is clear skies, and clear skies enroute.
  • Destination is coastal, recently became 100% overcast.
  • Not likely to improve.
  • It's 11AM and the flight is 2hrs.
  • Temperature at the airport surface (500'msl) is 49 deg F.
  • Tops at destination are 7,000 with ceilings 4,500.
  • Field elevation is 500'.
  • Approaches are available, precision and non, with various sub-1000' MAPs.
  • There are no PIREPs of ice.
Click to expand...
I’m going to have to ponder this one later tonight.
 
FORANE said:
Training flight, lowish IMC, freezing level forecast close to MEA or MVA?
No thanks.

Look at pireps for a good idea of actual conditions. Always have a solid out before going into the soup. The out I like is temps above freezing below my position with at least a 4000 ft cushion over MEA. It doesn't feel good when you are at MEA with ice and no options as you're going over terrain.
Click to expand...
That’s a good answer. It includes a “why”.
 
hindsight2020 said:
I canx'd a XC to Chicago last week ago over icing and MVFR cloud cover. Essentially it would have meant scud running from just north of Little Rock all the way to Midway, to stay below the clouds circa OVC020 up past Champaign, and getting worse the later in the evening. Freezing temps pretty much at the cloud base, going towards the surface by destination. Doable, with little slop in the schedule before it turned into IFR in icing. IOW, stoopid. So www dot united dot com time it was. Bohica $$$, but we're alive.

In the end, my minimums recreationally boil down to my lack of faith in my lawnmower's performance, not my ability to read or interpret icing forecasting data. I also do not consider "warm above" a mitigation COA of consequence when deciding go-no go, given said equipment. I assume my airplane will not be able to climb through a forecast icing layer to the degree necessary to maintain safety of flight. To say nothing of the legalities of accreting structural ice through a layer the FAA had forecasting data positive for icing at said altitude and location. Now I gotta get myself back down through the same layer of now known-to-me icing, and playing the priority game with ATC hoping they get me down in time before I turn into a popsicle. Or worse, declaring the E-word and now it's on tape I effed around and found out wrt icing rules while non-FIKI. No thanks, this is supposed to be fun and I got an ATP to protect for a little while longer.

My matrix is pretty easy, though conservative. With FIKI and about 100-200HP additional horsepower, I'd be willing to punch through mod icing layers of 5k or less (they often are, skew-T makes that an easy assessment) with the information available in ADDS and other FAA sanctioned sources, without concern. But that's not the equipment I can afford, so it's moot.

The amount of info available these days on ADDS is truly amazing. It's really not all that complicated to paint a picture of freezing levels and moisture fronts, and put two and two together and come up with a vertical picture. The icing forecast tool is also very illustrative for those of us who do the 800NM+ a day thing.
Click to expand...
FWIW

I chose to make an IFR flight across central IL that same day. I did encounter IMC below 0c, but did not pick up any ice. I had the advantage of a much shorter flight, in my backyard, and I was not going any farther north than Champaign. I probably would've scrubbed had I been going north. We also left the party a bit early as the rain was moving in from the west and while I'm willing to push a little bit on the icing side, not SLD, and not at night.

Point being I don't think there's a hard "minimum", but more of a confluence of factors that even reasonable pilots can disagree on.
 
Rgbeard said:
Here's one for you.

  • Current location is clear skies, and clear skies enroute.
  • Destination is coastal, recently became 100% overcast.
  • Not likely to improve.
  • It's 11AM and the flight is 2hrs.
  • Temperature at the airport surface (500'msl) is 49 deg F.
  • Tops at destination are 7,000 with ceilings 4,500.
  • Field elevation is 500'.
  • Approaches are available, precision and non, with various sub-1000' MAPs.
  • There are no PIREPs of ice.
Click to expand...
Excellent VFR! Why are you including that in an IFR discussion? ;)
 
Jim K said:
FWIW

Point being I don't think there's a hard "minimum", but more of a confluence of factors that even reasonable pilots can disagree on.
Click to expand...

Of course. And I wasn't trying to be normative about my opinion either, but the thermodynamics of icing are not a matter of interpretation. To be clear, what you seem to be debating is the merits of forecasting.
 
Last edited:
My favorite part is when you study the forecasts for a long while the night before and worry about it all night and then you wake up to clear skies. These forecasters, I tell ya. So much for BKN025.
 
NealRomeoGolf said:
My favorite part is when you study the forecasts for a long while the night before and worry about it all night and then you wake up to clear skies. These forecasters, I tell ya. So much for BKN025.
Click to expand...
I started reading the forecast discussion. Sometimes there are interesting reasons behind why they guess what they do.
 
Rgbeard said:
Here's one for you.

  • Current location is clear skies, and clear skies enroute.
  • Destination is coastal, recently became 100% overcast.
  • Not likely to improve.
  • It's 11AM and the flight is 2hrs.
  • Temperature at the airport surface (500'msl) is 49 deg F.
  • Tops at destination are 7,000 with ceilings 4,500.
  • Field elevation is 500'.
  • Approaches are available, precision and non, with various sub-1000' MAPs.
  • There are no PIREPs of ice.
Click to expand...
Had a chance to get back to this. Clg at destination is 4500, clear everywhere else and a 2 hr window? I don’t know anything about coastal conditions, so I don’t know if that info is relevant. And I didn’t see anything here about terrain. But around here, unless the forecast is for something really bad, or the winds are too strong, that’s good vfr.

I see the “not likely to improve” but I didn’t see the “not likely to get worse” comment though. And the tops at 7000 make for a pretty thick layer, like something big is moving in. What’s the forecast say?
 
Matthew said:
I started reading the forecast discussion. Sometimes there are interesting reasons behind why they guess what they do.
Click to expand...
I do that too but sometimes you get those forecasters that just want to talk technical and you have no idea what they're saying. Others are good about what they are describing.

It was an easy flight this morning. Now I have to watch for the ice going back later. Should be warm enough though.
 
Last edited:
Rgbeard said:
Here's one for you.

  • Current location is clear skies, and clear skies enroute.
  • Destination is coastal, recently became 100% overcast.
  • Not likely to improve.
  • It's 11AM and the flight is 2hrs.
  • Temperature at the airport surface (500'msl) is 49 deg F.
  • Tops at destination are 7,000 with ceilings 4,500.
  • Field elevation is 500'.
  • Approaches are available, precision and non, with various sub-1000' MAPs.
  • There are no PIREPs of ice.
Click to expand...

Not enough info. Which airport (departure or destination) is at 49F?

What’s the freezing level and what’s the cruise altitude?
 
Matthew said:
Had a chance to get back to this. Clg at destination is 4500, clear everywhere else and a 2 hr window? I don’t know anything about coastal conditions, so I don’t know if that info is relevant. And I didn’t see anything here about terrain. But around here, unless the forecast is for something really bad, or the winds are too strong, that’s good vfr.

I see the “not likely to improve” but I didn’t see the “not likely to get worse” comment though. And the tops at 7000 make for a pretty thick layer, like something big is moving in. What’s the forecast say?
Click to expand...


What I am painting is San Diego, commonly in the Winter. Terrain prevents you from arriving below the ceiling. I didn’t make that clear. Sorry. Question still stands. I have been forced into this scenario more than once
 
TCABM said:
Not enough info. Which airport (departure or destination) is at 49F?

What’s the freezing level and what’s the cruise altitude?
Click to expand...

1. destination
2. You can calculate the FL, 6,000 seems reasonable.
3. Cruise 8500 or higher due to destinations terrain that ends at the ovc area and opens to a largea area of near-sea-level terrain.
I.E. San Diego Brown Field arriving from the East.
 
Rgbeard said:
What I am painting is San Diego, commonly in the Winter. Terrain prevents you from arriving below the ceiling. I didn’t make that clear. Sorry. Question still stands. I have been forced into this scenario more than once
Click to expand...
That’s a good scenario, though, makes you think about more than just a clg metar and taf.

There are some places south of here that have similar terrain issues and can really cause problems on departures. Looks simple on paper, then you have consider terrain, and that kind of thing doesn’t show on a weather forecast.
 
Matthew said:
That’s a good scenario, though, makes you think about more than just a clg metar and taf.

There are some places south of here that have similar terrain issues and can really cause problems on departures. Looks simple on paper, then you have consider terrain, and that kind of thing doesn’t show on a weather forecast.
Click to expand...

@Matthew

so it’s not set to improve for at least 12hr and your favorite lunch is on the other side. You flying this one?
 
Rgbeard said:
@Matthew

so it’s not set to improve for at least 12hr and your favorite lunch is on the other side. You flying this one?
Click to expand...
Looking back a bit at your scenario: tops at 7000, surface temps (500') are 9C. Assuming -2C per thousand, tops might be at -4C.

I'n my experience level, that's visible moisture + freezing temps.
 
One of the things I had to get used to when I started flying, was the idea of operating in 3 dimensions, not just 2D like a car. IR training is really bringing that together in ways other than just operating the aircraft.

Good stuff.
 
You must log in or register to reply here.
Back
Top